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SUPRAMOLECULAR ASSEMBLY OF HALIDE PEROVSKITE

20250059439 ยท 2025-02-20

    Inventors

    Cpc classification

    International classification

    Abstract

    Halide perovskite compounds comprising at least one metal cation, at least one halide anion, and at least one alkali metal-bound crown ether, such as (crown ether@A).sub.2M(IV)X.sub.6, (crown ether@A)M(II)X.sub.4, or (crown ether@A)M(III)X.sub.5 (A=alkali metal cation, M=metal cation, X=halide anion), such as (18C6@K).sub.2HfBr.sub.6, (18C6@K).sub.2ZrCl.sub.4Br.sub.2, (18C6@Ba)MnBr.sub.4, and (18C6@Ba)SbCl.sub.5 are provided. Methods of generating such halide perovskite compounds are also provided. The halide perovskite compounds provided herein can have improved photoluminescence quantum yield (PLQY), improved tunability, improved purity, and/or improved stability relative to available halide perovskite compounds such as alkali metal cation vacancy-ordered perovskites.

    Claims

    1. A halide perovskite compound according to the formula: (crown ether@A).sub.2M(IV)X.sub.6, wherein the M(IV) is at least one tetravalent metal cation, the X is at least one halide anion, and the crown ether@A is at least one alkali metal-bound crown ether formed between an alkali metal cation A and oxygen atoms of a crown ether.

    2. The halide perovskite compound of claim 1, wherein the M(IV) is one or more of; Te.sup.4+, Sn.sup.4+, Pt.sup.2+, Se.sup.3+, Ir.sup.4+, Zr.sup.4+, Hf.sup.4+, and Ce.sup.4+; the X is one or more of Cl.sup., Br.sup., and I.sup.; the crown ether is one or more of 18-Crown-6 (18C6) and 21-Crown-7 (21C7); and the A is one or more of Cs.sup.+, Rb.sup.+, and K.sup.+.

    3. The halide perovskite compound of claim 1, wherein the halide perovskite compound is (18-Crown-6@K).sub.2HfBr.sub.6 or (18C6@K).sub.2ZrCl.sub.4Br.sub.2.

    4. The halide perovskite compound of claim 1, comprising at least one of (i) a dumbbell-shaped structural unit formed by two [crown ether@A].sup.+s and one [M(IV)X.sub.6].sup.2, and (ii) a rhombohedral crystal structure comprising a plurality of the dumbbell-shaped structural units, wherein the [crown ether@A].sup.+ is a free charged form of the crown ether@A, and the [M(IV)X.sub.6].sup.2 is a free charged form of the M(IV)X.sub.6.

    5. The halide perovskite compound of claim 1, comprising greater photoluminescence quantum yield (PLQY) as compared to a control compound A.sub.2M(IV)X.sub.6 without the crown ether and comprising the same A, M(IV), and X as the halide perovskite compound.

    6. The halide perovskite compound of claim 5, wherein the PLQY of the halide perovskite compound is greater than 90% under excitation at 275 nm, measured at 445 nm, or greater than 80% under excitation at 295 nm, measured at 530 nm.

    7. The halide perovskite compound of claim 1, comprising increased air stability as compared to a control compound A.sub.2M(IV)X.sub.6 without the crown ether and comprising the same A, M, and X as the halide perovskite compound.

    8. The halide perovskite compound of claim 7, wherein the air stability of the halide perovskite compound is increased by about 1 hour to about 3 days as compared to the control compound.

    9. A halide perovskite compound according to the formula: (crown ether@A)M(II)X.sub.4 or (crown ether@A)M(III)X.sub.5, wherein the M(II) is at least one divalent metal cation, the M(III) is at least one trivalent metal cation, the X is at least one halide anion, and the crown ether@A is at least one alkali metal-bound crown ether formed between an alkali metal cation A and oxygen atoms of a crown ether.

    10. The halide perovskite compound of claim 9, wherein the M(II) is one or more of Mn.sup.2+ and Ni.sup.2+; the M(III) is Sb.sup.3+; the X is one or more of Cl.sup. and Br.sup.; the crown ether is 18-Crown-6 (18C6); and the A is Ba.sup.2+.

    11. The halide perovskite compound of claim 9, wherein the halide perovskite compound is (18C6@Ba)MnBr.sub.4 or (18C6@Ba)SbCl.sub.5.

    12. The halide perovskite compound of claim 9, comprising at least one of (i) a structural unit formed by one [crown ether@A].sup.2+ and one [M(II)X.sub.4].sup.2 or [M(III)X.sub.5].sup.2, (ii) a linear chain structure comprising a plurality of the structural unit, and (iii) a hexagonal or rhombohedral crystal structure comprising the plurality of the structural unit, wherein the [crown ether@A].sup.2+ is a free charged form of the crown ether@A, the [M(II)X.sub.4].sup.2 is a free charged form of the M(II)X.sub.4, and the [M(III)X.sub.5].sup.2 is a free charged form of the M(III)X.sub.5.

    13. The halide perovskite compound of claim 9, comprising greater photoluminescence quantum yield (PLQY) as compared to a control compound AM(II)X.sub.4 or AM(III)X.sub.5 without the crown ether and comprising the same A, M(II) or M(III), and X as the halide perovskite compound.

    14. The halide perovskite compound of claim 13, wherein the PLQY of the halide perovskite compound is greater than 80% under excitation at 449 nm, measured at 513 nm.

    15. The halide perovskite compound of claim 9, comprising increased air stability as compared to a control compound AM(II)X.sub.4 or AM(III)X.sub.5 without the crown ether and comprising the same A, M(II) or M(III), and X as the halide perovskite compound.

    16. A method of generating a halide perovskite compound, the method comprising: dissolving (i) a metal halide and (ii) an alkali metal halide and a crown ether, or an alkali metal-bound crown ether, in an organic solvent to provide a precursor solution, wherein the metal halide makes contact with at least one of the alkali metal, the crown ether, and the alkali metal-bound crown ether in the precursor solution; and contacting the organic solvent with an anti-solvent, wherein the halide perovskite compound crystalizes from the precursor solution.

    17. The method of claim 16, comprising at least one of wherein the organic solvent comprises N, N-Dimethylformamide (DMF) or acetonitrile (ACN), and wherein the anti-solvent comprises diethyl ether (DEE).

    18. The method of claim 16, wherein (i) the metal halide and (ii) the alkali metal and the crown ether, or the alkali metal-bound crown ether, are dissolved in the organic solvent at about 60-100 C.

    19. The method of claim 16, wherein the generated halide perovskite compound is free of impurities.

    20. A halide perovskite compound or a color luminescent composition comprising the halide perovskite compound generated by the method of claim 16.

    Description

    BRIEF DESCRIPTION OF THE DRAWINGS

    [0031] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

    [0032] FIG. 1 depicts supramolecular assembly strategy from the [M(IV)X.sub.6].sup.2 octahedron to (18C6@A).sub.2M(IV)X.sub.6. The dissolved alkali metal cation (A.sup.+) and [M(IV)X.sub.6].sup.2 octahedron self-assemble into a dumbbell-shaped structural unit with crown ethers like 18-Crown-6 (18C6). The solution-dispersed (18C6@A).sub.2M(IV)X.sub.6 dumbbell structural units can further assemble into a rhombohedral-packing single crystal. The dark-field optical microscopy image shows single crystals of (18C6@Cs).sub.2Te(IV)Cl.sub.6.

    [0033] FIGS. 2A-2D depict evidence of the formation of the (18C6@A).sub.2M(IV)X.sub.6 dumbbell structural unit in solution. The composition of (18C6@Cs).sub.2TeBr.sub.6 is applied as an illustrating example for the dumbbell structural unit, and ACN (ACN-d.sub.3 for NMR) is used as the solvent. FIG. 2A depicts .sup.1H NMR spectra for (18C6@Cs).sub.2TeBr.sub.6 solution and the control groups are (18C6@Cs)Br and 18C6 dissolved in solution. FIG. 2B depicts .sup.79Br NMR spectra for (18C6@Cs).sub.2TeBr.sub.6 solution and the control groups are Cs.sub.2TeBr.sub.6 and CsBr dissolved in solution. FIG. 2C depicts .sup.133Cs NMR spectra for (18C6@Cs).sub.2TeBr.sub.6 solution and the control groups are (18C6@Cs)Br, Cs.sub.2TeBr.sub.6, and CsBr dissolved in solution. FIG. 2D depicts UV-vis spectral comparison of (18C6@Cs).sub.2TeBr.sub.6 solution and Cs.sub.2TeBr.sub.6 dissolved in ACN solution.

    [0034] FIGS. 3A-3D depict synthetic tunability of the crown ether supramolecular approach. The four arrows represent the four dimensionalities in tuning the dumbbell structural unit from the initial (18C6@Cs).sub.2TeCl.sub.6 structural unit. FIG. 3A depicts that seven tetravalent octahedral cations can be applied, including transition metal cations such as Zr.sup.4+, Ir.sup.4+, and Pt.sup.4+, basic metal cations such as Sn.sup.4+, metalloid cations such as Te.sup.4+, nonmetal cations such as Se.sup.4+, and lanthanide cations such as Ce.sup.4+. FIG. 3B depicts tuning the halide anion from Cl.sup. to Br.sup. to I.sup. and the optical images are the powders of (18C6@Cs).sub.2TeX.sub.6 (X=Cl.sup., Br.sup., I.sup.) under ambient light. FIG. 3C depicts modifying the alkali metal cation coupled with 18C6 from Cs.sup.+ to Rb.sup.+ to K.sup.+ and the optical images are the powders of (18C6@A).sub.2TeCl.sub.6 dispersed in an anti-solvent under 365 nm UV lamp excitation. FIG. 3D depicts varying the size of the crown ether from 18C6 to 21C7.

    [0035] FIGS. 4A-4F depict systematic structural analysis of the family of (18C6@A).sub.2M(IV)X.sub.6 crystals. FIG. 4A depicts comparison of PXRD patterns by tuning the octahedron center element (M) in (18C6@A).sub.2M(IV)Cl.sub.6 (for M=Ce and Zr and A=Cs; for M=Pt, Ir, Se, Sn, and Te and A=K). FIG. 4C depicts comparison of PXRD patterns by changing the halide atom (X) in (18C6@Cs).sub.2TeX.sub.6. FIG. 4E depicts comparison of PXRD patterns by varying the alkali metal atom (A) in (18C6@A).sub.2TeCl.sub.6. FIGS. 4B, 4D, and 4F depict analysis of the geometric parameters of the dumbbell structural units: FIG. 4B depicts MCl bond length comparison of the structures with different octahedron center elements. FIG. 4D depicts that the MX bond length increases with larger X. FIG. 4F depicts that the height of the cone increases with larger A, while the diameter of the cone is insensitive to the change of A.

    [0036] FIGS. 5A-5D depict optoelectronic tunability of the crown ether supramolecular approach. FIG. 5A depicts normalized UV-vis absorption spectra of (18C6@A).sub.2M(IV)Cl.sub.6 (M=Sn.sup.4+, Te.sup.4+, Ce.sup.4+, and Ir.sup.4+) crystals. FIG. 5B depicts normalized UV-vis absorption spectra of (18C6@Cs).sub.2TeX.sub.6 (X=Cl.sup., Br.sup., and I.sup.) crystals. FIG. 5C depicts normalized UV-vis absorption spectra of [TeBr.sub.6].sup.2 octahedra under four different packing geometries. FIG. 5D depicts normalized PL spectra of (18C6@A).sub.2TeCl.sub.6 (A=Cs.sup.+, Rb.sup.+, and K.sup.+) crystals.

    [0037] FIG. 6 depicts photographs of the (18C6@Cs).sub.2TeBr.sub.6 single crystals grown from the anti-solvent crystallization method.

    [0038] FIGS. 7A-7F depict crystal structure of one typical example: (18C6@Cs).sub.2TeCl.sub.6. FIG. 7A is the top view and FIG. 7B is the side view of the atomic structure of the dumbbell (18C6@Cs).sub.2TeCl.sub.6 structural unit. FIG. 7C is the oblique view and FIG. 7D is the top view of (18C6@Cs).sub.2TeCl.sub.6 single crystal that is in rhombohedral R-3 space group. FIG. 7E is a dark field optical image and FIG. 7F is a scanning electron microscope image of (18C6@Cs).sub.2TeCl.sub.6 single crystal.

    [0039] FIG. 8 depicts a structure consists of two cones and one octahedron that simplifies the dumbbell structural unit.

    [0040] FIG. 9 depicts powder XRD of (18C6@Rb).sub.2TeI.sub.6 and (18C6@Cs).sub.2TeI.sub.6.

    [0041] FIG. 10 depicts powder XRD of (18C6@Cs).sub.2SnBr.sub.6, (18C6@Rb).sub.2SnBr.sub.6, and (18C6@K).sub.2SnBr.sub.6.

    [0042] FIG. 11 depicts thermogravimetric analysis (TGA) of (18C6@Cs).sub.2TeCl.sub.6, (18C6@Cs).sub.2TeBr.sub.6, and (18C6@Cs).sub.2SnCl.sub.6 under N.sub.2 atmosphere.

    [0043] FIG. 12 depicts thermogravimetric analysis (TGA) of (18C6@Cs).sub.2TeCl.sub.6, (18C6@Cs).sub.2TeBr.sub.6, and (18C6@Cs).sub.2SnCl.sub.6 under N.sub.2 atmosphere.

    [0044] FIG. 13 depicts Raman spectrum of Cs.sub.2TeCl.sub.6.

    [0045] FIG. 14 depicts normalized low-frequency Raman spectra of (18C6@A).sub.2TeCl.sub.6 (A=Cs.sup.+, Rb.sup.+, K.sup.+) crystals.

    [0046] FIG. 15 depicts Raman spectra of (18C6@A).sub.2TeBr.sub.6 (A=K.sup.+, Rb.sup.+, Cs.sup.+).

    [0047] FIG. 16 depicts Raman spectra of (18C6@A).sub.2SnCl.sub.6 (A=K.sup.+, Rb.sup.+, Cs.sup.+).

    [0048] FIG. 17 depicts Raman spectra of (18C6@A).sub.2SnBr.sub.6 (A=K.sup.+, Rb.sup.+, Cs.sup.+).

    [0049] FIGS. 18A-18C depict single crystal XRD characterization of 21C7 assembled crystals. FIG. 18A depicts the structure of the (21C7@Cs).sub.2TeBr.sub.6 fundamental building block. FIG. 18B depicts crystal structure of (21C6@Cs).sub.2TeBr.sub.6 viewed from the a axis. FIG. 18C depicts oblique view of the (21C7@Cs).sub.2TeBr.sub.6 single crystal structure. 21C7 molecules have been omitted for better demonstration of the packing geometry of the octahedra.

    [0050] FIG. 19 depicts powder X-ray diffraction pattern of (21C7@Cs).sub.2TeX.sub.6 (X=Br.sup., I.sup.).

    [0051] FIG. 20 depicts dark field optical microscopy image of (21C7@Cs).sub.2TeBr.sub.6 single crystal.

    [0052] FIGS. 21A-21B depicts scanning electron microscopy (SEM) image of the (21C7@Cs).sub.2TeBr.sub.6 single crystal. FIG. 21A provides a top view and FIG. 21B provides a side view.

    [0053] FIG. 22 depicts an optical image of (18C6@Cs).sub.2TeBr.sub.6 and Cs.sub.2TeBr.sub.6 powders. (18C6@Cs).sub.2TeBr.sub.6 has an orange color, while Cs.sub.2TeBr.sub.6 has a red color.

    [0054] FIG. 23 depicts normalized UV-vis absorption spectra and photoluminescence spectra of (18C6@A).sub.2TeCl.sub.6 (A=K.sup.+, Rb.sup.+, Cs.sup.+) crystals.

    [0055] FIGS. 24A-24G depict two assemblies of the [HfBr.sub.6].sup.2 ionic octahedron. FIG. 24A depicts the rhombohedral unit cell and FIG. 24B depicts the dumbbell-shaped structural unit of (18C6@K).sub.2HfBr.sub.6.

    [0056] FIG. 24C depicts the Fm-3m unit cell [from the Open Quantum Materials Database (OQMD) and FIG. 24D depicts the isolated [HfBr.sub.6].sup.2 ionic octahedron building block of K.sub.2HfBr.sub.6. FIG. 24E depicts the PXRD patterns for synthesized (18C6@K).sub.2HfBr.sub.6 and K.sub.2HfBr.sub.6 powders and the calculated diffraction patterns. K.sub.2HfBr.sub.6 showed quite poor PXRD quality because of its poor stability during measurement. a.u., arbitrary unit. FIG. 24F depicts the structure and corresponding total pDOS of (18C6@K).sub.2HfBr.sub.6. FIG. 24G depicts the structure and corresponding total pDOS of K.sub.2HfBr.sub.6. When [HfBr.sub.6].sup.2 octahedra were assembled in the supramolecular approach, the dispersion of the bands decreased, and 18C6 contributed to the valence band (VB).

    [0057] FIGS. 25A-25E depict blue emission with near-unity PLQY (96.2%) from (18C6@K).sub.2HfBr.sub.6 powders and green emission with a PLQY of 82.7% from (18C6@K).sub.2ZrCl.sub.4Br.sub.2 powders. FIG. 25A depicts (18C6@K).sub.2HfBr.sub.6 powders under white lamp and 254-nm UV excitation. FIG. 25B depicts PL and PLE spectra of (18C6@K).sub.2HfBr.sub.6 powders. FIG. 25C depicts (18C6@K).sub.2ZrCl.sub.4Br.sub.2 powders under white lamp and 302-nm UV excitation. FIG. 25D depicts PL and PLE spectra of (18C6@K).sub.2ZrCl4Br2 powders. FIG. 25E depicts the CIE 1931 chromaticity diagram for the emission of (18C6@K).sub.2HfBr.sub.6 powders and (18C6@K).sub.2ZrCl.sub.4Br.sub.2 powders. B stands for the blue emission of (18C6@K).sub.2HfBr.sub.6, and G stands for the green emission of (18C6@K).sub.2ZrCl.sub.4Br.sub.2. The coordinates for the emission colors of (18C6@K).sub.2HfBr.sub.6 and (18C6@K).sub.2ZrCl.sub.4Br.sub.2 were (0.17438, 0.16922) and (0.30597, 0.41533), respectively.

    [0058] FIGS. 26A-26D depict photophysical analysis of (18C6@K).sub.2HfBr.sub.6 and (18C6@K).sub.2ZrCl.sub.4Br.sub.2. FIG. 26A depicts PL spectra of (18C6@K).sub.2HfBr.sub.6 powders at 4, 50, 100, 150, 210, and 293 K. FIG. 26B depicts FWHM of the PL spectra of (18C6@K).sub.2HfBr.sub.6 powders at different temperatures, with the orange and teal solid lines denoting the least-square fit to Eq. 1 at low (4 to 190 K) and high (190 to 293 K) temperature ranges, respectively. FIG. 26C depicts PLE spectroscopy of (18C6@K).sub.2HfBr.sub.6 powders. FIG. 26D depicts normalized PL decay curves of (18C6@K).sub.2ZrCl.sub.4Br.sub.2 and (18C6@K).sub.2HfBr.sub.6 single crystals.

    [0059] FIGS. 27A-27G depict solution processability and display application of highly emissive blue and green semiconductor inks. FIG. 27A depicts schematic illustrating the thin-film fabrication method and the display application. The inks were formed by mixing (18C6@K).sub.2HfBr.sub.6 or (18C6@K).sub.2ZrCl.sub.4Br.sub.2 powders and PS in DCM. Thin films were obtained by drop casting, and they demonstrated programmable display capability. DMD, digital micromirror device. FIG. 27B depicts (18C6@K).sub.2HfBr.sub.6/PS-DCM ink under white light and 254-nm UV lamp excitation. FIG. 27C depicts (18C6@K).sub.2ZrCl.sub.4Br.sub.2/PS-DCM ink under white light and 302-nm lamp excitation. FIG. 27D depicts (18C6@K).sub.2HfBr.sub.6/PS composite thin film under white light and 254-nm UV excitation. FIG. 27E depicts (18C6@K).sub.2ZrCl.sub.4Br.sub.2/PS composite thin film under white light and 302-nm UV excitation. The scale bars for FIGS. 27B and 27E are 1 cm. The PLQYs of all samples are shown in the photos. FIG. 27F depicts image of the Cal logo blue emission on the (18C6@K).sub.2HfBr.sub.6/PS composite thin film. FIG. 27G depicts snapshots of a video showing the alphabet, A to Z, with 0.1 s per letter on the (18C6@K).sub.2HfBr.sub.6/PS composite thin film. The scale bars for FIGS. 27F and 27G are 3 mm and 4 mm, respectively.

    [0060] FIGS. 28A-28G depict implementation of the blue-green dual-color 3D printing. FIG. 28A depicts schematic illustrating the multimaterial 3D printing process. FIG. 28B depicts two 3D-printed light-emitting Eiffel Towers under white light excitation. FIG. 28C depicts two 3D-printed light-emitting Eiffel Towers under 254-nm UV excitation. FIG. 28D depicts a dual-color-emitting Eiffel Tower under 254-nm UV excitation. FIGS. 28E-28H depict conformal and twisted octet trusses with varying hierarchical structures and geometric shapes, including cuboctahedron, tetrakaidecahedron, and Menger sponge structures, with the blue and green emitters or their combinations, respectively. These printed architectures were photoexcited at 254 nm. The scale bars for FIGS. 28B-28G are 5 mm. The scale bar for the zoom-in image of FIG. 28E is 0.6 mm. The scale bar for FIG. 28H is 4 mm.

    [0061] FIG. 29 depicts Raman spectroscopy of the K.sub.2HfBr.sub.6 powders measured in inert atmosphere. The asymmetric bending mode (T.sub.2g) and symmetric stretching mode (A.sub.1g) of the Oh-symmetric vibrating [HfBr.sub.6].sup.2 are identified. The baseline appears to be noisy due to the low Raman intensity of the powders sample and the signal loss coming from the cover glass on the inert-atmosphere sample holder.

    [0062] FIGS. 30A-30B depict crystal structure of (18C6@K).sub.2ZrBr.sub.6 determined by single crystal x-ray diffraction. FIG. 30A depict the unit cell viewed along the c axis direction. FIG. 30B depict the unit cell viewed along the direction perpendicular to the c axis.

    [0063] FIG. 31 depicts Normalized PXRD patterns of (18C6@K).sub.2ZrBr.sub.6 and K.sub.2ZrBr.sub.6 powders.

    [0064] FIG. 32A depicts band structure and corresponding total partial density of states (pDOS) of (18C6@K).sub.2ZrBr.sub.6. FIG. 32B depicts band structure and corresponding pDOS of K.sub.2ZrBr.sub.6.

    [0065] FIGS. 33A-33F depict PLQY measurement of (18C6@K).sub.2ZrBr.sub.6 powders at 275-nm excitation. The black line is the measurement of the sample, and the red line is the measurement of the blank sample holder. FIGS. 33A-33C depict three measurements from sample batch 1. FIGS. 33D-33F depict three measurements from sample batch 2.

    [0066] FIGS. 34A and 34B depict PLQY measurement of K.sub.2HfBr.sub.6 powders at 275-nm excitation. In FIG. 34A, the black line is the measurement of the sample, and the red line is the measurement of the blank sample holder. FIG. 34B depicts a zoom-in spectra of FIG. 34A to better show the shape of the sample spectrum.

    [0067] FIG. 35 depicts PL spectrum of K.sub.2HfBr.sub.6 powders at 275-nm excitation. The spectrum appears to be noisy due to the poor stability of K.sub.2HfBr.sub.6 powders in the air, and the therefore high measuring speed.

    [0068] FIG. 36 depicts the CIE 1931 chromaticity diagram for the emissions of K.sub.2HfBr.sub.6 powders and (18C6@K).sub.2HfBr.sub.6 powders. The coordinates for the emission color of K.sub.2HfBr.sub.6 were (0.21603, 0.24368), and the coordinates for the emission color of (18C6@K).sub.2HfBr.sub.6 were (0.17438, 0.16922).

    [0069] FIG. 37 depicts PL spectrum of (18C6@K).sub.2ZrBr.sub.6 powders at 290-nm excitation.

    [0070] FIG. 38 depicts PL spectrum of K.sub.2ZrBr.sub.6 powders at 290-nm excitation.

    [0071] FIGS. 39A-39B depict PLQY measurement of (18C6@K).sub.2ZrBr.sub.6 powders at 290-nm excitation.

    [0072] In FIG. 39A, the black line is the measurement of the sample, and the red line is the measurement of the blank sample holder. FIG. 39B depicts zoom-in spectra of FIG. 39A to better show the shape of the sample spectrum.

    [0073] FIGS. 40A-40B depict PLQY measurement of K.sub.2ZrBr.sub.6 powders at 290-nm excitation. In FIG. 40A, the black line is the measurement of the sample, and the red line is the measurement of the blank sample holder. FIG. 40B depicts zoom-in spectra of FIG. 40A to better show the shape of the sample spectrum.

    [0074] FIG. 41 depicts the CIE 1931 chromaticity diagram for the emissions of (18C6@K).sub.2ZrBr.sub.6 powders and (18C6@K).sub.2ZrCl.sub.4Br.sub.2 powders. The coordinates for the emission color of (18C6@K).sub.2ZrBr.sub.6 powders were (0.37601, 0.45927), and the coordinates for the emission color of (18C6@K).sub.2ZrCl.sub.4Br.sub.2 powders were (0.30597, 0.41533).

    [0075] FIG. 42 depicts Normalized PL spectra of different C1/Br ratio (18C6@K).sub.2ZrCl.sub.xBr.sub.6-x powders.

    [0076] FIG. 43 depicts the CIE 1931 chromaticity diagram for the emissions of powders of (A) (18C6@K).sub.2ZrBr.sub.6, (B) (18C6@K).sub.2ZrCl.sub.3Br.sub.3, (C) (18C6@K).sub.2ZrCl.sub.4Br.sub.2, and (D) (18C6@K).sub.2ZrCl.sub.4.5Br.sub.1.5. The CIE coordinates were (0.37601, 0.45927), (0.29979, 0.40829), (0.30597, 0.41533), and (0.32101, 42682), respectively.

    [0077] FIGS. 44A-44D depict PLQY measurement of (18C6@K).sub.2ZrCl.sub.4Br.sub.2 powders at 295-nm excitation. The black line is the measurement of the sample, and the red line is the measurement of the blank sample holder. FIGS. 44A and 44B depict two measurements from sample batch 1. FIGS. 44C and 44D depict two measurements from sample batch 2.

    [0078] FIG. 45A depicts PLQY measurements of (18C6@K).sub.2ZrCl.sub.3Br.sub.3 powder at 295-nm excitation. FIG. 45B depicts PLQY measurements of (18C6@K).sub.2ZrCl4.5Br.sub.1.5 powder at 295-nm excitation. The black line is the measurement of the sample, and the red line is the measurement of the blank sample holder.

    [0079] FIGS. 46A and 46B depict crystal structure of (18C6@K).sub.2ZrCl.sub.4Br.sub.2 determined by single crystal x-ray diffraction. FIG. 46A depicts the unit cell viewed along the c axis direction. FIG. 46B depicts the unit cell viewed along the direction perpendicular to the c axis. The molar ratio of Cl/Br was determined to be 4.3:1.7 according to the electron density calculation.

    [0080] FIG. 47 depicts SEM-EDX results of a (18C6@K).sub.2ZrCl.sub.4Br.sub.2 single crystal, including SEM image, EDX elemental mapping, EDX spectrum and the corresponding atomic percentages. The EDX spectrum shows nonoverlapping characteristic x-ray signals for K L.sub.1 (0.260 keV), K K.sub.1 (3.314 keV), Zr L.sub.1 (2.042 keV), Cl K.sub.1 (2.622 keV), Br L.sub.1,2 (1.480 keV). Integration of the K, Zr, Cl, and Br emission lines confirmed the atomic ratio of K/Zr/Cl/Br to be approximately 2:1:4:2. The scale bars are 25 m.

    [0081] FIG. 48 depicts PXRD of (18C6@K).sub.2ZrCl.sub.4Br.sub.2 powders.

    [0082] FIG. 49 depicts PXRD comparison of (18C6@K).sub.2ZrCl.sub.4Br.sub.2 powders and (18C6@K).sub.2ZrBr.sub.6 powders at 2Theta values between 7 to 15 degrees. Both the (101) and (110) diffraction peaks of (18C6@K).sub.2ZrCl.sub.4Br.sub.2 were shifted to larger degree values.

    [0083] FIG. 50 depicts Gaussian peak fitting of the PL spectrum of (18C6@K).sub.2HfBr.sub.6 powders measured at 4 K. The shoulder peak at 2.3 eV came from the 0.6 atomic % Zr impurity in Hf.

    [0084] FIG. 51 depicts Raman spectroscopy of (18C6@K).sub.2HfBr.sub.6 powders. Three distinct Raman-active modes including the low-frequency asymmetric bending mode T.sub.2g, the asymmetric stretching mode E.sub.g, the high-frequency symmetric stretching mode A.sub.1g corresponding to the Oh-symmetric vibrating [HfBr.sub.6].sup.2.

    [0085] FIG. 52 depicts PLE spectroscopy of (18C6@K).sub.2ZrBr.sub.6 powders.

    [0086] FIGS. 53A-53D depict photodegradation responses of (18C6@K).sub.2HfBr.sub.6 and (18C6@K).sub.2ZrCl.sub.4Br.sub.2 powders. The powders were dispersed in toluene-d.sub.8, placed in an argon-filled UV cuvette, and subjected to irradiation with a xenon lamp at 62 mW/cm.sup.2 and 35 C. FIG. 53A depicts PL spectra of the (18C6@K).sub.2HfBr.sub.6 sample measured at five different times during the continuous irradiation. FIG. 53B depicts the PL intensity decay of the (18C6@K).sub.2HfBr.sub.6 sample over irradiation time. FIG. 53C depicts PL spectra of the (18C6@K).sub.2ZrCl.sub.4Br.sub.2 sample measured at six different times during the continuous irradiation. FIG. 53D depicts the PL intensity decay of the (18C6@K).sub.2ZrCl.sub.4Br.sub.2 sample over irradiation time.

    [0087] FIG. 54 depicts PL spectra comparison of (18C6@K).sub.2HfBr.sub.6/PS composite film, (18C6@K).sub.2HfBr.sub.6 in DCM ink, and (18C6@K).sub.2HfBr.sub.6 powders.

    [0088] FIGS. 55A-55B depict PLQY measurement of (18C6@K).sub.2HfBr.sub.6/PS in DCM ink at 275-nm excitation. In FIG. 55A, the black line is the measurement of the sample, and the red line is the measurement of the PS in DCM control ink. FIG. 55B depicts zoom-in spectra of FIG. 55A to better show the shape of the sample spectrum.

    [0089] FIG. 56A depicts UV-vis absorption spectra of DCM solvent. FIG. 56B depicts UV-vis absorption spectra of PS thin film.

    [0090] FIGS. 57A-57B depict PLQY measurement of (18C6@K).sub.2ZrCl.sub.4Br.sub.2/PS in DCM ink at 295-nm excitation. In FIG. 57A, the black line is the measurement of the sample, and the red line is the measurement of the PS in DCM control ink. FIG. 57B depicts zoom-in spectra of (A) to better show the shape of the sample spectrum.

    [0091] FIG. 58 depicts PXRD comparison of (18C6@K).sub.2HfBr.sub.6/PS composite film, PS film, and (18C6@K).sub.2HfBr.sub.6 powders.

    [0092] FIG. 59 depicts PXRD of (18C6@K).sub.2ZrCl.sub.4Br.sub.2/PS composite film.

    [0093] FIGS. 60A-60F depicts SEM imaging of the powders and thin films. FIGS. 60A and 60B depict (18C6@K).sub.2HfBr.sub.6 powders. FIGS. 60C and 60D depict top views of the surface of the pure PS film. FIGS. 60E and 60F depict top views of the surface of the (18C6@K).sub.2HfBr.sub.6/PS composite film. The scale bars are 20 m for FIGS. 60A, 60C, and 60E, and 5 m for FIGS. 60B, 60D, and 60F.

    [0094] FIGS. 61A-61D depict SEM imaging of the thin film cross sections. FIGS. 61A and 61B depict (18C6@K).sub.2HfBr.sub.6/PS composite film. FIGS. 61C and 61D depict pure PS film. The scale bars are 50 m for FIGS. 61A and 61C, and 5 m for FIGS. 61B and 61D.

    [0095] FIG. 62 depicts PL spectra comparison of (18C6@K).sub.2ZrCl.sub.4Br.sub.2/PS composite film, (18C6@K).sub.2ZrCl.sub.4Br.sub.2 in DCM ink, and (18C6@K).sub.2ZrCl.sub.4Br.sub.2 powders.

    [0096] FIGS. 63A and 63B depict PLQY measurement of (18C6@K).sub.2HfBr.sub.6/PS composite film at 275-nm excitation. In FIG. 63A, the black line is the measurement of the sample, and the red line is the measurement of the PS control. FIG. 63B depicts zoom-in spectra of FIG. 63A to better show the shape of the sample spectrum.

    [0097] FIGS. 64A and 64B depict PLQY measurement of (18C6@K).sub.2ZrCl.sub.4Br.sub.2/PS composite film at 295-nm excitation. In FIG. 64A, the black line is the measurement of the sample, and the red line is the measurement of the PS control. FIG. 64B depicts zoom-in spectra of FIG. 64A to better show the shape of the sample spectrum.

    [0098] FIGS. 65A-65D depict blue- and green-emitting films after one-month storage in the air. FIG. 65A depicts (18C6@K).sub.2HfBr.sub.6/PS composite film under white lamp. FIG. 65B depicts (18C6@K).sub.2HfBr.sub.6/PS composite film under 254-nm UV lamp. FIG. 65C depicts (18C6@K).sub.2ZrCl.sub.4Br.sub.2/PS composite film under white lamp. FIG. 65D depicts (18C6@K).sub.2ZrCl.sub.4Br.sub.2/PS composite film under 302-nm UV lamp.

    [0099] FIG. 66A depicts UV-vis absorption spectrum of solid PEGDA resin. FIG. 66B depicts PL measurement of solid PEGDA resin. FIG. 66C depicts PL measurement of (18C6@K).sub.2HfBr.sub.6/PEGDA composite film. FIG. 66D depicts PL measurement of (18C6@K).sub.2ZrCl.sub.4Br.sub.2/PEGDA composite film.

    [0100] FIG. 67 depicts the CIE 1931 chromaticity diagram for the emissions of (18C6@K).sub.2HfBr.sub.6 powders and (18C6@K).sub.2HfBr.sub.6/PEGDA composite film. The coordinates for the emission color of (18C6@K).sub.2HfBr.sub.6 powders were (0.17438, 0.16922), and the coordinates for (18C6@K).sub.2HfBr.sub.6/PEGDA composite film were (0.20443, 0.23635).

    [0101] FIG. 68 depicts the CIE 1931 chromaticity diagram for the emissions of (18C6@K).sub.2ZrCl.sub.4Br.sub.2 powders and (18C6@K).sub.2ZrCl.sub.4Br.sub.2/PEGDA composite. The coordinates for the emission color of (18C6@K).sub.2ZrCl.sub.4Br.sub.2 powders were (0.30597, 0.41533), and the coordinates for the emission color of (18C6@K).sub.2ZrCl.sub.4Br.sub.2/PEGDA composite film were (0.28378, 0.37125).

    [0102] FIG. 69A depicts 3D-printed twisted octet trusses architecture with (18C6@K).sub.2HfBr.sub.6 and (18C6@K).sub.2ZrCl.sub.4Br.sub.2 powders embedded under white lamp excitation. FIG. 69B depicts 3D-printed twisted octet trusses architecture with (18C6@K).sub.2HfBr.sub.6 and (18C6@K).sub.2ZrCl.sub.4Br.sub.2 powders embedded under 254-nm UV lamp excitation. The scale bars are 5 mm.

    [0103] FIG. 70A depicts 3D-printed conformal octet trusses architecture with (18C6@K).sub.2HfBr.sub.6 and (18C6@K).sub.2ZrCl.sub.4Br.sub.2 powders embedded under white lamp excitation. FIG. 70B depicts 3D-printed conformal octet trusses architecture with (18C6@K).sub.2HfBr.sub.6 and (18C6@K).sub.2ZrCl.sub.4Br.sub.2 powders embedded under 254-nm UV lamp excitation. FIG. 70C depicts regional zoom-in image of the structure under 254-nm UV lamp excitation. The scale bars for FIGS. 70A and 70B are 5 mm. The scale bar for FIG. 70C is 2 mm.

    [0104] FIGS. 71A, 71C, 71E, and 71G depict 3D-printed architectures with (18C6@K).sub.2HfBr.sub.6 powders embedded as Geometric shapes of cuboctahedron, tetrakaidecahedron, octet truss, and Menger sponge under white lamp, respectively. FIGS. 71B, 71D, 71F, and 7111 depicts the corresponding 3D-printed architectures under 254-nm UV lamp excitation. The scale bars are 2 mm.

    [0105] FIG. 72A depicts a photo of a group of the 3D-printed architectures under white lamp excitation. FIG. 72B depicts a photo of a group of the 3D-printed architectures under 254-nm UV lamp excitation. The scale bars are 5 mm.

    [0106] FIG. 73 depicts the quantum dot LED (QLED) display structure diagram. Quantum dots can convert the blue light into red and green light, creating the RGB pixels.

    [0107] FIGS. 74A-74D depict Crystal structure of the green emitter (18C6@Ba)MnBr.sub.4. FIG. 74A depicts the basic structural unit of (18C6@Ba)MnBr.sub.4. FIG. 74B depicts the 1D linear chain structure formed by connecting the basic structural unit. FIG. 74C depicts the top view and FIG. 74D depicts the side view of the unit cell of the (18C6@Ba)MnBr.sub.4 single crystal.

    [0108] FIGS. 75A-75C depict photoluminescence properties of (18C6@Ba)MnBr.sub.4. FIG. 75A depicts photoluminescence (PL) and photoluminescence excitation (PLE) spectra of (18C6@Ba)MnBr.sub.4. powders with 365-nm excitation. The PLQY was determined to be 82.1%. The inset image is the green emission of a (18C6@Ba)MnBr.sub.4 crystal under confocal microscope. FIG. 75B depicts the CIE 1931 chromaticity diagram for the emission of (18C6@Ba)MnBr.sub.4 powders. The coordinates for the emission color of was (0.13713, 0.66309). FIG. 75C depicts 2D PLE spectroscopy of (18C6@Ba)MnBr.sub.4 powders.

    [0109] FIGS. 76A-76F depict the crystal structure and optical properties of (18C6@Ba)SbCl.sub.5. FIG. 76A depicts the (18C6@Ba)SbCl.sub.5 asymmetric unit. FIG. 76B depicts the linear infinite 1D chain of repeating (18C6@Ba)SbCl.sub.5 asymmetric units. FIG. 76C depicts the rhombohedral unit cell of the (18C6@Ba)SbCl.sub.5 single crystal viewed from the perpendicular direction of the c axis. FIG. 76D depicts the rhombohedral unit cell of the (18C6@Ba)SbCl.sub.5 single crystal viewed along the direction of the c axis. FIG. 76E depicts the PL spectrum of (18C6@Ba)SbCl.sub.5 with 375-nm excitation. FIG. 76F depicts confocal microscope images of (18C6@Ba)SbCl.sub.5 under white light and 375-nm excitation. The scale bar is 20 m.

    DETAILED DESCRIPTION

    [0110] Reference will now be made in detail to some specific examples of the invention including the best modes contemplated by the inventors for carrying out the invention. Examples of these specific embodiments are illustrated in the accompanying drawings. While the invention is described in conjunction with these specific embodiments, it will be understood that it is not intended to limit the invention to the described embodiments. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

    [0111] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. Particular example embodiments of the present invention may be implemented without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention.

    [0112] Various techniques and mechanisms of the present invention will sometimes be described in singular form for clarity. However, it should be noted that some embodiments include multiple iterations of a technique or multiple instantiations of a mechanism unless noted otherwise.

    [0113] The terms about or approximate and the like are synonymous and are used to indicate that the value modified by the term has an understood range associated with it, where the range can be 20%, 15%, 10%, 5%, or 1%. The terms substantially and the like are used to indicate that a value is close to a targeted value, where close can mean, for example, the value is within 80% of the targeted value, within 85% of the targeted value, within 90% of the targeted value, within 95% of the targeted value, or within 99% of the targeted value.

    [0114] As used herein with respect to a parameter, the term decreased or decreasing or decrease or reduced or reducing or reduce or lower refers to a detectable (such as at least about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or 100%) negative change in the parameter from a comparison control, such as an established normal or reference level of the parameter, or an established standard control. Accordingly, the terms decreased, reduced, and the like encompass both a partial reduction and a complete reduction compared to a control.

    [0115] As used herein with respect to a parameter, the term increased or increasing or increase or enhanced or enhancing or enhance or greater refers to a detectable (such as at least about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, 200%, 300%, 400%, 500%, 600%, 700%, 800%, 900%, or 1000%) positive change in the parameter from a comparison control, such as an established normal or reference level of the parameter, or an established standard control.

    A. Supramolecular Assembly of Halide Perovskites

    [0116] Emission with high photoluminescence quantum yield (PLQY) is at the forefront of solid-state lighting and color display research. Covalent semiconductors such as GaN require high purity to prevent rapid nonradiative recombination at crystal structure defects and rely on solid-state synthesis at elevated temperatures near 1000 C. As an alternative to covalent semiconductors, ionic halide perovskites have received attention given their high optical absorption coefficient, tunable bandgap, high defect tolerance, and efficient photo- and electroluminescence. For example, the blue and green emissive colloidal CsPbCl.sub.xBr.sub.3-x quantum dots have exhibited PLQY values of 80%. In addition, low-dimensional halide perovskites like the n=1 Ruddlesden-Popper phase (C.sub.6H.sub.5CH.sub.2NH.sub.3).sub.2PbBr.sub.4 show blue emission with a PLQY of 79%. Despite the notable optoelectronic properties of lead-based halide perovskites, the toxicity of lead and the complex colloidal synthesis complicate large scale applications. Moreover, suitable ligands are still needed to prevent aggregation of these low-dimensional nanostructures during use.

    [0117] The structural diversity and tunable optoelectronic properties of halide perovskites originate from the rich chemistry of metal halide ions, such as metal halide ionic octahedron [MX.sub.6].sup.n and metal halide ionic tetrahedron [MX.sub.4].sup.n, where M is a metal cation such as Te.sup.4+, Sn.sup.4+, Pt.sup.2+, Se.sup.3+, Ir.sup.4+, Zr.sup.4+, Hf.sup.4+, Ce.sup.4+, and Mn.sup.2+, and X is a halide such as Cl.sup., Br.sup., and I.sup.. The properties of the extended perovskite solids are dictated by the assembly, connectivity, and interaction of these halide perovskite units within the lattice environment. Hence, the ability to manipulate and control the assembly of the halide perovskite building blocks is paramount for constructing new perovskite materials. Provided herein is a systematic supramolecular strategy for the assembly of a metal halide anionic unit into a solid extended network.

    [0118] Interaction of alkali metal-bound crown ethers with the metal halide anionic unit such as the [M(IV)X.sub.6].sup.2 octahedron, the [M(II)X.sub.4].sup.2 tetrahedron, or [M(III)X.sub.5].sup.2 octahedron can result in a structurally and optoelectronically tunable dumbbell structural unit or a linear chain in solution. Single crystals with diverse packing geometries and symmetries form as the solid assembly of this new supramolecular building block. The supramolecular assembly route provided herein introduces a new general strategy for designing halide perovskite structures with potentially new optoelectronic properties.

    [0119] The crown ether-assisted supramolecular approach can stabilize halide perovskite (such as [M(IV)X.sub.6].sup.2, [M(II)X.sub.6].sup.2, and [M(III)X.sub.5].sup.2 (M(IV)=tetravalent metal cation, M(II)=divalent metal cation, M(III)=trivalent metal cation, X=halide anion) emission centers in crystals with superior emission properties. The compounds, compositions, and methods provided herein have at least the following advantages over other materials having these emission centers: [0120] (1) The PLQY of the supramolecular assembled solids can be improved. For example, (18-Crown-6@K).sub.2HfBr.sub.6 can achieve blue emission with a near-unity PLQY value of 96.22%, while the K.sub.2HfBr.sub.6 has a PLQY of around 40%. (18-Crown-6@K).sub.2ZrCl.sub.4Br.sub.2 can achieve green emission with a PLQY value of 82.7%, while K.sub.2ZrBr.sub.6 has a PLQY of about 46%. [0121] (2) The emission has great tunability in terms of the emission color. Halide perovskite units with eight different tetravalent metal centers (Te, Sn, Pt, Ir, Zr, Hf, Ce, Se) for octahedra formation or Mn for tetrahedra formation, and all three halides (Cl, Br, I) can be stabilized. [M(II)X.sub.6].sup.2 and [M(III)X.sub.5].sup.2 adds further options for tunability. These options enable emission across the whole visible spectrum. [0122] (3) The synthetic condition is much more cost-effective and mild than the traditional alkali metal cation vacancy-ordered perovskites such as A.sub.2M(IV)X.sub.6, AM(II)X.sub.4, or AM(III)X.sub.5. All the compositions can be fabricated using polar organic solvents at 60-100 C., such as 80 C. In contrast, some metal cation vacancy-ordered perovskites, such as Cs.sub.2ZrBr.sub.6 and Cs.sub.2HfBr.sub.6, require high temperature (800 C.) solid-state synthesis. [0123] (4) The purity of the synthetic product is higher than the alkali metal cation vacancy-ordered perovskites. For example, (18-Crown-6@K).sub.2ZrBr.sub.6, (18-Crown-6@K).sub.2HfBr.sub.6, and (18-Crown-6@Ba)MnBr.sub.4 are very pure according to powder XRD measurements, whereas the synthesis of Cs.sub.2ZrBr.sub.6, Cs.sub.2HfBr.sub.6, or BaMnBr.sub.4 can result in non-negligible CsBr or BaBr.sub.2 impurities. [0124] (5) The air stability of the supramolecular assembled powders is improved. For example, Zr and Hf containing double perovskites are susceptible to moisture, but when they are assembled by crown ethers, the air stability increased from one hour to a few days.
    (i) Halide Perovskite Compound (Crown Ether@A).sub.2M(IV)X.sub.6

    [0125] A halide perovskite compound according to the formula: (crown ether@A).sub.2M(IV)X.sub.6 has the M(IV), which is at least one tetravalent metal cation; the X, which is at least one halide anion; and the crown ether@A, which is at least one alkali metal-bound crown ether formed between an alkali metal cation A and oxygen atoms of a crown ether, e.g., by electrostatic interaction. The (crown ether@A).sub.2M(IV)X.sub.6 can form an octahedral unit.

    [0126] The halide perovskite compound provided herein can be tunable by adjusting components, i.e., crown ether, A, M(IV), and X. For example, the M(IV) can be one or more of; Te.sup.4+, Sn.sup.4+, Pt.sup.2+, Se.sup.3+, Ir.sup.4+, Zr.sup.4+, Hf.sup.4+, and Ce.sup.4+; the X can be one or more of Cl.sup., Br.sup., and I.sup.; the crown ether can be one or more of 18-Crown-6 (18C6) and 21-Crown-7 (21C7); and/or the A can be one or more of Cs.sup.+, Rb.sup.+, and K.sup.+. For example, halide perovskite compound can be (18-Crown-6@K).sub.2HfBr.sub.6 or (18C6@K).sub.2ZrCl.sub.4Br.sub.2. For example, X6 can be any combination of Cl.sup., Br.sup., and I.sup., such as Cl.sub.6, Cl.sub.5Br, Cl.sub.4Br.sub.2, Cl.sub.3Br.sub.3, Cl.sub.2Br.sub.4, ClBr.sub.5, Br.sub.6, Cl.sub.5I, Cl.sub.4I.sub.2, Cl.sub.3I.sub.3, Cl.sub.2I.sub.4, ClI.sub.5, I.sub.6, Br.sub.5I, Br.sub.4I.sub.2, Br.sub.3I.sub.3, Br.sub.2I.sub.4, BrI.sub.5, Cl.sub.4BrI, Cl.sub.3Br.sub.2I, Cl.sub.3BrI.sub.2, Cl.sub.2Br.sub.3I, Cl.sub.2Br.sub.2I.sub.2, Cl.sub.2BrI.sub.3, ClBr.sub.4I, ClBr.sub.3I.sub.2, ClBr.sub.2I.sub.3, and ClBrI.sub.4.

    [0127] The halide perovskite compound can be (18 C6@Cs).sub.2M(IV)Cl.sub.6, wherein the M(IV) is Te.sup.4+, Sn.sup.4+, Pt.sup.2+, Se.sup.3+, Ir.sup.4+, Zr.sup.4+, Hf.sup.4+, or Ce.sup.4+. The halide perovskite compound can be (18C6@Cs).sub.2TeX.sub.6, wherein the X is Cl.sup., Br.sup., or I.sup.. The halide perovskite compound can be (18C6@A).sub.2TeCl.sub.6, wherein the A is Cs.sup.+, Rb.sup.+, or K.sup.+. The halide perovskite compound can be (Crown ether@Cs).sub.2TeCl.sub.6, wherein crown ether is 18C6 or 21C7. The halide perovskite compound can be (18 C6@K).sub.2M(IV)Cl.sub.6, wherein the M(IV) is Pt.sup.2+, Ir.sup.4+, Se.sup.3+, Sn.sup.4+, or Te.sup.4+.

    [0128] The halide perovskite compound can be (18C6@Cs).sub.2TeBr.sub.6 or (18C6@Cs).sub.2TeCl.sub.6.

    [0129] The halide perovskite compound can form a dumbbell-shaped structural unit formed by two [crown ether@A].sup.+s and one [M(IV)X.sub.6].sup.2, and/or a rhombohedral crystal structure of a plurality of the dumbbell-shaped structural units. The [crown ether@A].sup.+ is a free charged form of the crown ether@A, and the [M(IV)X.sub.6].sup.2 is a free charged form of the M(IV)X.sub.6. The halide perovskite compound (crown ether@A).sub.2M(IV)X.sub.6 can be in any form such as in powder, crystal, or solution. The halide perovskite compound (crown ether@A).sub.2M(IV)X.sub.6 can have higher purity as compared to a control compound (e.g., A.sub.2M(IV)X.sub.6 without the crown ether and comprising the same A, M(IV), and X as the halide perovskite compound (crown ether@A).sub.2M(IV)X.sub.6). The purity of the halide perovskite compound (crown ether@A).sub.2M(IV)X.sub.6 can be about 80%, 81%, 82%, 83%, 84%, 85%, 96%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 99.5%, or greater.

    [0130] The halide perovskite compound can have greater photoluminescence quantum yield (PLQY) as compared to a control compound A.sub.2M(IV)X.sub.6 without the crown ether and comprising the same A, M(IV), and X as the halide perovskite compound. For example, the PLQY of the halide perovskite compound can be about 80%, 81%, 82%, 83%, 84%, 85%, 96%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or greater. The PLQY can be measured at various excitation/emission wavelength, including under excitation at 275 nm and measured at 445 nm (blue light emission), or under excitation at 295 nm and measured at 530 nm (green light emission). For example, formula (18C6@K).sub.2HfBr.sub.6 has near-unity (96.2%) PLQY under excitation at 275 nm and measured at 445 nm. Formula (18C6@K).sub.2ZrCl.sub.4Br.sub.2 has green emission with 82.7% PLQY under excitation at 295 nm and measured at 530 nm.

    [0131] The halide perovskite compound provided herein can have increased air stability as compared to a control compound A.sub.2M(IV)X.sub.6 without the crown ether and comprising the same A, M, and X as the halide perovskite compound. In some embodiments, the air stability of the halide perovskite compound increased by about 1 hour to about 3 days as compared to the control compound.

    [0132] The optoelectronic properties of halide perovskites stem from the [MX.sub.6].sup.n (where M is a metal cation and X is a halide anion) fundamental building blocks in the crystal structure, and given the ionic nature and high chemical tunability of halide perovskite structures, different compositions and packing geometries of [MX.sub.6].sup.n could be explored for light-emission applications. The vacancy-ordered double perovskite(A.sub.2MX.sub.6 phase) has been proposed to incorporate tetravalent metal cation octahedra, such as [TeX.sub.6].sup.2, [SnX.sub.6].sup.2, and[PtX.sub.6].sup.2. Although the [PbX.sub.6].sup.4 octahedra are corner-shared in all three dimensions in the prototypical CsPbX.sub.3 structure, the [MX.sub.6].sup.2 octahedra in the A.sub.2MX.sub.6 phase are isolated because a vacancy occupies every other M site in the crystal structure. A few [MX.sub.6].sup.n emitters as well as some non-octahedral emitters with high PLQY (95%) have been identified with yellow emission, such as [SnX.sub.6].sup.4. However, emission of high PLQY with shorter wavelengths is still very rare. The isolated nature of the octahedra affects the optoelectronic properties in that the strong coupling of the exciton with lattice vibrations greatly lowers the energy level of the exciton and forces it into transient self-trapped exciton (STE) states with a range of self-trapped energy levels. As a result, the A.sub.2MX.sub.6 systems generally have broadband emissions with a large Stokes shift.

    [0133] Although the A.sub.2MX.sub.6 phase has been studied in various compositions, octahedra with Hf.sup.4+ or Zr.sup.4+ centers, especially [HfBr.sub.6].sup.2 and [ZrBr.sub.6].sup.2 octahedra, have rarely been the subject of research, even though they have interesting optoelectronic properties. Cs.sub.2HfBr.sub.6 crystals have a blue emission with the PL peak at 435 nm, and colloidal Cs.sub.2ZrBr.sub.6 nanocrystals have been demonstrated to have a green emission with a PLQY of 45%. There are several reasons why they are less explored. Theoretical and experimental studies have shown that the Hf.sup.4+ and Zr.sup.4+ metal centers are extremely air- and moisture sensitive in the A.sub.2MX.sub.6 phase. Their synthesis requires the vertical Bridgman-Stockbarger method at 1000 C. in sealed quartz ampoules. Finally, it is difficult to prepare high-purity samples that do not contain a secondary impurity, such as CsBr. Thus, a new methodology is needed for the synthesis of more stabilized and purer solid phases containing the [HfBr.sub.6].sup.2 or [ZrBr.sub.6].sup.2 octahedra. The halide perovskite compounds (crown ether@A).sub.2M(IV)X.sub.6 solves the foregoing problems.

    [0134] Described herein is the first demonstration of the stabilization of [M(IV)X.sub.6].sup.2 (M=tetravalent metal cation, X=halide anion) octahedra emission centers using a crown ether-assisted supramolecular approach. Compared with other methods to stabilize the [M(IV)X.sub.6].sup.2 octahedra, the described fabrication process is more cost-effective and facile. It is solution processable and easy to scale-up. The technical difficulty of organic solvent selection and anti-solvent selection were overcome to achieve 100% pure solids, including both single crystals and powders. N, N-Dimethylformamide (DMF) or acetonitrile (ACN) is used as the solvent to dissolve the alkali metal halide, tetravalent metal halide, and crown ether precursors. Diethyl ether (DEE) is applied as the anti-solvent to crystallize the solids out of the precursor solutions. The resulting halide perovskite compounds are free of any impurities and provide superior emission properties, with high PLQY. Halide perovskites comprising the formula (crown ether@A).sub.2M(IV)X.sub.6 are further described in Zhu et al. 2022 J Am Chem Soc 144:12450-12458 and Zhu et al. 2024 Science 383:86-93, the entire content of which references is incorporated by reference herein.

    [0135] Tables 1-17 below provide example details of the halide perovskite compounds having the formula (crown ether@A).sub.2M(IV)X.sub.6. Table 18 provides a non-exhaustive list of example compounds of the present disclosure.

    TABLE-US-00001 TABLE 1 Crystallographic tables for (18C6@K).sub.2TeCl.sub.6, (18C6@Rb).sub.2TeCl.sub.6, and (18C6@Cs).sub.2TeCl.sub.6, single crystals Crystal (18C6@K).sub.2TeCl.sub.6 (18C6@Rb).sub.2TeCl.sub.6 (18C6@Cs).sub.2TeCl.sub.6 ICSD Number 2122205 2122204 2122203 Empirical formula C.sub.24H.sub.48Cl.sub.6K.sub.2O.sub.12Te C.sub.24H.sub.48Cl.sub.6O.sub.12Rb.sub.2Te C.sub.24H.sub.48C.sub.16CS.sub.2O.sub.12Te Formula weight 947.12 1039.86 1134.74 Temperature/K. 293(2) 293(2) 293(2) Crystal system trigonal trigonal Trigonal Space group R-3 R-3 R-3 a/ 13.9266(6) 13.9737(6) 13.9417(3) b/ 13.9266(6) 13.9737(6) 13.9417(3) c/ 20.5594(8) 21.0360(9) 22.1002(6) / 90 90 90 / 90 90 90 y/ 120 120 120 Volume/.sup.3 3453.3(3) 3557.3(3) 3720.13(19) Z 3 3 3 pcalcmg/mm.sup.3 1.366 1.456 1.520 /mm.sup.1 1.218 3.046 2.410 F(000) 1440.0 1548.0 1656.0 Crystal size/mm.sup.3 0.51 0.388 0.194 0.185 0.155 0.136 0.273 0.174 0.082 Radiation Mo K ( = 0.71073) Mo K ( = 0.71073) Mo K ( = 0.71073) 2 range for data 5.85 to 58.914 7.77 to 58.946 5.844 to 52.744 collection Index ranges 15 h 16, 18 k 18 h 16,17 k 17 h 17, 17 k 15, 25 1 27 19, 26 1 27 17, 27 1 27 Reflections 8381 8997 22909 collected Independent 1857[R(int) = 0.0365] 1905[R(int) = 0.0329] 1697 [Rint = 0.0360, reflections Rsigma = 0.0120] Data/restraints/ 1857/0/69 1905/0/69 1697/0/69 parameters Goodness-of-fit on 1.043 1.100 1.063 F.sup.2 Final R indexes R.sub.1 = 0.0297, wR.sub.2 = R.sub.1 = 0.0450, wR.sub.2 = R.sub.1 = 0.0232, wR.sub.2 = [I>=20 (I)] 0.0774 0.1206 0.0655 Final R indexes R.sub.1 = 0.0361, wR.sub.2 = R.sub.1 = 0.0572, wR.sub.2 = R.sub.1 = 0.0291, wR.sub.2 = [all data] 0.0804 0.1272 0.0696 Largest diff. 1.01/-0.37 2.60/-0.85 0.66/-0.49 peak/hole / e .sup.3

    TABLE-US-00002 TABLE 2 Crystallographic tables for (18C6@K).sub.2TeBr.sub.6, (18C6@Rb).sub.2TeBr.sub.6, and (18C6@Cs).sub.2TeBr.sub.6, single crystals Crystal (18C6@K).sub.2TeBr.sub.6 (18C6@Rb).sub.2TeBr.sub.6 (18C6@Cs).sub.2TeBr.sub.6 ICSD Number 2122195 2122194 2122196 Empirical formula C.sub.24H.sub.48Br.sub.6K.sub.2O.sub.12Te C.sub.24H.sub.48Br.sub.6O.sub.12Rb.sub.2Te C.sub.24H.sub.48Br.sub.6O.sub.12Cs.sub.2Te Formula weight 1213.88 1306.62 369.44 Temperature/K. 293(2) 293(2) 293(2) Crystal system trigonal trigonal trigonal Space group R-3 R-3 R-3 a/ 14.2030(6) 14.2117(7) 14.1941(3) b/ 14.2030(6) 14.2117(7) 14.1941(3) c/ 21.3516(10) 21.6941(12) 22.5099(5) / 90 90 90 / 90 90 90 / 120 120 120 Volume/.sup.3 3730.1(4) 3794.6(4) 3927.53(19) Z 3 3 44 pcalcmg/mm.sup.3 1.621 1.715 6.873 /mm.sup.1 5.626 7.278 29.335 F(000) 1764.0 1872.0 6908.0 Crystal size/mm.sup.3 0.283 0.235 0.159 0.264 0.205 0.16 0.242 0.094 0.09 Radiation Mo K ( = 0.71073) Mo K ( = 0.71073) Mo K ( = 0.71073) 2 range for data 6.894 to 58.626 6.882 to 58.97 6.872 to 59.14 collection Index ranges 17 h 19, 17 h 18, 19 h 19, 18 k 18, 18 k 18, 19 k 19, 26 1 27 29 1 28 27 1 31 Reflections 9333 9547 29928 collected Independent 2005[R(int) = 0.0416] 2011[R(int) = 0.0377] 2260[R(int) = 0.0274] reflections Data/restraints/ 2005/0/69 2011/0/69 2260/0/69 parameters Goodness-of-fit 1.045 0.956 1.062 on F.sup.2 Final R indexes R.sub.1 = 0.0260, wR.sub.2 = R.sub.1 = 0.0184, wR.sub.2 = R.sub.1 = 0.0387, wR.sub.2 = [I >= 2 (I)] 0.0681 0.0425 0.1093 Final R indexes R.sub.1 = 0.0313, wR.sub.2 = R.sub.1 = 0.0241, wR.sub.2 = R.sub.1 = 0.0452, wR.sub.2 = [all data] 0.0693 0.0433 0.1135 Largest diff. 0.38/0.57 0.34/0.34 3.79/0.50 peak/hole/e .sup.3

    TABLE-US-00003 TABLE 3 Crystallographic tables for (18C6@K).sub.2SnCl.sub.6, (18C6@Rb).sub.2SnCl.sub.6, and (18C6@Cs).sub.2SnCl.sub.6, single crystals Crystal (18C6@K).sub.2SnCl.sub.6 (18C6@Rb).sub.2SnCl.sub.6 (18C6@Cs).sub.2SnCl.sub.6 ICSD Number 2122200 2122201 2122199 Empirical formula C.sub.24H.sub.48Cl.sub.6K.sub.2O.sub.12Sn C.sub.24H.sub.48Cl.sub.6O.sub.12Rb.sub.2Sn C.sub.24H.sub.48Cl.sub.6Cs.sub.2O.sub.12Sn Formula weight 938.21 1030.95 1125.83 Temperature/K. 293(2) 293(2) 293(2) Crystal system trigonal trigonal trigonal Space group R-3 R-3 R-3 a/ 13.9639(5) 13.9702(9) 13.9374(7) b/ 13.9639(5) 13.9702(9) 13.9374(7) c/ 20.2841(8) 20.8648(16) 22.0606(12) / 90 90 90 / 90 90 90 / 120 120 120 Volume/.sup.3 3425.3(3) 3526.5(5) 3711.2(4) Z 3 3 3 calcmg/mm.sup.3 1.364 1.456 1.511 /mm.sup.1 1.136 2.984 2.331 F(000) 1434.0 1542.0 1650.0 Crystal size/mm.sup.3 0.24 0.22 0.18 0.168 0.106 0.097 0.15 0.14 0.1 Radiation Mo K ( = 0.71073) Mo K ( = 0.71073) Mo K ( = 0.71073) 2 range for data 7.846 to 59.214 8.27 to 58.87 5.846 to 59.226 collection Index ranges 18 h 17, 17 k 16 h 18, 19 k 17 h 16, 18 k 18, 25 1 28 17, 26 1 26 18, 28 1 28 Reflections 8808 6255 9296 collected Independent 1822[R(int) = 0.0252] 1817[R(int) = 0.0324] 1998[R(int) = 0.0279] reflections Data/restraints/ 1822/0/69 1817/0/69 1998/0/69 parameters Goodness-of-fit on 1.159 1.028 1.228 F.sup.2 Final R indexes R.sub.1 = 0.0246, wR.sub.2 = R.sub.1 = 0.0269, wR.sub.2 = R.sub.1 = 0.0380, wR.sub.2 = [I >= 20 (I)] 0.0728 0.0599 0.1328 Final R indexes R.sub.1 = 0.0262, wR.sub.2 = R.sub.1 = 0.0381, wR.sub.2 = R.sub.1 = 0.0502, wR.sub.2 = [all data] 0.0736 0.0625 0.1480 Largest diff. 1.14/0.36 0.41/0.49 1.19/1.05 peak/hole/e .sup.3

    TABLE-US-00004 TABLE 4 Crystallographic tables for (18C6@K).sub.2SnBr.sub.6, (18C6@Rb).sub.2SnBr.sub.6, and (18C6@Cs).sub.2SnBr.sub.6, single crystals Crystal (18C6@K).sub.2SnBr.sub.6 (18C6@Rb).sub.2SnBr.sub.6 (18C6@Cs).sub.2SnBr.sub.6 ICSD Number 2122206 2122197 2122202 Empirical formula C.sub.24H.sub.48K.sub.6O.sub.12Sn C.sub.24H.sub.48Br.sub.6O.sub.12Rb.sub.2Sn C.sub.24H.sub.48Br.sub.6Cs.sub.2O.sub.12Sn Formula weight 1204.97 1297.71 1392.59 Temperature/K. 293(2) 293(2) 293(2) Crystal system trigonal trigonal triclinic Space group R-3 R-3 P-1 a/ 14.1856(7) 14.1962(8) 8.9775(2) b/ 14.1856(7) 14.1962(8) 9.0482(2) c/ 21.1321(12) 21.5006(11) 16.3064(4) / 90 90 95.516(2) / 90 90 90.129(2) / 120 120 104.150(2) Volume/.sup.3 3682.7(4) 3768.2(5) 1277.98(5) Z 3 3 1 calcmg/mm.sup.3 1.630 1.716 1.809 /mm.sup.1 5.613 7.245 6.633 F(000) 1758.0 1866.0 658.0 Crystal size/mm.sup.3 0.45 0.32 0.16 0.16 0.15 0.12 0.27 0.18 0.16 Radiation Mo K ( = 0.71073) Mo K ( = 0.71073) Mo K ( = 0.71073) 2 range for data 6.908 to 58.982 5.66 to 59.164 5.516 to 59.12 collection Index ranges 17 h 18, 17 k 18 h 16, 19 k 11 h 12, 12 k 18, 26 1 28 19, 29 1 27 12, 22 1 22 Reflections 9095 9515 28461 collected Independent 1973[R(int) = 0.0611] 2024[R(int) = 0.0313] 6089[R(int) = 0.0615] reflections Data/restraints/ 1973/0/70 2024/0/69 6089/0/205 parameters Goodness-of-fit on 1.098 1.068 1.031 F.sup.2 Final R indexes R.sub.1 = 0.0252, wR.sub.2 = R.sub.1 = 0.0255, wR.sub.2 = R.sub.1 = 0.0305, wR.sub.2 = [I >= 20 (I)] 0.0706 0.0682 0.0768 Final R indexes R.sub.1 = 0.0290, wR.sub.2 = R.sub.1 = 0.0305, wR.sub.2 = R.sub.1 = 0.0375, wR.sub.2 = [all data] 0.0715 0.0699 0.0788 Largest diff. 0.53/0.69 0.81/0.38 0.88/0.52 peak/hole/e .sup.3

    TABLE-US-00005 TABLE 5 Crystallographic tables for (18C6@K).sub.2PtCl.sub.6, (18C6@K).sub.2IrCl.sub.6 single crystals Crystal (18C6@K).sub.2PtCl.sub.6 (18C6@K).sub.2IrCl.sub.6 ICSD Number 2122198 2145199 Empirical formula C.sub.24H.sub.48Cl.sub.6K.sub.2O.sub.12Pt C.sub.24H.sub.48Cl.sub.6K.sub.2O.sub.12Ir Formula weight 1014.61 1011.72 Temperature/K. 293(2) 293(2) Crystal system trigonal trigonal Space group R-3 R-3 a/ 13.9074(6) 13.8805(2) b/ 13.9074(6) 13.8805 (2) c/ 20.0756(10) 20.2478(3) / 90 90 / 90 90 / 120 120 Volume/.sup.3 3362.7(3) 3378.46(11) Z 3 3 calcmg/mm.sup.3 1.503 1.492 /mm.sup.1 3.717 11.053 F(000) 1518.0 1515.0 Crystal size/mm.sup.3 0.125 0.09 0.085 0.13 0.07 0.03 Radiation Mo K ( = 0.71073) Cu K ( = 1.54184) 2 range for data 7.892 to 58.732 12.756 to 157.342 collection Index ranges 18 h 17, 17 h 17, 18 k 19, 17 k 17, 26 1 23 25 1 25 Reflections 6641 24775 collected Independent 1745[R(int) = 0.0268] 1615[R(int) = 0.0390] reflections Data/restraints/ 1745/0/69 1615/0/69 parameters Goodness-of-fit on 1.103 1.106 F.sup.2 Final R indexes R.sub.1 = 0.0341, R.sub.1 = 0.0145, [I >= 2 (I)] wR.sub.2 = 0.0818 wR.sub.2 = 0.0346 Final R indexes R1= 0.0355, R1=0.0147, [all data] wR2 = 0.0825 wR2 = 0.0347 Largest diff. 6.54/0.51 0.33/0.29 peak/hole/e .sup.3

    TABLE-US-00006 TABLE 6 Crystallographic tables for (18C6@K).sub.2SeCl.sub.6 and (18C6@Cs).sub.2ZeCl.sub.6 single crystals Crystal (18C6@K).sub.2SeCl.sub.6 (18C6@Cs).sub.2ZrCl.sub.6 ICSD Number 2145198 2145197 Empirical formula C.sub.24H.sub.48Cl.sub.6K.sub.2O.sub.12Se C.sub.24H.sub.48C.sub.16Cs.sub.2O.sub.12Zr Formula weight 898.48 1098.36 Temperature/K. 293(2) 293(2) Crystal system trigonal trigonal Space group R-3 R-3 a/ 13.8912(4) 13.8547(2) b/ 13.8912(4) 13.8547(2) c/ 20.3021(6) 21.9616(4) / 90 90 / 90 90 / 120 120 Volume/.sup.3 3392.7(2) 3650.81(12) Z 3 3 pcalcmg/mm.sup.3 1.319 1.499 /mm.sup.1 1.412 16.729 F(000) 1386.0 1620.0 Crystal size/mm.sup.3 0.267 0.18 0.142 0.07 0.07 0.05 Radiation Mo K ( = 0.71073) Cu K ( = 1.54184) 2 range for data 6.02 to 59.246 8.398 to 157.208 collection Index ranges 17 h 18, 17 h 17, 18 k 18, 17 k 17, 27 l 27 27 l 24 Reflections collected 27084 26784 Independent 1959[R(int) = 0.0434] 1750[R(int) = 0.0194] reflections Data/restraints/ 1959/0/69 1750/0/69 parameters Goodness-of-fit on F.sup.2 1.077 1.075 Final R indexes R.sub.1 = 0.0477, R.sub.1 = 0.0282, [ I >= 2 (I)] wR.sub.2 = 0.1443 wR.sub.2 = 0.0776 Final R indexes R.sub.1 = 0.0502, R.sub.1 = 0.0297, [all data] wR.sub.2 = 0.1457 wR.sub.2 = 0.0787 Largest diff. peak/ 2.67/0.43 0.68/0.49 hole/e .sup.3

    TABLE-US-00007 TABLE 7 Crystallographic tables for (18C6@Cs)2TeI6 single crystals Crystal (18C6@Cs).sub.2TeI.sub.6 ICSD Number 2122192 Empirical formula C.sub.27Cs.sub.2I.sub.6NO.sub.13Te Formula weight 1701.10 Temperature/K. 293(2) Crystal system monoclinic Space group P21/m a/ 9.8064(2) b/ 14.6116(4) c/ 17.8497(4) / 90 / 93.572(2) / 90 Volume/.sup.3 2552.66(10) Z 2 pcalcmg/mm.sup.3 2.213 /mm.sup.1 5.661 F(000) 1506.0 Crystal size/mm.sup.3 0.493 0.339 0.199 Radiation Mo K ( = 0.71073) 2 range for data 6.374 to 58.762 collection Index ranges 12 h 13, 19 k 18, 22 l 24 Reflections collected 37382 Independent reflections 6491 [Rint = 0.1203, Rsigma = 0.0514] Data/restraints/parameters 6491/0/248 Goodness-of-fit on F.sup.2 1.098 Final R indexes R.sub.1 = 0.0661, [ I >= 2 (I)] wR.sub.2 = 0.1956 Final R indexes R.sub.1 = 0.0726, [all data] wR.sub.2 = 0.2010 Largest diff. peak/ 1.48/2.18 hole/e .sup.3

    TABLE-US-00008 TABLE 8 Crystallographic tables for (18C6@K).sub.2TeBr.sub.6 synthesized with ACN or DMF Crystal (18C6@K).sub.2TeBr.sub.6-DMF (18C6@K).sub.2TeBr.sub.6-ACN ICSD Number 2122195 2122193 Empirical formula C.sub.24H.sub.48Br.sub.6K.sub.2O.sub.12Te C.sub.24H.sub.48Br.sub.6K.sub.2O.sub.12Te Formula weight 1213.88 1213.88 Temperature/K. 293(2) 293(2) Crystal system trigonal trigonal Space group R-3 R-3 a/ 14.2030(6) 14.1660(6) b/ 14.2030(6) 14.1660(6) c/ 21.3516(10) 21.1805(11) / 90 90 / 90 90 / 120 120 Volume/.sup.3 3730.1(4) 3681.0(4) Z 3 3 pcalcmg/mm.sup.3 1.621 1.643 /mm.sup.1 5.626 5.701 F(000) 1764.0 1764.0 Crystal size/mm.sup.3 0.283 0.235 0.159 0.28 0.26 0.09 Radiation Mo K ( = 0.71073) Mo Ka ( = 0.71073) 2 range for data 6.894 to 58.626 7.678 to 59.044 collection Index ranges 17 h 19, 19 h 18, 18 k 18, 19 k 16, 26 l 27 27 l 24 Reflections collected 9333 9351 Independent reflections 2005[R(int) = 0.0416] 1950[R(int) = 0.0243] Data/restraints/parameters 2005/0/69 1950/0/70 Goodness-of-fit on F.sup.2 1.045 1.073 Final R indexes R.sub.1 = 0.0260, R.sub.1 = 0.0172, [ I >= 2 (I)] wR.sub.2 = 0.0681 wR.sub.2 = 0.0412 Final R indexes R.sub.1 = 0.0313, R.sub.1 = 0.0210, [all data] wR.sub.2 = 0.0693 wR.sub.2 = 0.0418 Largest diff. 0.38/0.57 0.22/0.41 peak/hole/e .sup.3

    TABLE-US-00009 TABLE 9 Crystallographic tables for (21C7@Cs).sub.2TeBr.sub.6, and (21C7@Cs).sub.2TeI.sub.6 single crystals Crystal (21C7@Cs).sub.2TeBr.sub.6 (21C7@Cs).sub.2TeI.sub.6 ICSD Number 2122191 2122190 Empirical formula C.sub.31H.sub.43Br.sub.6Cs.sub.2NO.sub.15Te C.sub.30H.sub.35Cs.sub.2I.sub.6NO.sub.15Te Formula weight 1542.54 1803.40 Temperature/K. 293(2) 293(2) Crystal system orthorhombic orthorhombic Space group Cmc21 Cmc21 a/ 15.6291(6) 15.7635(11) b/ 12.0777(4) 12.3817(10) c/ 27.5528(18) 28.124(3) / 90 90 / 90 90 / 90 90 Volume/.sup.3 5201.0(4) 5489.1(8) Z 4 4 pcalcmg/mm.sup.3 1.970 2.182 /mm.sup.1 21.138 5.274 F(000) 2912.0 3284.0 Crystal size/mm.sup.3 0.091 0.051 0.05 0.157 x 0.103 0.045 Radiation Cu K ( = 1.54184) Mo K ( = 0.71073) 2 range for data 9.796 to 158.18 5.926 to 52.74 collection Index ranges 19 h 19, 19 h 17, 11 k 15, 14 k 15, 34 l 34 35 l 35 Reflections collected 53691 19078 Independent 5669 [Rint = 0.1006, 5213 [Rint = 0.0863, reflections Rsigma = 0.0378] Rsigma = 0.0757] Data/restraints/ 5669/1/220 5213/1/169 parameters Goodness-of-fit on F.sup.2 1.048 1.016 Final R indexes R.sub.1 = 0.0497, R.sub.1 = 0.0505, [ I >= 2 (I)] wR.sub.2 = 0.1233 wR.sub.2 = 0.0955 Final R indexes R.sub.1 = 0.0668, R.sub.1 = 0.0873, [all data] wR.sub.2 = 0.1320 wR.sub.2 = 0.1060 Largest diff. 0.56/0.81 0.63/0.83 peak/hole/e .sup.3

    TABLE-US-00010 TABLE 10 Crystallographic tables for (18C6@K).sub.2HfBr.sub.6 and (18C6@K).sub.2ZrBr.sub.6 Crystal (18C6@K).sub.2HfBr.sub.6 (18C6@K).sub.2ZrBr.sub.6 ICSD Number 2225998 2225999 Empirical formula C.sub.24H.sub.48Br.sub.6K.sub.2O.sub.12Hf C.sub.24H.sub.48Br.sub.6K.sub.2O.sub.12Zr Formula weight 1264.77 1177.50 Temperature/K. 293(2) 293(2) Crystal system trigonal trigonal Space group R-3 R-3 a/ 14.13320(10) 14.13940(10) b/ 14.13320(10) 14.13940(10) c/ 21.0819(2) 21.0727(2) / 90 90 / 90 90 / 120 120 Volume/.sup.3 3635.98(6) 3648.49(6) Z 3 3 pcalcmg/mm.sup.3 1.733 1.608 /mm.sup.1 11.670 9.517 F(000) 1824.0 1728.0 Crystal size/mm.sup.3 0.15 0.12 0.108 0.09 0.07 0.06 Radiation Cu K ( = 1.54184 ) Cu K ( = 1.54184 A) 2 range for data 12.526 to 157.206 8.325 to 157.42 collection Index ranges 17 h 17, 17 h 17, 17 k 17, 17 k 17, 24 l 26 25 l 26 Reflections 26285 26501 collected Independent 1737[R(int) = 0.0268] 1753[R(int) = 0.0387] reflections Data/restraints/ 1737/0/70 1753/0/70 parameters Goodness-of-fit 1.103 1.106 on F.sup.2 Final R indexes R.sub.1 = 0.0171, R.sub.1 = 0.0183, [ I >= 2 (I)] wR.sub.2 = 0.0496 wR.sub.2 = 0.0500 Final R indexes R.sub.1 = 0.0171 R.sub.1 = 0.0183, [all data] wR.sub.2 = 0.0496 wR.sub.2 = 0.0503 Largest diff. 0.34/0.43 0.48/0.26 peak/hole/e .sup.3

    TABLE-US-00011 TABLE 11 A summary of the PLQY determination results of two different batches and three measurements per batch of the (18C6@K).sub.2HfBr.sub.6 powders Measurement 1 Measurement 2 Measurement 3 Average Batch 1 97.31% 97.57% 100.67% 98.52% Batch 2 93.46% 94.89% 93.38% 93.91%

    TABLE-US-00012 TABLE 12 Crystallographic tables for (18C6@K).sub.2ZrCl.sub.4Br.sub.2 Crystal (18C6@K).sub.2ZrCl.sub.4Br.sub.2 ICSD Number 2292758 Empirical formula C.sub.24H.sub.48Cl.sub.4.3Br.sub.1.7K.sub.2O.sub.12Zr Formula weight 986.47 Temperature/K. 293(2) Crystal system trigonal Space group R-3 a/ 14.0091(6) b/ 14.0091(6) c/ 20.6138(11) / 90 / 90 / 120 Volume/.sup.3 3503.6(4) Z 3 pcalcmg/mm.sup.3 1.403 /mm.sup.1 2.159 F(000) 1496.0 Crystal size/mm.sup.3 0.08 0.06 0.04 Radiation Mo K ( = 0.71073 ) 2 range for data 7.002 to 59.562 collection Index ranges 17 h 18, 18 k 17, 27 l 22 Reflections collected 9250 Independent reflections 1973[R(int) = 0.0168] Data/restraints/parameters 1973/0/70 Goodness-of-fit on F.sup.2 1.086 Final R indexes R.sub.1 = 0.0302, [ I >= 2 (I)] wR.sub.2 = 0.1163 Final R indexes R.sub.1 = 0.0334, [all data] wR.sub.2 = 0.1180 Largest diff. 1.71/0.39 peak/hole/e .sup.3

    TABLE-US-00013 TABLE 13 A summary of the PLQY determination results of two different batches and three measurements per batch of the (18C6@K).sub.2ZrCLBr.sub.2 powders Measurement 1 Measurement 2 Average Batch 1 80.29% 82.76% 81.53% Batch 2 84.92% 82.77% 83.85%

    TABLE-US-00014 TABLE 14 IC-AES concentrations of Hf and Zr in HfBr4 precursor and (18C6@K)zHfBr.sub.6 single crystals ICP-AES Concentration (ppm) Sample Atomic Percent Composition Hf Zr of Zr HfBr4 92.89 3.36 0.226 0.016 0.474% (18C6@K).sub.2HfBr.sub.6 124.9 4.69 0.405 0.008 0.630%

    TABLE-US-00015 TABLE 15 FWHM of the PL spectra of (18C6@K).sub.2HfBr.sub.6 powders from 4 K. to 293 K. Temperature (K.) FWHM (meV) 4 482.4 6 481.8 8 482.2 10 494.2 12 496.9 15 485.9 20 476.2 25 480.5 30 474.9 35 484.3 40 488.9 45 490.2 50 483.0 60 492.0 70 499.5 80 513.5 90 526.0 100 538.3 110 554.6 120 560.1 130 571.4 140 580.7 150 588.8 170 602.7 190 623.1 210 630.7 230 632.3 250 643.9 270 654.9 293 666.6

    TABLE-US-00016 TABLE 16 Parameters of the single-exponential decay fit of the PL decay of a (18C6@K).sub.2ZrBr.sub.6 single crystal Model ExpDec1 Equation y = A.sub.1 e.sup.(x/t1) + y.sub.0 Plot (18C6@K)2ZrBr6 y.sub.0 4.49168 10.sup.5 2.15919 10.sup.5 A.sub.1 0.0313 6.16847 10.sup.5 t.sub.1 6.79835 0.0262 Reduced Chi-Sqr 6.36744 10.sup.7 R-Square (COD) 0.98853 Adj. R-Square 0.98853

    TABLE-US-00017 TABLE 17 Parameters of the single-exponential decay fit of the PL decay of a (18C6@K).sub.2ZrCl.sub.4Br.sub.2 le crystal Model ExpDec1 Equation y = A.sub.1 e.sup.(x/t1) + y.sub.0 Plot (18C6@K).sub.2ZrCl.sub.4Br.sub.2 y.sub.0 0.00492 5.2498 10.sup.5 A.sub.1 0.05606 6.35752 10.sup.5 t.sub.1 12.08304 0.04017 Reduced Chi-Sqr 1.0178 10.sup.6 R-Square (COD) 0.99496 Adj. R-Square 0.99495

    TABLE-US-00018 TABLE 18 List of examples of (crown ether@A).sub.2M(IV)X.sub.6 crown ether@A 18C6Cs 18C6Rb 18C6K 21C7Cs 21C7Rb 21C7K M(IV)X.sub.6 TeCl.sub.6 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 TeCl.sub.6 TeCl.sub.6 TeCl.sub.6 TeCl.sub.6 TeCl.sub.6 TeCl.sub.6 TeBr.sub.6 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 TeBr.sub.6 TeBr.sub.6 TeBr.sub.6 TeBr.sub.6 TeBr.sub.6 TeBr.sub.6 TeI.sub.6 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 TeI.sub.6 TeI.sub.6 TeI.sub.6 TeI.sub.6 TeI.sub.6 TeI.sub.6 SnCl.sub.6 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 SnCl.sub.6 SnCl.sub.6 SnCl.sub.6 SnCl.sub.6 SnCl.sub.6 SnCl.sub.6 SnBr.sub.6 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 SnBr.sub.6 SnBr.sub.6 SnBr.sub.6 SnBr.sub.6 SnBr.sub.6 SnBr.sub.6 SnI.sub.6 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 SnI.sub.6 SnI.sub.6 SnI.sub.6 SnI.sub.6 SnI.sub.6 SnI.sub.6 PtCl.sub.6 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 PtCl.sub.6 PtCl.sub.6 PtCl.sub.6 PtCl.sub.6 PtCl.sub.6 PtCl.sub.6 PtBr.sub.6 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 PtBr.sub.6 PtBr.sub.6 PtBr.sub.6 PtBr.sub.6 PtBr.sub.6 PtBr.sub.6 PtI.sub.6 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 PtI.sub.6 PtI.sub.6 PtI.sub.6 PtI.sub.6 PtI.sub.6 PtI.sub.6 SeCl.sub.6 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 SeCl.sub.6 SeCl.sub.6 SeCl.sub.6 SeCl.sub.6 SeCl.sub.6 SeCl.sub.6 SeBr.sub.6 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 SeBr.sub.6 SeBr.sub.6 SeBr.sub.6 SeBr.sub.6 SeBr.sub.6 SeBr.sub.6 SeI.sub.6 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 SeI.sub.6 SeI.sub.6 SeI.sub.6 SeI.sub.6 SeI.sub.6 SeI.sub.6 IrCl.sub.6 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 IrCl.sub.6 IrCl.sub.6 IrCl.sub.6 IrCl.sub.6 IrCl.sub.6 IrCl.sub.6 IrBr.sub.6 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 IrBr.sub.6 IrBr.sub.6 IrBr.sub.6 IrBr.sub.6 IrBr.sub.6 IrBr.sub.6 IrI.sub.6 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 IrI.sub.6 IrI.sub.6 IrI.sub.6 IrI.sub.6 IrI.sub.6 IrI.sub.6 ZrCl.sub.6 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 ZrCl.sub.6 ZrCl.sub.6 ZrCl.sub.6 ZrCl.sub.6 ZrCl.sub.6 ZrCl.sub.6 ZrBr.sub.6 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 ZrBr.sub.6 ZrBr.sub.6 ZrBr.sub.6 ZrBr.sub.6 ZrBr.sub.6 ZrBr.sub.6 ZrI.sub.6 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 ZrI.sub.6 ZrI.sub.6 ZrI.sub.6 ZrI.sub.6 ZrI.sub.6 ZrI.sub.6 HfCl.sub.6 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 HfCl.sub.6 HfCl.sub.6 HfCl.sub.6 HfCl.sub.6 HfCl.sub.6 HfCl.sub.6 HfBr.sub.6 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 HfBr.sub.6 HfBr.sub.6 HfBr.sub.6 HfBr.sub.6 HfBr.sub.6 HfBr.sub.6 HfI.sub.6 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 HfI.sub.6 HfI.sub.6 HfI.sub.6 HfI.sub.6 HfI.sub.6 HfI.sub.6 CeCl.sub.6 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 CeCl.sub.6 CeCl.sub.6 CeCl.sub.6 CeCl.sub.6 CeCl.sub.6 CeCl.sub.6 CeBr.sub.6 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 CeBr.sub.6 CeBr.sub.6 CeBr.sub.6 CeBr.sub.6 CeBr.sub.6 CeBr.sub.6 CeI.sub.6 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 CeI.sub.6 CeI.sub.6 CeI.sub.6 CeI.sub.6 CeI.sub.6 CeI.sub.6 Cl.sub.5Br (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 Cl.sub.5Br Cl.sub.5Br Cl.sub.5Br Cl.sub.5Br Cl.sub.5Br Cl.sub.5Br Cl.sub.4Br.sub.2 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 Cl.sub.4Br.sub.2 Cl.sub.4Br.sub.2 Cl.sub.4Br.sub.2 Cl.sub.4Br.sub.2 Cl.sub.4Br.sub.2 Cl.sub.4Br.sub.2 Cl.sub.3Br.sub.3 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 Cl.sub.3Br.sub.3 Cl.sub.3Br.sub.3 Cl.sub.3Br.sub.3 Cl.sub.3Br.sub.3 Cl.sub.3Br.sub.3 Cl.sub.3Br.sub.3 Cl.sub.2Br.sub.4 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 Cl.sub.2Br.sub.4 Cl.sub.2Br.sub.4 Cl.sub.2Br.sub.4 Cl.sub.2Br.sub.4 Cl.sub.2Br.sub.4 Cl.sub.2Br.sub.4 ClBr.sub.5 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 ClBr.sub.5 ClBr.sub.5 ClBr.sub.5 ClBr.sub.5 ClBr.sub.5 ClBr.sub.5 Cl.sub.5I (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 Cl.sub.5I Cl.sub.5I Cl.sub.5I Cl.sub.5I Cl.sub.5I Cl.sub.5I Cl.sub.4I.sub.2 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 Cl.sub.4I.sub.2 Cl.sub.4I.sub.2 Cl.sub.4I.sub.2 Cl.sub.4I.sub.2 Cl.sub.4I.sub.2 Cl.sub.4I.sub.2 Cl.sub.3I.sub.3 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 Cl.sub.3I.sub.3 Cl.sub.3I.sub.3 Cl.sub.3I.sub.3 Cl.sub.3I.sub.3 Cl.sub.3I.sub.3 Cl.sub.3I.sub.3 Cl.sub.2I.sub.4 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 Cl.sub.2I.sub.4 Cl.sub.2I.sub.4 Cl.sub.2I.sub.4 Cl.sub.2I.sub.4 Cl.sub.2I.sub.4 Cl.sub.2I.sub.4 ClI.sub.5 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 ClI.sub.5 ClI.sub.5 ClI.sub.5 ClI.sub.5 ClI.sub.5 ClI.sub.5 Br.sub.5I (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 Br.sub.5I Br.sub.5I Br.sub.5I Br.sub.5I Br.sub.5I Br.sub.5I Br.sub.4I.sub.2 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 Br.sub.4I.sub.2 Br.sub.4I.sub.2 Br.sub.4I.sub.2 Br.sub.4I.sub.2 Br.sub.4I.sub.2 Br.sub.4I.sub.2 Br.sub.3I.sub.3 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 Br.sub.3I.sub.3 Br.sub.3I.sub.3 Br.sub.3I.sub.3 Br.sub.3I.sub.3 Br.sub.3I.sub.3 Br.sub.3I.sub.3 Br.sub.2I.sub.4 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 Br.sub.2I.sub.4 Br.sub.2I.sub.4 Br.sub.2I.sub.4 Br.sub.2I.sub.4 Br.sub.2I.sub.4 Br.sub.2I.sub.4 BrI.sub.5 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 BrI.sub.5 BrI.sub.5 BrI.sub.5 BrI.sub.5 BrI.sub.5 BrI.sub.5 Cl.sub.4BrI (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 Cl.sub.4BrI Cl.sub.4BrI Cl.sub.4BrI Cl.sub.4BrI Cl.sub.4BrI Cl.sub.4BrI Cl.sub.3Br.sub.2I (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 Cl.sub.3Br.sub.2I Cl.sub.3Br.sub.2I Cl.sub.3Br.sub.2I Cl.sub.3Br.sub.2I Cl.sub.3Br.sub.2I Cl.sub.3Br.sub.2I Cl.sub.3BrI.sub.2 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 Cl.sub.3BrI.sub.2 Cl.sub.3BrI.sub.2 Cl.sub.3BrI.sub.2 Cl.sub.3BrI.sub.2 Cl.sub.3BrI.sub.2 Cl.sub.3BrI.sub.2 Cl.sub.2Br.sub.3I (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 Cl.sub.2Br.sub.3I Cl.sub.2Br.sub.3I Cl.sub.2Br.sub.3I Cl.sub.2Br.sub.3I Cl.sub.2Br.sub.3I Cl.sub.2Br.sub.3I Cl.sub.2Br.sub.2I.sub.2 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 Cl.sub.2Br.sub.2I.sub.2 Cl.sub.2Br.sub.2I.sub.2 Cl.sub.2Br.sub.2I.sub.2 Cl.sub.2Br.sub.2I.sub.2 Cl.sub.2Br.sub.2I.sub.2 Cl.sub.2Br.sub.2I.sub.2 Cl.sub.2BrI.sub.3 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 Cl.sub.2BrI.sub.3 Cl.sub.2BrI.sub.3 Cl.sub.2BrI.sub.3 Cl.sub.2BrI.sub.3 Cl.sub.2BrI.sub.3 Cl.sub.2BrI.sub.3 ClBr.sub.4I (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 ClBr.sub.4I ClBr.sub.4I ClBr.sub.4I ClBr.sub.4I ClBr.sub.4I ClBr.sub.4I ClBr.sub.3I.sub.2 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 ClBr.sub.3I.sub.2 ClBr.sub.3I.sub.2 ClBr.sub.3I.sub.2 ClBr.sub.3I.sub.2 ClBr.sub.3I.sub.2 ClBr.sub.3I.sub.2 ClBr.sub.2I.sub.3 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 ClBr.sub.2I.sub.3 ClBr.sub.2I.sub.3 ClBr.sub.2I.sub.3 ClBr.sub.2I.sub.3 ClBr.sub.2I.sub.3 ClBr.sub.2I.sub.3 ClBrI.sub.4 (18C6Cs).sub.2 (18C6Rb).sub.2 (18C6K).sub.2 (21C7Cs).sub.2 (21C7Rb).sub.2 (21C7K).sub.2 ClBrI.sub.4 ClBrI.sub.4 ClBrI.sub.4 ClBrI.sub.4 ClBrI.sub.4 ClBrI.sub.4
    (ii) Halide Perovskite Compound (Crown Ether@A)M(II)X.sub.4 or (Crown Ether@A)M(III)X.sub.5

    [0136] A halide perovskite compound according to the formula: (crown ether@A)M(II)X.sub.4 has the M, at least one divalent metal cation; the X, at least one halide anion; and the crown ether@A, at least one alkali metal-bound crown ether formed between an alkali metal cation A and oxygen atoms of a crown ether, e.g., by electrostatic interaction. The (crown ether@A)M(II)X.sub.4 can form a tetrahedral unit. A halide perovskite compound according to the formula: (crown ether@A)M(III)X.sub.5 has the M, at least one divalent metal cation; the X, at least one halide anion; and the crown ether@A, at least one alkali metal-bound crown ether formed between an alkali metal cation A and oxygen atoms of a crown ether, e.g., by electrostatic interaction. The (crown ether@A)M(III)X.sub.5 can form an octahedral unit.

    [0137] The halide perovskite compound provided herein can be tunable by adjusting components, i.e., crown ether, A, M(II), M(III), and X. For example, the M(II) can be one or more of Mn.sup.2+ and Ni.sup.2+; the M(III) can be Sb3+; the X can be one or more of Cl and Br; the crown ether can be 18-Crown-6 (18C6); and/or the A can be Ba2.sup.+. For example, X4 can be any combination of Cl and Br, such as Cl4, Cl3Br, Cl2Br2, ClBr3, and Br4. For example, X.sub.5 can be any combination of Cl.sup. and Br.sup., such as Cl.sub.5, Cl.sub.4Br, Cl.sub.3Br.sub.2, Cl.sub.2Br.sub.3, ClBr.sub.4, and Br.sub.4. In specific embodiments, the halide perovskite compound is (18C6@Ba)MnBr.sub.4 or (18C6@Ba)SbCl.sub.5.

    [0138] The metal halide [M(II)X.sub.4].sup.2 or [M(III)X.sub.5].sup.2 can form a 1D linear chain structure with the crown ether@A.sup.2+. The halide perovskite compound can comprise a structural unit formed by one crown ether@A.sup.2+ and one [M(II)X.sub.4].sup.2, a linear chain structure comprising a plurality of the structural unit, and/or a hexagonal crystal structure comprising the plurality of the structural unit. For example, in the crystal structure, the [M(II)X.sub.4].sup.2 complexes and the (crown ether@A).sup.+ complexes can be alternatingly connected into a linear chain, and the chains then packed into a hexagonal crystal structure. One side of the A.sup.2+ atom can be coordinated with one X.sup. atom, and the other side can be coordinated with three A.sup.2+ atoms (FIGS. 74A-74D). This configuration enables the strong structural stability of the [M(II)X.sub.4].sup.2 complexes, and can generate the near perfect tetrahedral shape of the [M(II)X.sub.4].sup.2 complexes. This has great implications on the emission color of the [M(II)X.sub.4].sup.2 complexes.

    [0139] Similarly, the halide perovskite compound can comprise at least one of (i) a structural unit formed by one (crown ether@A).sup.2+ and one [M(III)X.sub.5].sup.2, (ii) a linear chain structure comprising a plurality of the structural unit, and (iii) a hexagonal or rhombohedral crystal structure comprising the plurality of the structural unit. For example, upon crystallization, [M(III)X.sub.5].sup.2 complexes can be assembled into a linear chain structure facilitated by (crown ether@A).sup.2+ (FIGS. 76A, 76B). The A.sup.2+ in the crown ether can be disordered. Half of the cation can be located above the crown ether, while the other half below the crown ether, and the crown ether can be the mirror plane for the two parts. The [M(III)X.sub.5].sup.2 complexes can be also disordered, and the 5 X.sup. atoms can occupy 6 octahedral coordination sites of the M(III) atom, each with 5/6 possibility. The alternating linear chains can be then assembled into a rhombohedral crystal structure with R-3 space group. This high symmetry space group guarantees the linearity of the 1D chains (FIGS. 76C, 76D, Table 21).

    [0140] The halide perovskite compound (crown ether@A)M(II)X.sub.4 or (crown ether@A)M(III)X.sub.5 can be in any form such as in powder, crystal, or solution. The halide perovskite compound (crown ether@A)M(II)X.sub.4 or (crown ether@A)M(III)X.sub.5 can have higher purity as compared to a control compound (e.g., AM(II)X.sub.4 without the crown ether and comprising the same A, M(II), and X as the halide perovskite compound (crown ether@A)M(II)X.sub.4), or AM(III)X.sub.5 without the crown ether and comprising the same A, M(III), and X as the halide perovskite compound (crown ether@A)M(III)X.sub.5). The purity of the halide perovskite compound (crown ether@A)M(II)X.sub.4 can be about 80%, 81%, 82%, 83%, 84%, 85%, 96%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 99.5%, or greater.

    [0141] The halide perovskite compound can comprise greater PLQY as compared to a control compound A.sub.2M(II)X.sub.4 or AM(III)X.sub.5 without the crown ether and comprising the same A, M(II) or M(III), and X as the halide perovskite compound. For example, the PLQY of the halide perovskite compound can be about 80%, 81%, 82%, 83%, 84%, 85%, 96%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or greater. The PLQY can be measured at various excitation/emission wavelength, including under excitation by blue light (e.g., from about 425 nm to about 475 nm) (e.g., at 449 nm), measured at about 495-570 nm (e.g., 513 nm) (green light emission), For example, formula (18C6@Ba)MnBr.sub.4 has the PLQY value of 82.1% and narrow emission peak (full width at half maximum (FWHM)=0.17 eV) under excitation at 449 nm and measured at 513 nm. Formula (18C6@Ba)SbCl.sub.5 has a uniform orange emission under 375-nm excitation.

    [0142] The halide perovskite compound provided herein can have increased air stability as compared to a control compound AM(II)X.sub.4 or AM(III)X.sub.5 without the crown ether and comprising the same A, M, and X as the halide perovskite compound. In some embodiments, the air stability of the halide perovskite compound is increased by about 1 hour to about 3 days as compared to the control compound.

    [0143] Table 19 provides a non-exhaustive list of example compounds of the present disclosure.

    TABLE-US-00019 TABLE 19 List of examples of (crown ether@A)M(II)X.sub.4 or (crown ether@A)M(III)X.sub.5 thar forms a linear chain structure M Mn.sup.2+ Ni.sup.2+ Sb.sup.3+ X.sub.4 Cl.sub.4 (18C6Ba)MnCl.sub.4 (18C6Ba)NiCl.sub.4 Br.sub.4 (18C6Ba)MnBr.sub.4 (18C6Ba)NiBr.sub.4 Cl.sub.3Br (18C6Ba)MnCl.sub.3Br (18C6Ba)NiCl.sub.3Br Cl.sub.2Br.sub.2 (18C6Ba)MnCl.sub.2Br.sub.2 (18C6Ba)NiCl.sub.2Br.sub.2 ClBr.sub.3 (18C6Ba)MnClBr3 (18C6Ba)NiClBr.sub.3 X.sub.5 Cl.sub.5 (18C6Ba)Cl.sub.5 Br.sub.5 (18C6Ba)Br.sub.5 Cl.sub.4Br (18C6Ba)Cl.sub.4Br Cl.sub.3Br.sub.2 (18C6Ba)Cl.sub.3Br.sub.2 Cl.sub.2Br.sub.3 (18C6Ba)Cl.sub.2Br.sub.3 ClBr.sub.4 (18C6Ba)ClBr.sub.4

    B. Generating Halide Perovskite Compound Using Supramolecule Assembly

    [0144] Methods of generating a halide perovskite compound provided herein include dissolving (i) a metal halide and (ii) an alkali metal halide and a crown ether, or an alkali metal-bound crown ether, in an organic solvent to provide a precursor solution, to contact the metal halide with at least one of the alkali metal halide, the crown ether, and the alkali metal-bound crown ether in the precursor solution; and contacting the organic solvent with an anti-solvent, to crystalize the halide perovskite compound from the precursor solution. The organic solvent can include N, N-Dimethylformamide (DMF) or acetonitrile (ACN). The anti-solvent can include diethyl ether (DEE). The fabrication reaction, i.e., dissolving (i) the metal halide and (ii) the alkali metal and the crown ether, or the alkali metal-bound crown ether in the organic solvent can be conducted at about 60-100 C., such as at about 80 C.

    [0145] For example, to generate (18C6@A).sub.2M(IV)X.sub.6 (A=Cs.sup.+, Rb.sup.+, K.sup.+; M(IV)=Te.sup.4+, Sn.sup.4+, Se.sup.4+, Ir.sup.4+, Pt.sup.4+, Zr.sup.4+, Ce.sup.4+; X=Cl.sup., Br.sup., I.sup.), Powders of A.sub.2MX.sub.6 and 18C6 are measured into a 20 ml vial based on the 1:2 stoichiometric ratio, and the precursors are dissolved in 10 ml ACN or DMF on a hot plate at 100 C. with vigorous stirring for three hours. The supersaturated solution is filtered into a new 20 ml vial. (18C6@A).sub.2M(IV)X.sub.6 powders are obtained by adding 10 ml of the supersaturated solution into 20 ml of DEE anti-solvent. The mixtures are centrifuged at 4000 rpm for 5 minutes to separate the powders and the solution. The powders are dried in a vacuum oven at 50 C. overnight. (18C6@A).sub.2M(IV)X.sub.6 single crystals are grown using an anti-solvent diffusion method. Briefly, 1 ml of the above mentioned supersaturated solution is added into a 4 ml vial, which is placed into a 20 ml vial with 4 ml of DEE. After approximately two days, single crystals are formed on the bottom and the wall of the 4 ml vial. Single crystals are washed 3 times with acetone and stored in an argon glovebox for future use.

    [0146] For example, to generate (18C6@Ba)M(II)X.sub.4 (M(II)=Mn.sup.2+, Ni.sup.2+; X=Cl.sup., Br.sup.), a clear precursor solution can be obtained with ACN at 80 C. with the concentration of 10 mM for 18C6, BaX.sub.2 and M(II)X.sub.2. (18C6@Ba)M(II)X.sub.4 powders and single crystals were grown using the similar diethyl ether-assisted anti-solvent crystallization method as described above.

    [0147] For example, to generate (18C6@Ba)M(III)X.sub.5 (M(III)=Sb.sup.3+; X=Cl.sup., Br.sup.), ACN can be applied as the solvent to dissolve a stoichiometric ratio amount of 18C6, BaX.sub.2, and M(III)X.sub.3 precursors, and DEE can be used as the anti-solvent, using the similar methods as described above.

    [0148] In some the halide perovskite compound generated according to the method provided herein is free of impurities. Free of impurities as used herein refers to the compound or composition containing no impurities, or insignificant or negligible amount of impurities. For example, a compound that is free of impurities can have purity of about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.6%, 99.7%, 99.8%, 99.9%, or greater.

    [0149] The methods provided herein can be more cost effective and facile as compared to other methods to synthesize or stabilize metal halide perovskite. In the methods provided herein, all the compositions can be fabricated using polar organic solvents at about 80 C. The methods provided herein are solution processable and easy to scale up. In contrast, in methods of generating vacancy-ordered perovskites (e.g., A.sub.2M(IV)X.sub.6, AM(II)X.sub.4, AM(III)X.sub.5) some double perovskites, such as Cs2ZrBr6 and Cs2HfBr6, require high temperature (e.g., about 800 C.) solid-state synthesis.

    [0150] Further, the methods provided herein can achieve 100% pure solids, including both single crystals and powders. The purity of the synthetic product is much higher than the vacancy-ordered perovskites. For example, (18-Crown-6@K).sub.2ZrBr.sub.6, (18-Crown-6@K).sub.2HfBr.sub.6, and (18-Crown-6@Ba)MnBr.sub.4 are pure according to powder XRD measurements, whereas the synthesis of Cs.sub.2ZrBr.sub.6, Cs.sub.2HfBr.sub.6, or BaMnBr.sub.4 can result in non-negligible CsBr or BaBr.sub.2 impurities.

    [0151] The methods provided herein can provide improved stability of the metal halide perovskites. For example, Zr and Hf containing perovskites are susceptible to moisture, but when they are assembled by crown ethers, the air stability increased from one hour to a few days.

    [0152] Also provided herein are halide perovskite compounds and compositions (e.g., color luminescent compositions, semiconductor compositions) comprising the halide perovskite compounds generated by the methods provided herein.

    [0153] The metal halide perovskite compounds provided herein, e.g., according to the formula (crown ether@A).sub.2M(IV)X.sub.6, (crown ether@A)M(II)X.sub.4, or (crown ether@A)M(III)X.sub.5 can be used for a wide range of industrial utility. For example, the metal halide perovskite compounds provided herein can be used for high PLQY and tunable color luminescent materials. Commercial electronic display companies can adopt the material provided herein to create efficient and bright electronic displays, such as television and computer displays. When integrated with a UV light source, the combined system can generate emission of the specific color that has high (e.g., near-unity) PLQY and/or narrow emission peak (i.e., narrow FWHM).

    [0154] Further, when the high PLQY of the specific emission colors in the powders are preserved in thin films, it enables various optoelectronic device applications. Because the powders are stable in nonpolar organic solvents, they can be evenly dispersed into solution to form inks. The inks could be drop casted under ambient conditions, and, after rapid solvent evaporation, a uniform thin film forms. The emissive powders can also be processed with high-resolution 3D printing technologies after blending them uniformly into a monomer resin. A single 3D-printed structure can also manifest emissions in different colors by alternative resins during the printing procedure. The potential applications of 3D-printed light emitting structures are extensive and constantly evolving, ranging from intricate interior ambient-lighting solutions to seamless integration into wearable devices. Example 2 of the present disclosure provide example uses for the metal halide compounds provided herein.

    [0155] In the foregoing specification, the invention has been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of invention.

    EXAMPLES

    Example 1: Synthesis of (18C6@A).SUB.2.M(IV)X.SUB.6

    Structural Unit Formation in Solution

    [0156] The charge-neutral (18C6@A).sub.2M(IV)X.sub.6 dumbbell structural units are formed by dissolving 18C6 and A.sub.2M(IV)X.sub.6 in acetonitrile (ACN). This was verified using multiple solution-state characterization techniques, using (18C6@Cs).sub.2TeBr.sub.6 as an illustrating example. The NMR-active .sup.1H, .sup.79Br, and .sup.133Cs nuclei in the dumbbell structural unit experience different magnetic fields compared to the isolated nuclei (FIG. 2A-2C). The 24 homotopic protons on the 18C6 ring have identical NMR absorptions, at around 3.54 ppm in terms of a chemical shift. Once Cs.sup.+ is crowned, due to the partial removal of proton-electron density by the cation, the protons will be deshielded, and the chemical shift will increase to 3.59 ppm (FIG. 2A), consistent with reports that (18C6@Cs).sup.+ exists in ACN. However, with the addition of [TeBr.sub.6].sup.2 ionic octahedra, the chemical shift is further increased to 3.61 ppm. This increase indicated further withdrawal of electron density from the protons in the presence of [TeBr.sub.6].sup.2, which implied attachment to the (18C6@Cs)+ cations. .sup.79Br NMR revealed strong signals of free Br ions of CsBr in ACN, while the spin relaxation of .sup.79Br was quenched completely by Te.sup.4+ in Cs.sub.2TeBr.sub.6 (FIG. 2B) under the same measurement conditions most likely due to quadrupolar interaction. (18C6@Cs).sub.2TeBr.sub.6 in ACN showed the same quenching behavior as the Cs.sub.2TeBr.sub.6; the absence of .sup.79Br NMR signals confirmed that Br was coordinated to Te.sup.4+.

    [0157] To provide evidence that the dumbbell structural unit exists in ACN, .sup.133Cs NMR (FIG. 2C) was also conducted since Cs is the bridging atom that directly coordinates with both, Br of [TeBr.sub.6].sup.2 and O of 18C6. The free Cs chemical shift of CsBr was located at 38.81 ppm, while it was located at 35.56 ppm for Cs.sub.2TeBr.sub.6 in ACN. The 3.25 ppm difference in these controls indicated that the presence of Te.sup.4+ in the solution caused the peak to shift to lower ppm values. In contrast, a pronounced shielding effect was observed when Cs.sup.+ was crowned into (18C6@Cs).sup.+ in ACN, which suggested a withdrawal of electron density from the crown ether to Cs.sup.+, consistent with the .sup.1H NMR results. Adding [TeBr.sub.6].sup.2 into (18C6@Cs).sup.+ in ACN changed the Cs chemical shift from 22.22 to 22.97 ppm, which supported the formation of a new species, the dumbbell structural unit, distinct from its individual components. The dramatically broadened signal also supported the formation of a dumbbell as dipole-dipole interactions are introduced in slowly tumbling large-molecular weight species. The UV-vis spectrum of (18C6@Cs).sub.2TeBr.sub.6 precursors in ACN clearly shows the A, B, and C characteristic absorption bands of [TeBr.sub.6].sup.2 (FIG. 2D), indicating the presence of [TeBr.sub.6].sup.2 in solution. With the comprehensive measurements in .sup.1H, .sup.79Br, and .sup.133Cs NMR and UV-vis spectroscopy, the species were characterized in the solution phase, confirming the integrity of the dumbbell structural unit in solution (FIG. 1).

    Single-Crystal Characterization

    [0158] With the suspension of (18C6@A).sub.2M(IV)X.sub.6 units in ACN solution, the solid-state assembly was achieved, in the form of single crystals, with the introduction of antisolvents like diethyl ether. For example, the (18C6@Cs).sub.2TeCl.sub.6 single crystals have a parallelepiped shape, consistent with crystallographic symmetry, with a lateral dimension of approximately 300 m (FIG. 7). The structural details of the crystals were determined from single-crystal X-ray diffraction (SCXRD). (18C6@Cs).sub.2TeCl.sub.6 crystallized in the R-3 space group with lattice parameters of a=13.9378 and c=22.0396 (Table 1). The (18C6@Cs).sub.2TeCl.sub.6 dumbbell structural unit belonged to the S.sub.6 point group, where two Cs.sup.+ cations and the Te.sup.4+ cation sit on the S.sub.6 axis, and the six-fold symmetry of the 18C6 and the S.sub.6 axis of the O.sub.h-symmetric [TeCl.sub.6].sup.2 octahedron were perfectly aligned. In the (18C6@Cs).sub.2TeCl.sub.6 dumbbell unit, the TeCl bond length was determined as 2.546 , which was comparable to that in the Cs.sub.2TeCl.sub.6 vacancy-ordered double perovskite (2.570 )..sup.9 The high symmetry of this dumbbell building block offered a unique rhombohedral packing of the octahedra at the macroscopic level. Each [TeCl.sub.6].sup.2 octahedron occupied the b Wyckoff position of space group R-3 and was surrounded by six nearest octahedra at a TeTe distance of 10.9 , which was different from the fee packing in Cs.sub.2TeCl.sub.6 with a TeTe distance of 7.7 ..sup.9 The voids within the lattice are occupied by disordered solvent molecules. These tunable differences in the metal halide octahedron packing geometry may lead to differences in the overlap of molecular orbital wavefunctions, yielding unique electronic structures and optoelectronic properties that will be discussed later.

    Tunability of the Supramolecular Approach

    [0159] To demonstrate the general applicability of the approach provided herein, various crystals were produced through this supramolecular assembly strategy. In fact, the composition tunability of this new (18C6@A).sub.2M(IV)X.sub.6 structure is as rich as the tunabilities on A, M, and X sites in A.sub.2M(IV)X.sub.6 double perovskites. There are four compositional components in the (18C6@Cs).sub.2TeCl.sub.6 dumbbell structural unit which can be tuned by virtue of the precursors: (a) octahedron cations (M), (b) halide anions (X), (c) alkali metal cations (A), and (d) crown ethers (FIG. 3). Apart from [TeX.sub.6].sup.2, various tetravalent center cation octahedra, such as [SnX.sub.6].sup.2, [SeX.sub.6].sup.2, [IrX.sub.6].sup.2, [PtX.sub.6].sup.2, [ZrX.sub.6].sup.2, and [CeX.sub.6].sup.2 can also be assembled into similar dumbbell structural units with S.sub.6 symmetry. For typical 3D connected halide perovskites, such as low-T phase CsPbI.sub.3,.sup.36 due to the geometrical constraint imposed by the ionic framework sizes, such as the tolerance factor and proper bonding directions, a mismatched ionic size will lead to the breakdown or instability of the perovskite structure. In contrast, the isolated nature of the dumbbell structural units enables a more flexible control over the structure diversity without losing the prototypical crystal structure. Herein, a variety of unique dumbbell structures were achieved with the unique synthetic approach provided herein by simply changing the precursors. All structural details of the highly tunable (18C6@A).sub.2M(IV)X.sub.6 dumbbell structural units were obtained by powder XRD (PXRD) and SCXRD (Tables 1-7).

    [0160] The comparison of PXRD patterns for the seven different octahedron center cations (Te.sup.4+, Sn.sup.4+, Se.sup.4+, Ir.sup.4+, Pt.sup.4+, Zr.sup.4+, and Ce.sup.4+) is shown in FIG. 4A. Despite size differences between the different metal halide octahedral units, represented by the MCl bond length (from 2.324 to 2.555 ) summarized in FIG. 4B, they all had similar hexagonal PXRD patterns, with strong and distinct (101) and (110) diffraction peaks. In order to better evaluate the geometry of the dumbbell structural unit with various compositions, a simplified model made up of two cones and one octahedron was used (FIG. 8). A larger halide anion (from Cl.sup. to Br.sup. to I.sup.) leads to a larger octahedron size (FIG. 4D), and the length of the dumbbell structural unit increases in all three dimensions, reflected by the shifting of all diffraction peaks to lower 2 values (FIG. 4C). Although the bromide version remained in the R-3 space group (Table 2), the iodide version deviated from the hexagonal symmetry and crystallized in the monoclinic crystal system with the space group of P21/m (Table 7 and FIG. 9) due to the larger size of the iodide anion. On the contrary, it was found that the MX bonds were not influenced by the alkali metal cations, and the R-3 space group can be preserved. FIG. 4F shows that the TeCl bond lengths were 2.546 , 2.548 , and 2.544 for the Cs-, Rb-, and K-based assemblies, respectively. However, when using a smaller alkali cation, the height of the cone decreased (from 2.4 to 1.8 when changing from Cs.sup.+ to K.sup.+), while the diameter of the cone remained nearly unchanged. This height decrease was consistent with a shift in the diffraction peaks related to the c lattice parameter [such as (101) and (104) planes] to larger 2 values. In contrast, the diffraction of facets parallel to the c axis, such as the (110) plane, has almost no shift (FIGS. 4E, 10, 11). The single crystals of (18C6@K).sub.2TeBr.sub.6 synthesized from ACN and DMF were compared (Table 8); both crystals are in the R-3 space group and only show slight differences in lattice parameters, which are attributed to the occupation of disordered larger DMF molecules compared to ACN molecules in the voids within the lattice. Thermogravimetric analysis on (18C6@Cs).sub.2TeCl.sub.6 shows that the total relative mass changes from 98.5% [M.sub.w=1248.95 g/mol for (18C6@Cs).sub.2TeCl6.Math.2DMF] to 88.6% [M.sub.w=1134.76 g/mol for (18C6@Cs).sub.2TeCl.sub.6] from 80 to 120 C. and further reduced to 48.9% (M.sub.w=606.13 g/mol for Cs.sub.2TeCl.sub.6) from 160 to 220 C. (FIG. 12). The same decomposition process is also verified for (18C6@Cs).sub.2SnCl.sub.6 and (18C6@Cs).sub.2TeBr.sub.6. Thermal analysis studies reveal the fact that for this family of new materials, the solvent molecules (such as DMF) occupying the lattice voids are evaporated from 80 to 120 C., and 18C6 starts to detach at roughly 160 C. and completely decomposes into the corresponding all-inorganic Cs.sub.2MX.sub.6 powders after 220 C. It also proves the existence of solvent molecules in the lattice voids as expected from the single-crystal structure studies. To further confirm the intact O.sub.h symmetry of the metal halide octahedral building blocks, Raman spectroscopy was used to study the vibrational modes of the dumbbell structural unit. Previous Raman studies of the Cs.sub.2TeCl.sub.6 crystal system determined that the vibrational units in the single crystals were the isolated [TeCl.sub.6].sup.2 octahedra with Oh point group symmetry (FIG. 13). All three characteristic Raman peaks were still observed in the (18C6@A).sub.2TeCl.sub.6 single crystals (FIG. 14), confirming the O.sub.h symmetry of the [TeCl.sub.6].sup.2 unit in the dumbbell building block. Similar Oh-symmetry Raman peaks were also observed in assembled crystals with other octahedra, such as [TeBr.sub.6].sup.2, [SnCl.sub.6].sup.2, and [SnBr.sub.6].sup.2 (FIGS. 15-17).

    [0161] The compatibility between the point groups of 18C6 and the metal halide octahedral units resulted in the rhombohedral R-3 space group of the assembled single crystals. By breaking the six-fold symmetry of the crown ether, the supramolecular approach can realize more packing geometries for these metal halide octahedral units. For example, the larger 21-Crown-7 (21C7) had to distort itself to coordinate with the center Cs.sup.+ cation (FIG. 18A). Such distortion of the dumbbell building block dramatically altered the packing geometry of these building blocks (FIG. 18B, 18C). Single crystals of (21C7@Cs).sub.2TeBr.sub.6 and (21C7@Cs).sub.2TeI.sub.6 crystallized in an orthorhombic structure with space group Cmc21 (Table 9). The [TeBr.sub.6].sup.2 units in the (21C7@Cs).sub.2TeBr.sub.6 dumbbell unit were still nearly perfect, but this distorted dumbbell structure was found to be horizontally packed into a two-dimensional (2D) array form. In each [TeBr.sub.6].sup.2 octahedral plane, one octahedron had four nearest neighbors (the TeTe distance is 9.9 ), with no solvent molecules or crown ether complexes in between. The interlayer spacing of the 2D octahedral sheets was about 13.7 . Consistent with a 2D structure, the (002) diffraction peak was much stronger than the other diffraction peaks (FIG. 19). The single crystal had a planar shape with a width of over 400 m and a thickness of only 35 m (FIGS. 20, 21). Therefore, the use of 21C7 introduced another new type of metal halide octahedral unit packing in the supramolecular assemblies provided herein.

    Optoelectronic Properties of the Supramolecular Assemblies

    [0162] The demonstrated synthetic flexibility and systematic control of the crystal structures assembled from the dumbbell structural unit have deep implications for their electronic properties. The electronic structure of the structural unit is primarily determined by the metal halide octahedral units..sup.14 For instance, by tuning the center metal cation of the [M(IV)Cl.sub.6].sup.2 (M=Sn.sup.4+, Te.sup.4+, Ce.sup.4+, and Ir.sup.4+) ionic octahedron, the optical absorption onset of the supramolecular-assembled crystals varied from 660 nm for [IrCl.sub.6].sup.2 to 500 nm for [CeCl.sub.6].sup.2, to 460 nm for [TeCl.sub.6].sup.2, and to 310 nm for [SnCl.sub.6].sup.2 (FIG. 5A). The differences in absorption features for these four ionic octahedra are due to their different electronic configurations. Te.sup.4+ is a cation with ns2 electronic configuration; the absorbance of [TeCl.sub.6].sup.2 octahedra was dominated by the molecular 5s to 5s5p transitions, represented as the A, B, and C bands. Recent studies suggested that a sharp absorption band in the UV range for [SnCl.sub.6].sup.2 can be assigned to a ligand-to-metal charge transfer (LMCT) transition. The absorption band was also assigned to the LMCT transition for [CeCl.sub.6].sup.2. For Ir, the subshells of the 5d orbitals of Ir.sup.4+ in [IrCl.sub.6].sup.2 contributed to the weak optical transition bands, and intense bands were due to metal-ligand interactions. Changing the halide anions also contributed to different optical absorptions. (18C6@Cs).sub.2TeX.sub.6 (X=Cl.sup., Br.sup., I.sup.) structural units have vastly different optical absorption features due to the shift of the atomic orbital energy levels of halide anions (FIG. 5B).

    [0163] The optoelectronic tunability of the dumbbell unit can be achieved not only by incorporating various [M(IV)X.sub.6].sup.2 ionic octahedra but also by changing the octahedral packing geometries and the surrounding coordination environment of the same metal halide octahedra. The electronic interaction of these octahedral units has deep implications for the electronic structure of the crystal. According to the tight-binding model, the superposition of wavefuinctions for isolated atoms will be greater when atoms are brought closer together in a solid, so the electronic bands will be more dispersive, and the band gap will decrease..sup.41 In the current materials system, the individual octahedron can be viewed as a super ion/atom with specific molecular orbital levels. When the octahedra of these dumbbell units are closer to each other, their orbital wavefunctions will overlap to a greater extent. This was confirmed by the experimental observation provided herein. The UV-vis absorption spectra of four different packing geometries of the [TeBr.sub.6].sup.2 octahedra are shown in FIG. 5C. As the [TeBr.sub.6].sup.2 octahedra were packed closer in a crystal by using different crown ether complexes, the A-band absorption onset red-shifted from 500 to 590 nm, causing the crystal to change color from orange [(18C6@Cs).sub.2TeBr.sub.6 and (21C7@Cs).sub.2TeBr.sub.6] to red [Cs.sub.2TeBr.sub.6] (FIG. 22).

    [0164] The supramolecular-assembled crystals have not only tunable optical absorption but also strong photoluminescence (PL) with a highly tunable emission color. For instance, under 250 nm excitation, (18C6@Cs).sub.2ZrCl.sub.6 displays an intense blue emission at 459 nm, with a full width at half-maximum (FWHM) of 0.90 eV. The PL quantum yield of (18C6@Cs).sub.2ZrCl.sub.6 is 12.57%, which is calculated from integrating sphere measurements. Apart from high emission intensities, the supramolecular approach can also enable the fine-tuning of the emission color. The strong coupling of the exciton with lattice vibrations will greatly lower the energy level of the exciton, forcing it into transient self-trapped exciton (STE) states with a range of self-trapped energy levels. The [TeCl.sub.6].sup.2 octahedron was selected to study the STE emission of the dumbbell structural units. The PL spectra (FIGS. 5 and 23) of the (18C6@A).sub.2TeCl.sub.6 (A=K.sup.+, Rb.sup.+, and Cs.sup.+) crystals had emission peak wavelengths at 604, 642, and 659 nm, respectively. They all featured a large Stokes shift of 1.13, 1.26, and 1.31 eV, respectively, and a very large broadband emission. The PL FWHM was 0.44, 0.54, and 0.55 eV, respectively. The Stokes shift was larger than that of the Cs.sub.2TeCl.sub.6 crystal, with a value of 1.04 eV,.sup.9 which indicated a greater exciton-phonon coupling effect. Furthermore, the Stokes shift increased with increasing alkali metal cation size. This phenomenon was likely due to the difference in the alkali metal halide bond strength. A weaker or softer alkali metal halide bond will force the excitonic state into deeper self-trapped levels. The PL studies demonstrate that the supramolecular assembly approach can be used to design emissive and tunable emitters.

    SUMMARY

    [0165] In conclusion, a general synthetic strategy for a library of new supramolecular building blocks (crown-ether@A).sub.2M(IV)X.sub.6, constructed from ionic halide perovskite octahedral units and crown ethers was demonstrated. The great tunability of (crown-ether@A).sub.2M(IV)X.sub.6 can be explored along (1) changing the octahedron cation, (2) tuning the halide anion, (3) modifying the alkali metal cation coupled with the crown ether, and (4) varying the size of the crown ether. Based on the structural diversity of the supramolecular assembly approach, one-dimensional and 2D electronic dimensionality solid assembly with connected [MX.sub.6].sup.n octahedra is tested. Also, with all these synthetic possibilities, a more in-depth study of the optoelectronic properties of the ionic octahedral building blocks can be conducted. This new assembly strategy of the supramolecular building blocks could bring a new general method for halide perovskite material discovery.

    Materials and Methods

    [0166] Materials. 18-Crown-6 (18C6, 99%, Sigma Aldrich), 21-Crown-7 (21C7, 97%, Alfa Chemistry), CsCl (99.999%, Sigma Aldrich), CsBr (99.999%, Sigma Aldrich), CsI (99.999%, Sigma Aldrich), RbCl (99.95%, Sigma Aldrich), RbBr (99.6%, Sigma Aldrich), RbI (99.9%, Sigma Aldrich), KCl (99%, Sigma Aldrich), KBr (99%, Sigma Aldrich), KI (99%, Sigma Aldrich), TeCl.sub.4 (99.9%, Alfa Aesar), TeBr.sub.4 (99.9%, Alfa Aesar), TeI.sub.4 (99%, Alfa Aesar), SnCl.sub.4 (99.9%, Alfa Aesar), SnBr.sub.4 (99.9%, Alfa Aesar), K.sub.2PtCl.sub.6 (99.99%, Sigma Aldrich), K.sub.2IrCl.sub.6 (99.99%, Sigma Aldrich), SeCl.sub.4 (35.0-36.5% Se basis, Sigma Aldrich), ZrCl.sub.4 (99.99%, Sigma Aldrich), (NH.sub.4).sub.2Ce(NO.sub.3).sub.6 (99.99%, Sigma Aldrich), hydrochloric acid (HCl, 37%, Sigma Aldrich), hydrobromic acid (HBr, 48%, Sigma Aldrich), hydroiodic acid (HI, 57%, Sigma Aldrich), N,N-dimethylformamide (DMF, Fisher Scientific), acetone (Sigma Aldrich), acetonitrile (ACN, Sigma Aldrich), acetonitrile-d.sub.3 (ACN-d.sub.3, 99.8 atom % D, Sigma Aldrich) and diethyl ether (DEE, Sigma Aldrich) were used as received without further purification or modification.

    [0167] Synthesis of A.sub.2MX.sub.6 (A=Cs.sup.+, Rb.sup.+, K.sup.+; M=Te.sup.4+, Sn.sup.4+, Zr.sup.4+; X=Cl.sup., Br.sup., I.sup.) Powders. Precursor powders AX and MX4 were measured into a 20 ml vial based on the 2:1 stoichiometric ratio, and the precursors were dissolved in 5 ml of HX acid. Precipitates were filtered immediately and washed with HX acid. Precipitates were dried in a vacuum oven at 60 C. overnight.

    [0168] Synthesis of K.sub.2SeCl.sub.6 Powders. Precursor powders KCl and SeCl.sub.4 were measured into a 20 ml vial based on the 2:1 stoichiometric ratio, and the precursors were dissolved in 5 ml of DMF on a hot plate at 100 C. for three hours in an argon glovebox. The supersaturated solution was filtered into a new 20 ml vial and 10 ml of DEE was added into the solution as anti-solvent. Precipitates were filtered, washed with acetone and dried in the vacuum oven at 60 C. overnight.

    [0169] Synthesis of Cs.sub.2CeCl.sub.6 Powders. Cs.sub.2CeCl.sub.6 powders were synthesized using the same procedure as literature.sup.1. Precursor powders of CsCl and (NH.sub.4).sub.2Ce(NO.sub.3).sub.6 based on the 2:1 stoichiometric ratio were dissolved in 4 ml of HCl at 4 C. The precipitate was filtered immediately and washed with 1 ml of cooled HCl. The precipitate was dried in vacuum oven at room temperature overnight.

    [0170] Synthesis of (18C6@A).sub.2M(IV)X.sub.6 (A=Cs.sup.+, Rb.sup.+, K.sup.+; M=Te.sup.4+, Sn.sup.4+, Se.sup.4+, Ir.sup.4+, Pt.sup.4+, Zr.sup.4+, Ce.sup.4+; X=Cl.sup., Br.sup., I.sup.). Powders of A.sub.2MX.sub.6 and 18C6 were measured into a 20 ml vial based on the 1:2 stoichiometric ratio, and the precursors were dissolved in 10 ml of ACN or DMF on a hot plate at 100 C. with vigorous stirring for three hours. The supersaturated solution was filtered into a new 20 ml vial. (18C6@A).sub.2M(IV)X.sub.6 powders were obtained by adding 10 ml of the supersaturated solution into 20 ml of DEE anti-solvent in a 50 ml centrifuge tube. The mixtures were centrifuged at 4000 rpm for 5 minutes to separate the powders and the solution. The powders were dried in a vacuum oven at 50 C. overnight. Se.sup.4+ and Zr.sup.4+ versions were hydroscopic, and an argon glovebox was used to avoid air exposure during the whole process. using the solution-based anti-solvent vapor method. (18C6@A).sub.2M(IV)X.sub.6 single crystals were grown using an anti-solvent diffusion method. 1 ml of the abovementioned supersaturated solution was added into a 4 ml vial, which was placed into a 20 ml vial with 4 ml of DEE. After approximately two days, single crystals were formed on the bottom and the wall of the 4 ml vial. Single crystals were washed 3 times with acetone and stored in an argon glovebox for future use.

    [0171] Synthesis of (21C7@Cs).sub.2TeX.sub.6 (X=Br.sup., I.sup.). (21C7@Cs).sub.2TeX.sub.6 (X=Br.sup., I.sup.) powders and single crystals were synthesized using methods similar as the (18C6@A).sub.2M(IV)X.sub.6 but replacing 18C6 with 21C7.

    [0172] Single-Crystal X-ray Diffraction (SCXRD). The SCXRD data were collected at the Small Molecule X-ray Crystallography Facility (CheXray) in College of Chemistry, UC Berkeley. SCXRD were measured with a Rigaku XtaLAB P200 instrument equipped with a MicroMax-007 HF microfocus rotating anode and a Pilatus 200K hybrid pixel array detector using monochromated Mo K radiation (=0.71073 ). All crystal datasets were collected at room temperature (298 K). CrysAlisPrO.sup.2 was used for data collection and data processing, including a multi-scan absorption correction applied using the SCALE3 ABSPACK scaling algorithm within CrysAlisPro. Using Olex2.sup.3, the structures were solved with the SHELXT.sup.4 structure solution program using Intrinsic Phasing and refined with the SHELXL.sup.5 refinement package using Least Squares minmization. Due to the occupation of disordered two solvent molecules in the crystal voids, solvent masks were used during the refinement. All reflections where [error/esd]>5 were omitted, as the existence of disordered molecules will result in high error/esd values in low d-spacing diffractions.

    [0173] Ambient Condition Powder X-ray Diffraction. Powder X-ray diffraction (PXRD) data of (18C6@A)2MX6 (A=Cs.sup.+, Rb.sup.+, K.sup.+; M=Te.sup.4+, Sn.sup.4+, Ir.sup.4+, Pt.sup.4+, Zr.sup.4+, Ce.sup.4+; X=Cl.sup., Br.sup., I.sup.) and (21C7@Cs)2TeX6 (X=Br.sup., I.sup.) were collected using a Bruker D8 laboratory diffractometer with a Cu K radiation source in ambient condition. Data was collected from 2 =7-50. The single crystals were ground into powders and transferred onto glass for measurements.

    [0174] Inert Atmosphere Powder X-ray Diffraction. PXRD of (18C6@K).sub.2SeCl.sub.6 was collected using a Rigaku Miniflex 6G Benchtop Powder XRD with a Cu K radiation source and an inert atmosphere sample holder. The powder samples were loaded onto the sample holder inside an argon glovebox.

    [0175] Optical Microscope Imaging. An unpolarized, white-light optical microscope was used to visualize single crystals under either a 20 or a 50 microscope objective. The single crystals were observed under dark-field imaging. The single crystals were dispersed onto glass for measurement.

    [0176] Scanning Electron Microscopy (SEM). A field-emission SEM (FEI Quanta 3D FEG SEM/FIB) was used to visualize single crystal morphologies at the QB3-Berkeley Biomolecular Nanotechnology Center (BNC).

    [0177] Nuclear Magnetic Resonance Spectroscopy. All the NMR experiments were conducted in UC Berkeley's NMR facility in the College of Chemistry (CoC-NMR). The .sup.1H and .sup.79Br solution NMR were performed by Bruker AV600 and .sup.133Cs solution NMR was performed by Bruker AV500. Acetonitrile-d3 was used as solvent for all the measurements.

    [0178] Raman Spectroscopy. The Raman spectra of Cs.sub.2TeCl.sub.6, (18C6@A).sub.2TeBr.sub.6, (18C6@A).sub.2SnCl.sub.6, and (18C6@A).sub.2SnBr.sub.6 (A=K.sup.+, Rb.sup.+, Cs.sup.+) samples were measured by a confocal Raman microscope system (Horiba LabRAM HR800 Evolution). The single crystals were dispersed onto glass microscope slides for measurement. A continuous-wave (cw) 633 nm laser was focused onto a crystal facet at a constant power density set by neutral density filters. The Raman signal from the sample was collected using a microscope objective in a backscattering geometry (100, NA 0.6). High-resolution Raman spectra were measured with a charge-coupled device (CCD) detector equipped with a diffraction grating of 1800 gr/mm and a long pass filter (80 cm.sup.1) to remove the Rayleigh scattering line from the signal.

    [0179] Ultralow-Frequency (ULF) Raman Spectroscopy. The Raman spectra of the (18C6@A).sub.2TeCl.sub.6 (A=K.sup.+, Rb.sup.+, Cs.sup.+) samples were measured by a confocal Raman microscope system (Horiba LabRAM HR Evolution) at the Stanford Nano Shared Facilities (SNSF). The powders were dispersed onto glass microscope slides for measurement. A continuous-wave 633 nm laser was focused onto the powder, thin film, or coating surfaces at a constant power density set by neutral density filters. The Raman signal from the sample was collected using a microscope objective in a back-scattering geometry (100, NA 0.6). High-resolution Raman spectra were measured with an Andor Newton DU970P BVF EMCCD detector equipped with a diffraction grating of 1800 gr/mm and an ULF filter package (10 cm.sup.1) to remove the Rayleigh scattering line from the signal.

    [0180] Photoluminescence (PL) Spectroscopy. Photoluminescence measurements were collected with a home-built PL microscope system. The single crystals were dispersed onto glass for measurement. A continuous-wave solid-state 375 nm laser (Coherent OBIS 375LX) was focused obliquely onto the sample with a constant power density in visible wavelength measurements and infrared wavelength measurements, which was set by neutral density filters. The PL signal from the sample was collected using a microscope objective (50) coupled to a long-pass filter (390 nm) in visible wavelength measurements and to a long-pass filter (800 nm) in infrared wavelength measurements to remove the laser line from the signal. Visible wavelength PL spectra were collected under a 1 s exposure time with a Si CCD detector cooled to 120 C. via liquid nitrogen and equipped with a diffraction grating of 150 gr/mm. The PL imaging was taken under bright-field conditions.

    [0181] Photoluminescence Quantum Yield (PLQY). The PLQY was calculated from integrating sphere measurements in an Edinburgh Instruments FS5 spectrofluorometer with 250 nm excitation. The single crystals were grinded into powders, and a thin layer of powders was placed in the polytetrafluoroethylene (PTFE) sample holder for measurement. A 150 W continuous-wave (CW) ozone-free Xenon (Xe) arc lamp was focused onto the sample. The spectra were collected under a 0.3 s exposure time with a UV enhanced Si photodiode array equipped with a diffraction grating of 1200 gr/mm.

    [0182] UV-Visible Absorption Spectroscopy. The absorption spectra of the samples were measured by a UV-visible spectrophotometer (Shimadzu UV-2600). Data was collected in absorption mode over a wavelength range of 200 nm and 900 nm with a medium scanning rate. The powder samples were widely dispersed on quartz glass. The solution samples were placed into a quartz cell with a 0.1 mm path length.

    [0183] Thermogravimetric Analysis. The measurement was performed by TA Instrument Q500 with a nitrogen atmosphere. The samples were loaded on a platinum pan. The experiment procedure was 1) equilibrate at 60 C. for 20 minutes and 2) ramp to 500 C. with a heating rate of 5 C./min.

    Example 2: Supramolecular Assembly of Blue and Green Halide Perovskites with Near-Unity Photoluminescence

    [0184] As shown in Example 1, in a general crown ether-assisted supramolecular assembly approach for tetravalent metal octahedra provided herein, two crown ether@alkali metal complexes can sandwich a tetravalent metal octahedron into a (crown ether@A).sub.2MX.sub.6 dumbbell structural unit. The composition of the dumbbell structural unit is highly tunable, with crown ether=18-crown-6 (18C6) or 21-crown-7 (21C7); A=Cs.sup.+, Rb.sup.+, or K.sup.+; M=Te.sup.4+, Sn.sup.4+, Se.sup.4+, Ir.sup.4+, Pt.sup.4+, Zr.sup.4+, Hf.sup.4+, or Ce.sup.4+; and X=Cl.sup., Br.sup., or I.sup.. In Example 2, this general supramolecular assembly approach was extended to [HfBr.sub.6].sup.2 octahedra to achieve a structure with formula (18C6@K).sub.2HfBr.sub.6 that features blue emission with near-unity (96.2%) PLQY. The synthetic route was optimized by replacing the challenging high-temperature solid-state synthesis with a low-temperature organic solution-based synthesis. Moreover, an efficient green emission was also achieved by tuning the composition of the (crown ether@A).sub.2MX.sub.6 dumbbell structural unit. (18C6@K).sub.2ZrCl.sub.4Br.sub.2 demonstrated green emission with 82.7% PLQY. By studying the photophysics of the supramolecular assembled samples, the emission was attributed to STE states, and a very strong electron-phonon coupling constant (represented by the Huang-Rhys parameter) of >90 for (18C6@K).sub.2HfBr.sub.6 was observed. The supramolecular assembled samples had longer PL lifetimes (in the microsecond timescale) compared with those of other halide perovskite systems that reflected a low rate of nonradiative recombination.

    [0185] The structural integrity and impressive optical properties of the supramolecular assembled solid powders were further maintained by generating a powder suspension in nonpolar organic solvents, such as dichloromethane (DCM), to create an ink system. Polystyrene (PS) polymer was dissolved into the ink to further increase the solution processability. These inks were used to fabricate thin films through fast solvent evaporation. In combination with a digitally controlled excitation source, the (18C6@K).sub.2HfBr.sub.6/PS composite thin film could be used as a display with bright color contrast and fast response time. A solution-processable ink also allowed three-dimensional (3D) printing of the powders into various blue-, green-, and dual-color-emitting structures.

    Crown Ether-Assisted Supramolecular Assembly

    [0186] A supramolecular synthetic route was explored in which 18C6 greatly increased the solubility of the KBr and HfBr4 precursors in polar organic solvents for low-temperature solution based synthesis. A clear precursor solution was obtained with acetonitrile (ACN) at 80 C. with the concentration of 4 mM for 18C6 and KBr and 2 mM for HfBr.sub.4. Example 1 indicated that a (18C6@K).sub.2HfBr.sub.6 dumbbell structural unit was formed in ACN. (18C6@K).sub.2HfBr.sub.6 powders and single crystals were grown using the antisolvent crystallization method (39). K.sub.2HfBr.sub.6 powders were also synthesized by using a modified solid-state synthesis method. The purity was increased and the synthesis temperature was decreased to 200 C. by combining mechanical forces with heat to facilitate solid-state diffusion. Details of the synthesis for (18C6@K).sub.2HfBr.sub.6 and K.sub.2HfBr.sub.6 are described in the Materials and Methods section.

    [0187] The crystal structure of (18C6@K).sub.2HfBr.sub.6 was determined from single-crystal x-ray diffraction (SCXRD). (18C6@K).sub.2HfBr.sub.6 crystallized in the R-3 space group with lattice parameters of a=14.1332 and c=21.0189 (FIG. 24 and table 10). The (18C6@K).sub.2HfBr.sub.6 dumbbell structural unit belongs to the S6 point group, where two K.sup.+ cations and the Hf.sup.4+ cation sit on the S.sub.6 axis. The sixfold symmetry axis of the 18C6 and the S.sub.6 axis of the O.sub.h-symmetric [HfBr.sub.6].sup.2 octahedron were aligned (FIG. 24B). The K.sub.2HfBr.sub.6 crystals were face-centered cubic (fcc) (FIG. 24C), in which the [HfBr.sub.6].sup.2 ionic octahedra were charge balanced by the surrounding K.sup.+ cations (FIG. 24D).

    [0188] The purity of the (18C6@K).sub.2HfBr.sub.6 and K.sub.2HfBr.sub.6 powders was investigated with powder x-ray diffraction (PXRD) (FIG. 24E). The PXRD pattern of the (18C6@K).sub.2HfBr.sub.6 powders matched with the calculated pattern generated from the single-crystal structure with no visible diffraction peaks from impurities. The quality of the PXRD pattern for the K.sub.2HfBr.sub.6 powders was much lower because of their extreme air sensitivity. The measurement had to be collected in 5 min with an inert atmosphere sample holder to prevent the degradation of the powders and measurement of the degradation product. Although the quality of the K2HfBr.sub.6 PXRD pattern was not ideal, the most dominant peaks of the fcc K.sub.2HfBr.sub.6 phase were still identifiable. Moreover, no HfBr4 or KBr diffraction peaks were present (FIG. 24E), which showed that all of the precursor materials transformed into the K.sub.2HfBr.sub.6 phase. A Raman spectrum of K.sub.2HfBr.sub.6 further confirmed the presence of the [HfBr.sub.6].sup.2 octahedra in the crystal structure (FIG. 29).

    [0189] The crown ether-assisted supramolecular approach was generalized to produce other emissive centers. For example, (18C6@K).sub.2ZrBr.sub.6 single crystals and powders were successfully synthesized by the same method, and the same crystal structure as (18C6@K).sub.2HfBr.sub.6 was obtained (FIG. 30 and table 10). FIG. 31 shows that phase-pure (18C6@K).sub.2ZrBr.sub.6 powders could be obtained with the established solution-based synthesis. K.sub.2ZrBr.sub.6 powders were also synthesized with the same solid-state method as K.sub.2HfBr.sub.6. The (18C6@K).sub.2HfBr.sub.6 and (18C6@K).sub.2ZrBr.sub.6 dumbbell building blocks were also the electronic units of the new crystal. To elucidate the effect of 18C6 on the electronic structures of the assembled [HfBr.sub.6].sup.2 octahedra, density functional theory (DFT) calculations were performed on (18C6@K).sub.2HfBr.sub.6 (FIG. 24F) and K2HfBr.sub.6 (FIG. 24G) to determine their electronic band structures and partial electronic density of states (pDOS). The electronic bands of (18C6@K).sub.2HfBr.sub.6 were less dispersive compared with K2HfBr.sub.6 because the [HfBr.sub.6].sup.2 octahedra were more separated in (18C6@K).sub.2HfBr.sub.6. The conduction band (CB) of (18C6@K).sub.2HfBr.sub.6 was composed of Hf 5d and Br 4p orbitals, as was the CB of K.sub.2HfBr.sub.6. However, the valence band (VB) compositions were quite different in these two materials. The VB of K.sub.2HfBr.sub.6 was mainly composed of the Br 4p orbital, but 18C6 contributed to the VB of (18C6@K).sub.2HfBr.sub.6. Thus, the 18C6 molecules were electronically coupled to the [HfBr.sub.6].sup.2 octahedra, which indicates that the entire (18C6@K).sub.2HfBr.sub.6 dumbbell building block became a new electronic unit. DFT calculations of (18C6@K).sub.2ZrBr.sub.6 showed that the contribution from 18C6 to the VB and the band structures were more discrete than those in K.sub.2ZrBr.sub.6 (FIG. 32).

    Optical Characterization of the Blue and Green Emitters

    [0190] Compared with K.sub.2HfBr.sub.6, (18C6@K).sub.2HfBr.sub.6 had greatly enhanced emission intensity. FIG. 25A shows the extremely bright blue emission of (18C6@K).sub.2HfBr.sub.6 powders under 254-nm ultraviolet (UV) excitation. The photoluminescence (PL) spectrum of (18C6@K).sub.2HfBr.sub.6 powders was measured at 275-nm excitation (FIG. 25B). The powders had a blue emission centered at 445 nm (2.79 eV), and the full width at half maximum (FWHM) was 0.73 eV. Photoluminescence excitation (PLE) spectra revealed a large Stokes shift (1.35 eV).

    [0191] The emission intensity of the (18C6@K).sub.2HfBr.sub.6 powders was quantified with PLQY measurement, and a near-unity value of 96.21.2% was obtained for the (18C6@K).sub.2HfBr.sub.6 powders over six measurements from two batches of samples (FIG. 33). The specific value for each measurement is shown in table S2. By contrast, the PLQY of K.sub.2HfBr.sub.6 powders was 12.8% (FIG. 34). K.sub.2HfBr.sub.6 also had an even larger Stokes shift (1.42 eV) and broader emission, with a peak emission wavelength of 457 nm and a FWHM of 0.90 eV (FIG. 35). The color purity of the emission from the [HfBr.sub.6].sup.2 octahedra was also enhanced by the supramolecular approach. FIG. 36 shows the emission color of (18C6@K).sub.2HfBr.sub.6 and K.sub.2HfBr.sub.6 powders on the CIE 1931 chromaticity diagram. (18C6@K).sub.2HfBr.sub.6 had a much purer blue emission color compared with K.sub.2HfBr.sub.6.

    [0192] The [ZrBr.sub.6].sup.2 units enabled high-PLQY green emissions. Upon 290-nm excitation, (18C6@K).sub.2ZrBr.sub.6 had a PL peak at 547 nm, and the FWHM of the PL was 0.69 eV (FIG. 37). For the same excitation wavelength, the PL peak of K.sub.2ZrBr.sub.6 was at 560 nm, and the FWHM of the PL was 0.70 eV (FIG. 38). The PLQY of (18C6@K).sub.2ZrBr.sub.6 was 49.8% (FIG. 39), which was slightly greater than the PLQY of K.sub.2ZrBr.sub.6 (46.3%) (FIG. 40). Although the peak position of the PL spectrum was in the green region, simply analyzing the peak emission wavelength was insufficient given the broadness of the STE-based emission because this crystal actually produced a yellow-green emission color (FIG. 41).

    [0193] Given the great chemical tunability of the dumbbell structural unit, an alloying approach at the halide site was proposed to achieve a purer green emission with near-unity PLQY. For CsPbX.sub.3 (where X=Cl.sup., Br.sup., or I.sup.) nanocrystals, the emission color can be easily controlled by tuning the halide composition; introducing Cl.sup. in the halide site may generate a shorter wavelength emission color. By carefully tuning the KCl/KBr and ZrCl.sub.4/ZrBr.sub.4 precursor ratio in the synthesis, the Cl.sup./Br.sup. ratio in the obtained (18C6@K).sub.2ZrX.sub.6 dumbbell structural unit can be precisely controlled. As expected, a larger Cl.sup./Br.sup. ratio created a more blue-shifted PL (FIGS. 42 and 43). For example, (18C6@K).sub.2ZrCl.sub.3Br.sub.3 and (18C6@K).sub.2ZrCl.sub.4Br.sub.2 had green emission with PL peaks at 534 and 530 nm, respectively. Increasing the Cl.sup. content to a composition of (18C6@K).sub.2ZrCl.sub.4.5Br.sub.1.5 changed the PL color to a cyan (bluish green) color. The established halide site alloying approach not only generated a purer green emission color but also boosted the PLQY of the emission to near-unity. For the Cl.sup./Br.sup. ratio from 1:1 to 2:1 to 3:1, the PLQYs were 69.1, 82.7, and 87.0%, respectively (FIGS. 44 and 45).

    [0194] Because the 2:1 Cl.sup./Br.sup. ratio composition had both pure-green emission color and high PLQY, (18C6@K).sub.2ZrCl.sub.4Br.sub.2 was selected for detailed studies of green emission. (18C6@K).sub.2ZrCl.sub.4Br.sub.2 single crystals were synthesized by controlling the Cl.sup./Br.sup. precursor ratio to be 2:1. The formula of (18C6@K).sub.2ZrCl.sub.4Br.sub.2 was determined by SCXRD (Cl.sup.:Br.sup.=4.3:1.7) (FIG. 46 and table 12) and energy-dispersive x-ray spectroscopy (EDX) elemental mapping (Cl.sup.:Br.sup.=4.1:1.9) (FIG. 47). The Cl and Br atoms were perfectly miscible in the crystal structure. PXRD of the (18C6@K).sub.2ZrCl.sub.4Br.sub.2 powders (FIG. 48) also indicated that this composition was a phase-pure system. The (101) and (110) diffraction peaks of (18C6@K).sub.2ZrCl.sub.4Br.sub.2 were slightly shifted to larger 2 values compared with the corresponding PXRD peaks of (18C6@K).sub.2ZrBr.sub.6, which suggests smaller lattice constants (FIG. 49).

    [0195] FIG. 25C shows the bright green emission of (18C6@K).sub.2ZrCl.sub.4Br.sub.2 powders under 302-nm UV lamp excitation. The PL spectrum of (18C6@K).sub.2ZrCl.sub.4Br.sub.2 powders was measured at 295-nm excitation (FIG. 25D). The green emission had a similar Stokes shift (1.36 eV versus 1.35 eV) and FWHM (0.80 eV versus 0.73 eV) compared to the blue emission of the (18C6@K).sub.2HfBr.sub.6 powders, which suggests similar emission properties of the Hf and Zr metal centers in the supramolecular assembly materials system. The PLQY of the emission from (18C6@K).sub.2ZrCl.sub.4Br.sub.2 powders was 82.70.9%, which was determined through the measurement of four samples from two batches (table S4). Therefore, highly emissive powders with blue and green emission colors were achieved based on the supramolecular assembly approach. The blue and green colors of the emissions from (18C6@K).sub.2HfBr.sub.6 and (18C6@K).sub.2ZrCl.sub.4Br.sub.2, respectively, are summarized in the CIE 1931 diagram (FIG. 25E).

    [0196] Next, a comprehensive photophysics analysis was conducted to confirm and gain deeper insights into the STE emission mechanism that underlies these blue and green emissions. The distinctive features of STE emissions, including their large Stokes shift and broadband nature, are primarily attributed to the electron phonon coupling effect. To unravel the STE emission mechanism, low temperature PL measurements was conducted to examine the electron-phonon coupling in (18C6@K).sub.2HfBr.sub.6. With increasing temperatures, the PL peak gradually broadened, and the peak was slightly red-shifted, indicating greater phonon participation at higher temperatures (FIG. 36A). A small shoulder peak at 550 nm was present that was especially distinct at lower temperatures, which is attributed to the Zr impurity in the HfBr4 precursor (35). Inductively coupled atomic emission spectroscopy revealed an 0.5 atomic % (at %) ZrBr.sub.4 impurity in the as obtained HfBr.sub.4 precursor, and that there was an 0.6 at % Zr.sup.4+ impurity in the synthesized (18C6@K).sub.2HfBr.sub.6 single crystals (table S5).

    [0197] To deconvolve the emission from (18C6@K).sub.2ZrBr.sub.6 impurities, a two-peak Gaussian fitting was applied to the PL spectrum at each temperature. FIG. 50 shows an example at 4 K. The FWHMs of the (18C6@K).sub.2HfBr.sub.6 peaks were obtained from the Gaussian fittings and are summarized in table S6. The temperature dependence of the FWHM of the emission peak was modeled using the theory of Toyozawa, which applies a configuration coordinate model to explain the broadening of the emission originating from electron-phonon coupling. The FWHM depends on the Boltzmann constant kB, the effective phonon energy E.sub.ph, the temperature T, and the Huang-Rhys electron phonon coupling parameter S

    [00001] FWHM = 2 . 3 6 S E ph coth E p h 2 K B T ( Equation 1 )

    [0198] The relation between FWHM and temperature is shown in FIG. 26B. Analyzing the data according to Eq. 1 yielded a coupling factor S.sub.1=92.23.6 and an effective phonon energy E.sub.ph1=21.40.5 meV. This phonon mode corresponded to the asymmetric stretching mode (E.sub.g) of the [HfBr.sub.6].sup.2 octahedra, which was observed at 20.4 meV (164.5 cm.sup.1) in the Raman spectrum (FIG. 51). However, this phonon mode was only responsible for STE formation up to 190 K. For temperatures >190 K, a higher energy phonon mode dominated STE formation.

    [0199] Shifting the zero temperature of Eq. 1 by 190 K, a second fit could be obtained with a coupling factor S2=108.812.4 and an effective phonon energy Eph2=25.81.6 meV. This phonon mode corresponded to the symmetric stretching mode (A.sub.1g) of the [HfBr.sub.6].sup.2 octahedra at 25.1 meV (202.5 cm.sup.1). The large Huang-Rhys factor S in both scenarios indicated a very strong electron-phonon coupling in this material. For example, S for CsPbX.sub.3 (where X=Br.sup. or I.sup.) is <1, and the S for double perovskite Cs.sub.2AgBiBr.sub.6 is only 12 (48). STE behavior is closely related to the octahedra packing dimensionality. Through the supramolecular approach provided herein, the [HfBr.sub.6].sup.2 octahedra were more isolated by the bulky (18C6@K).sup.+ complexes, which led to stronger self-trapping with larger S values.

    [0200] Excitation wavelength-dependent PL mapping of (18C6@K).sub.2HfBr.sub.6 (FIG. 26C) showed that for excitation wavelengths <285 nm, a broad PL peak at 445 nm emerged. The PL peak position and shape were independent of the excitation wavelength <285 nm. Thus, for above and gap excitation, the emission originated from the relaxation of the same excited state. However, for excitation wavelengths >285 nm, a much weaker PL peak at 550 nm replaced the previous PL peak that arose from the 0.6 at % (18C6@K).sub.2ZrBr.sub.6 impurity, and 2D PLE mapping of (18C6@K).sub.2ZrBr.sub.6 showed a single PL peak at 550 nm from 245-nm to 330-nm excitation (FIG. 52).

    [0201] Time-resolved PL (TRPL) studies on the supramolecular assembled single crystals revealed that the PL decay of the (18C6@K).sub.2ZrBr.sub.6 could be mostly described by a monoexponential decay profile on the microsecond timescale, with a PL lifetime of 6.80 ms (FIG. 26D and Table 16). By contrast, Cs.sub.2ZrBr.sub.6 bulk crystal featured a triple-exponential PL decay, yielding decay time constants of 40 ns (8.9%), 0.99 ms (24%), and 4.6 ms (68%). Additionally, Cs.sub.2ZrBr.sub.6 nanocrystals showed a double-exponential PL decay with time constants at 0.78 and 4.5 ms. The PLQY was related to both the radiative and nonradiative decay rates [PLQY=k.sub.rad/(k.sub.rad+k.sub.nonrad)], so a more sluggish radiative decay did not necessarily correlate to a lower PLQY. Notably, the PLQY of (18C6@K).sub.2ZrBr.sub.6 powders (49.8%) was greater than that of K.sub.2ZrBr.sub.6 powders (46.3%, from measurement provided herein) and Cs.sub.2ZrBr.sub.6 nanocrystals [44%]. This observation suggested that the nonradiative decay rate of the supramolecular sample was slower than that of the vacancy-ordered double perovskite phases and may indicate a lower defect density in the assembled crystals provided herein. The PL decay of the (18C6@K).sub.2ZrCl.sub.4Br.sub.2 single crystal could also be fit with a single exponential function with an even longer PL lifetime (12.08 ms) (FIG. 26D and Table 17). Cs.sub.2ZrCl.sub.6 had a slightly longer PL lifetime (7.5 ms) compared with that of Cs.sub.2ZrBr.sub.6. This result suggested that the supramolecular material system had a longer PL lifetime and slower nonradiative decay rate.

    [0202] The photostability of these highly emissive blue and green emitters was evaluated. Notably, previous research in the organic light emitting diode (OLED) community has used a xenon lamp to simulate solar irradiation, dissolving Ir complexes in deuterated toluene for reference measurements of green and blue emission (51, 52). To ensure a fair comparison, identical irradiation energy density (62 mW/cm.sup.2) and temperature (35 C.) were applied, and deuterated toluene was used to disperse the (18C6@K).sub.2HfBr.sub.6 and (18C6@K).sub.2ZrCl4Br2 powders. FIG. 53 shows the PL intensity decay of the (18C6@K).sub.2HfBr.sub.6 and (18C6@K).sub.2ZrCl.sub.4Br.sub.2 samples under continuous irradiation. Both decay trends could be accurately described by the integrated rate law for the first-order reaction [1n(I.sub.t/I.sub.0)=kt]. The rate constants of photodegradation were estimated to be 5.110.sup.3 h.sup.1 and 3.010.sup.3 h.sup.1 for (18C6@K).sub.2HfBr.sub.6 and (18C6@K).sub.2ZrCl.sub.4Br.sub.2, respectively. Notably, even under stringent irradiation conditions, the PL intensities of (18C6@K).sub.2HfBr.sub.6 and (18C6@K).sub.2ZrCl.sub.4Br.sub.2 decreased to 80% after 43 and 73 hours, respectively. These findings underscore the superior photostability of the supramolecular assembled samples compared with most Ir complexes, rivaling the best reported green-emitting fac-[Ir(ppy).sub.3] reference (k=2.610.sup.3 h.sup.1) (51, 52). Previous studies on the photodegradation of the Ir complexes, such as Ir(ppy).sub.3 and Ir(piq).sub.3, have identified singlet oxygen attack and interaction of the excited-state molecule with its local environment as primary degradation pathways.

    Blue-Green Dual-Color Display and 3D Printing

    [0203] The high PLQY of the blue and green emission colors in the powders were preserved in thin films, which would enable various optoelectronic device applications (54-56). Because the powders were stable in nonpolar organic solvents, they could be evenly dispersed into solution to form inks. DCM was used because its low boiling point (39.6 C.) leads to high volatility for drying films, and PS was added to create inks suitable for drop casting or spin coating by increasing the viscosity (FIG. 27A). The image of (18C6@K).sub.2HfBr.sub.6/PS ink under a white lamp (FIG. 27B) shows that a uniform white suspension was achieved that exhibited a bright blue emission under 254-nm excitation. The emission was solely from the (18C6@K).sub.2HfBr.sub.6 powders in the ink because the shape of the PL spectrum was the same as the PL shape of the powders (FIG. 54). The solution PLQY was 90.8% (FIGS. 27B and 55), which was only 5.5% less than the powder PLQY. This reduction was expected because DCM and PS do not absorb strongly in the blue color wavelength region (FIG. 56), and the suspended powders in the ink could cause losses through scattering. The (18C6@K).sub.2ZrCl.sub.4Br.sub.2/PS ink also preserved the green emission of the (18C6@K).sub.2ZrCl.sub.4Br.sub.2 powders with a solution PLQY of 75.0% (FIGS. 27C and 57).

    [0204] The inks could be drop casted under ambient conditions, and, after rapid solvent evaporation, a uniform thin film forms (FIGS. 27A, 27D, and 27E). PXRD patterns of the (18C6@K).sub.2HfBr.sub.6/PS composite (FIG. 58) and the (18C6@K).sub.2ZrCl.sub.4Br.sub.2/PS composite (FIG. 59) showed that the structural integrity of the powders was preserved in the PS matrix. Scanning electron microscopy (SEM) imaging of the (18C6@K).sub.2HfBr.sub.6 powders and the (18C6@K).sub.2HfBr.sub.6/PS composite thin-film surface (FIG. 60) indicated that the submicrometer-sized powders were uniformly dispersed. Cross sectional SEM imaging of the thin film (FIGS. 61A-61D) proved the presence and uniformity of the powders across the thin film. Under UV irradiation, (18C6@K).sub.2HfBr.sub.6/PS and (18C6@K).sub.2ZrCl.sub.4Br.sub.2/PS composite thin films showed bright blue and green emissions, respectively (FIGS. 27D and 27E). The shapes of the PL spectra of the thin films were the same as those for the powders (FIGS. 53 and 62), and the PLQYs were 80.3% (FIG. 63) and 69.0% (FIG. 64) for blue- and green emitting composites, respectively.

    [0205] The stability of the air-sensitive Hf and Zr octahedral clusters was further enhanced in the PS polymer composite. Both Cs.sub.2HfBr.sub.6 and Cs.sub.2ZrBr.sub.6 double-perovskite structures are predicted to be thermodynamically unstable in the presence of water and oxygen, and K.sub.2HfBr.sub.6 and K.sub.2ZrBr.sub.6 powders turn from a white to a brownish color after a few minutes of air exposure and became non-emissive. By contrast, the (18C6@K).sub.2HfBr.sub.6/PS and (18C6@K).sub.2ZrCl.sub.4Br.sub.2/PS composites maintained their blue and green emission colors, respectively, after 1 month of storage in the air (FIG. 65). The air-stable PS polymers along with the hydrophobic crown ethers could greatly protect the air-sensitive Hf and Zr metal emission centers.

    [0206] Display applications of the powder-PS composite thin films were explored. A digital mirror device with a pixel resolution of 2560 by 1440 sequentially patterned 250-nm UV light through projection optics onto the (18C6@K).sub.2HfBr.sub.6/PS composite thin film with a spot size of 6.9 by 3.9 mm at a frame rate of 60 Hz (schematic of the process is illustrated in FIG. 27A). An emissive blue Cal logo was illuminated on the thin film with dimensions 3.8 mm in height and 4.7 mm in width (FIG. 27F). The logo exhibited high luminosity characterized by sharply defined edges. To further demonstrate dynamically changing display luminescence, the alphabet sequence (from A to Z) was illuminated onto the thin film with a fast flipping rate (0.1 s per letter). A video of 2.6 s was recorded. Although the duration of each letter was very short, the blue emission with the shape of the letters was sharp and bright, as illustrated in the snapshot photos (FIG. 27G). The size of the letters was only 3.1 mm in width and 3.9 mm in length, but every feature of the letters was clearly visible with similar emission intensity owing to the high uniformity of the thin film. Furthermore, the response time of the display should be fast because the PL decay rate of the (18C6@K).sub.2HfBr.sub.6 powders was 3 orders of magnitude faster than the frame rate of the digital mirror device. The letters switch extremely fast, with no blurring, ghosting, or trailing effects.

    [0207] These emissive powders could also be processed with high-resolution 3D printing technologies after blending them uniformly into a monomer resin. Conventional resins for 3D printing typically use dyes as the photoabsorber to control the depth of UV penetration and, consequently, the printing resolution. However, dyes absorb light and color the final printed parts. To avoid interference with the blue and green emitters provided herein, a photoabsorber free resin mainly composed of photomonomer poly(ethylene glycol) diacrylate (PEGDA) was used but with a high content of photoinhibitor to control the printing resolution. The polymerized PEGDA resin exhibited minimal absorption within the visible spectrum, featuring a modest absorption peak from 355 to 425 nm (FIG. 66A). Also, under 250-nm UV excitation, the resin exhibited substantially low emission intensity (FIG. 66B). Hence, the emission colors in the blue and green range of the emitters provided herein remained largely unaffected.

    [0208] Upon stirring and sonication, the powders were uniformly dispersed into the PEGDA resin. Multimaterial digital light-printing method was used to achieve a 3D assembly of the blue and green emitters into complex macro and microarchitectures. Under 405-nm structured UV light illumination, the resin rapidly converted into solid 3D structures (FIG. 28A). The PL spectra from the (18C6@K).sub.2HfBr.sub.6/PEGDA and the (18C6@K).sub.2ZrCl.sub.4Br.sub.2/PEGDA composites were similar to those of the powders (FIGS. 66C, 66D, 67, and 68). The printed architectural models of the Eiffel Tower (FIG. 28B), after excitation at 254 nm, showed their respective blue and green colors (FIG. 28C). The dimensions of the two Eiffel Towers were within a few centimeters, with high-resolution spatial features (FIG. 28A). The submicrometer scale of these powders and a printing layer thickness of 40 mm enabled even distribution throughout each layer and ensured a homogeneous emission color profile across the entire architectural construct.

    [0209] A single 3D-printed structure could also manifest emissions in both blue and green by alternative resins during the printing procedure. An Eiffel Tower design characterized by blue emissions at its upper and lower segments with green emissions in its central region is shown in FIG. 28D, and a second-order hierarchical lattice structure (octet truss) was realized with one half radiating in blue and the other in green (FIG. 28E). Notably, a close-up view of the boundary between these blue- and green emitting regions within the octet truss structure revealed the high precision in color transition without any color crossover on either side. Twisted (FIGS. 28F and 69) and conformal (FIGS. 28G and 70) octet truss architectures with dual emissions were also achieved with bright emissions and high structural accuracy. Other complex topologies, such as cuboctahedron, tetrakaidecahedron, octet truss, and Menger sponge with the blue emitter embedded (FIGS. 28H, 71, and 72), were also obtained to exhibit the variety of structures that could be printed with the light emitting ink. These demonstrations served as a proof of concept for integrating emissive ionic powders with 3D printing technology. The potential applications of 3D-printed light emitting structures are extensive and constantly evolving, ranging from intricate interior ambient-lighting solutions to seamless integration into wearable devices.

    SUMMARY

    [0210] A supramolecular assembly strategy was demonstrated for achieving halide perovskite blue and green emitters with ultrahigh PLQYs. Specifically, (18C6@K).sub.2HfBr.sub.6 warranted a blue emission with a near-unity (96.2%) PLQY, and (18C6@K).sub.2ZrCl4Br.sub.2 showed a green emission with a PLQY of 82.7%. The emission of the supramolecular assembled samples originated from the STE emission, with strong electron phonon coupling and microsecond PL lifetimes. The supramolecular approach is very promising for solution processability. The (18C6@K).sub.2HfBr.sub.6/PS-DCM ink maintained a high PLQY of >90%. Uniform thin films were fabricated from this ink through a drop-casting technique. The (18C6@K).sub.2HfBr.sub.6/PS composite had blue emission with a PLQY of >80%, making it favorable for patterning, display, and printing applications. The powders with blue and green emissions were also highly compatible with the 3D printing technology. The supramolecular assembly approach for halide perovskite building block catalyzes further investigation into the synthesis and characterization of supramolecular assembled functional materials, laying the foundation for substantial progress in the field.

    Materials and Methods

    [0211] Chemicals. 18-crown-6 (18C6, 99%, Sigma Aldrich), KBr (99%, Sigma Aldrich), HfBr.sub.4 (anhydrous, 98% (99.7%-Hf), Strem Chemicals), ZrBr.sub.4 (99%, Alfa Aesar), acetonitrile (ACN, Fisher Chemical), diethyl ether (DEE, Sigma Aldrich), dichloromethane (DCM, Fisher Chemical), polystyrene (PS, average Mw192000, Sigma Aldrich), toluene-d8 (99%, Sigma Aldrich), photo monomer poly(ethylene glycol) diacrylate (PEGDA, Mn 250, Millipore Sigma), photo initiator phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (Millipore Sigma), and inhibitor 4-methoxyphenol (Millipore Sigma) were used as received without further purification or modification. 18C6, KBr, HfBr.sub.4, and ZrBr.sub.4 were stored in an argon glovebox with O.sub.2 and H.sub.2O level below 0.5 ppm.

    [0212] Synthesis of K.sub.2HfBr.sub.6 and K.sub.2ZrBr.sub.6 powders. KBr and HfBr.sub.4 or ZrBr.sub.4 precursors with molar ratio 1:2 were measured and mixed into a grinder in an argon glovebox. The precursors were vigorously grinded for 10 minutes and then transferred into a 20 ml glass vial. They were heated on a hot plate in the glovebox at 200 C. for 1 h. The powder mixture was grinded again for 10 minutes, and then heated for another 1 h at 200 C. The grinding and heating procedure were repeated for five times until all the KBr had reacted with HfBr.sub.4 or ZrBr.sub.4 according to inert atmosphere x-ray diffraction. Then the powder mixture was heated at 500 C. for 10 minutes to evaporate all the surplus HfBr.sub.4 or ZrBr.sub.4 precursors.

    [0213] Synthesis of (18C6@K).sub.2HfBr.sub.6 and (18C6@K).sub.2ZrBr.sub.6 powders and single crystals. 18C6, KBr, and HfBr.sub.4 or ZrBr.sub.4 precursors with molar ratio 2:2:1 were weighed in the glovebox and transferred out into atmosphere using a 20 ml glass vial. The precursors were completely dissolved under 80 C. with vigorous stirring in ACN within 30 minutes. To obtain (18C6@K).sub.2HfBr.sub.6 and (18C6@K).sub.2ZrBr.sub.6 powders, 10 ml precursor solution was added into 30 ml DEE in a 50 ml centrifuge tube. White powders immediately formed upon the mixture of the two solutions. The powders were separated using centrifugation. The centrifugation speed was 5000 rpm, and the duration was 5 minutes. The powders were washed with DEE for three times and dried in vacuum at room temperature overnight. (18C6@K).sub.2HfBr.sub.6 and (18C6@K).sub.2ZrBr.sub.6 single crystals were grown using an anti-solvent diffusion method. 1 ml of the abovementioned precursor solution was added into a 4 ml vial, which was placed into a 20 ml vial with 4 ml of DEE. After approximately two days, single crystals were formed on the bottom and the wall of the 4 ml vial. Single crystals were washed 3 times with DEE and dried in vacuum at room temperature overnight. Powders and single crystals were stored in an argon glovebox with O.sub.2 and H.sub.2O level below 0.5 ppm for future use.

    [0214] Synthesis of (18C6@K).sub.2ZrClxBr.sub.6-x powders and single crystals. 18C6, KCl, KBr, ZrCl4 and ZrBr.sub.4 precursors with molar ratio 12:2x:122x:x:6x were weighed in the glovebox and transferred out into atmosphere using a 20 ml glass vial. The precursors were completely dissolved under 80 C. with vigorous stirring in ACN within 30 minutes. To obtain (18C6@K).sub.2ZrCl.sub.6-xBr.sub.x powders, 10 ml precursor solution was added into 30 ml DEE in a 50 ml centrifuge tube. White powders immediately formed upon the mixture of the two solutions. The powders were separated using centrifugation. The centrifugation speed was 5000 rpm, and the duration was 5 minutes. The powders were washed with DEE for three times and dried in vacuum at room temperature overnight. (18C6@K).sub.2ZrCl.sub.4Br.sub.2 single crystal was grown 3 using an anti-solvent diffusion method. 1 ml of the abovementioned precursor solution was added into a 4 ml vial, which was placed into a 20 ml vial with 4 ml of DEE. After approximately two days, single crystals were formed on the bottom and the wall of the 4 ml vial. Single crystals were washed 3 times with DEE and dried in vacuum at room temperature overnight. Powders and single crystals were stored in an argon glovebox with O.sub.2 and H.sub.2O level below 0.5 ppm for future use.

    [0215] Synthesis of (18C6@K).sub.2HfBr.sub.6/PS in DCM and (18C6@K).sub.2ZrCl.sub.4Br.sub.2/PS in DCM inks. 100 mg PS was fully dissolved in 5 ml DCM with a stir bar in a 20 ml vial at room temperature. 50 mg (18C6@K).sub.2HfBr.sub.6 or (18C6@K).sub.2ZrCl.sub.4Br.sub.2 powders were added into the abovementioned PS/DCM solution, then alternatively stirred and sonicated for 4 hours at room temperature to achieve a uniform suspension. The inks for PLQY measurements were diluted with DCM to achieve a 0.3 absorbance to guarantee an accurate solution PLQY determination.

    [0216] Synthesis of (18C6@K).sub.2HfBr.sub.6/PS and (18C6@K).sub.2ZrCl.sub.4Br.sub.2/PS composite thin films. The composite thin films were synthesized from direct drying of the inks in a glass petri dish at room temperature in the air. The dried thin films were then peeled off from the petri dish and cut into a round shape.

    [0217] Scanning electron microscopy (SEM) with standard secondary electron imaging. Prior to imaging, the thin film samples were sputtered with 5 nm of Au (Denton Vacuum, Moorestown, NJ). The samples were imaged at 15 kV/high probe current by Benchtop SEM (JCM-7000, Tokyo, Japan).

    [0218] Scanning electron microscopy with energy dispersive x-ray (SEM/EDX) spectroscopy. Prior to imaging, the single crystal samples were sputtered with 5 nm of Au (Denton Vacuum, Moorestown, NJ). A field-emission SEM (FEI Quanta 3D FEG SEM/FIB) and the EDX detector were used to determine elemental ratios at the QB3-Berkeley Biomolecular Nanotechnology Center (BNC).

    [0219] Inductively coupled plasma atomic emission spectroscopy (ICP-AES). ICP-AES results were collected using a Perkin Elmer ICP Optima 7000 DV Spectrometer at the Microanalytical Facility in College of Chemistry, UC Berkeley.

    [0220] Single-crystal x-ray diffraction (SCXRD). The SCXRD data were collected at the Small Molecule X-ray Crystallography Facility (CheXray) in College of Chemistry, UC Berkeley. SCXRD were measured with a Rigaku XtaLAB P200 instrument equipped with a MicroMax-007 HF microfocus rotating anode and a Pilatus 200K hybrid pixel array detector using monochromated Cu K radiation (=1.54184 A) or Mo K radiation (=0.71073 A). All crystal datasets were collected at room temperature (298 K). CrysAlisPro (61) was used for data collection and data processing, including a multi-scan absorption correction applied using the SCALE3 ABSPACK scaling algorithm within CrysAlisPro. Using Olex2 (62), the structures were solved with the SHELXT (63) structure solution program using Intrinsic Phasing and refined with the SHELXL (64) refinement package using Least Squares minimization. Due to the occupation of disordered solvent molecules in the crystal voids, solvent masks were used during the refinement. All reflections where [error/esd]>5 4 were omitted, as the existence of disordered molecules will result in high error/esd values in low d-spacing diffractions.

    [0221] Ambient condition powder x-ray diffraction (PXRD). PXRD data of (18C6@K).sub.2HfBr.sub.6 powders, (18C6@K).sub.2ZrBr.sub.6 powders, (18C6@K).sub.2HfBr.sub.6/PS composite, and (18C6@K).sub.2ZrCl.sub.4Br.sub.2/PS composite were collected using a Bruker D8 laboratory diffractometer with a Cu K radiation source in ambient condition.

    [0222] Inert atmosphere PXRD. PXRD of K2HfBr.sub.6 and K.sub.2ZrBr.sub.6 powders were collected using a Rigaku Miniflex 6G Benchtop Powder XRD with a Cu K radiation source and an inert atmosphere sample holder. The powder samples were loaded onto the sample holder inside an argon glovebox with O.sub.2 and H.sub.2O level below 0.5 ppm.

    [0223] Raman spectroscopy. The Raman spectra of all the samples were measured by a confocal Raman microscope system (Horiba LabRAM HR800 Evolution). The powders were dispersed onto glass microscope slides for measurement. A continuous-wave (cw) 632.8-nm laser was focused onto a crystal facet at a constant power density set by neutral density filters. The Raman signal from the sample was collected using a microscope objective in a backscattering geometry (100, NA 0.6). High-resolution Raman spectra were measured with a charge-coupled device (CCD) detector equipped with a diffraction grating of 1800 gr/mm and a long pass filter (100 cm.sup.1) to remove the Rayleigh scattering line from the signal.

    [0224] Photoluminescence spectroscopy (PL) and photoluminescence quantum yield (PLQY). PL and PLQY measurements were collected with the FS5 Spectrofluorometer (Edinburgh Instruments) using the SC-30 integrating sphere. The powders were densely packed onto the sample holder and then the surface was flattened for measurement. A 150 W continuous-wave ozone-free xenon lamp was focused onto the sample. (18C6@K)2HfBr6 and K2HfBr.sub.6 were excited at 275-nm excitation wavelength. (18C6@K).sub.2ZrBr.sub.6 and K.sub.2ZrBr.sub.6 were excited at 290-nm excitation wavelength. (18C6@K).sub.2ZrCl.sub.3Br.sub.3, (18C6@K).sub.2ZrCl.sub.4Br.sub.2, and (18C6@K).sub.2ZrCl.sub.4.5Br.sub.1.5 were excited at 295-nm excitation wavelength. The PL signal from the sample was collected by a UV-enhanced Si photodiode array equipped with a diffraction grating of 1200 gr/mm. The PLQY values were determined by the PLQY determination wizard of the Fluoracle (version 2.15.2) operating software for the FS5 Spectrofluorometer. PL and PLQY measurements of the PS polymer composite samples were measured with the free-standing composite films. PL and PLQY measurements of the DCM ink samples were measured using a quartz cuvette as the sample holder.

    [0225] Low-temperature photoluminescence spectroscopy (Low-T PL). The low-T PL measurements were collected with a home-built PL microscope system. Powder samples were dispersed onto mica substrates for measurement. A broadband deuterium lamp (Thorlabs SLS204 Stabilized Deuterium Lamp) was filtered down to a 250 nm excitation line using a bandpass filter (250 nm/10 nm). The 250 nm excitation line was focused obliquely onto the sample with a constant power density. The PL signal from the sample was collected using a microscope objective (50) coupled to a long pass filter (cut-on wavelength: 325 nm) to remove the excitation line from the signal. PL spectra were collected with a Si charge-coupled device 5 (CCD) detector cooled to 120 C. via liquid nitrogen and equipped with a diffraction grating of 150 gr/mm. The low-T (4 K to 293 K) PL measurements were performed in a Janis ST-500 SuperTran continuous flow cryostat system attached to the home-built PL microscope system. Liquid gallium-indium eutectic (Ga 75.5%/In 24.5%, 99.99% trace metals basis) was used to adhere samples to the cryostat stage, and the cryostat chamber was placed under vacuum with a continuous flow of liquid helium (LHe). A temperature controller as used to monitor the cryostat stage temperature and maintain it at the desired temperature.

    [0226] Photoluminescence excitation spectroscopy (PLE). PLE measurements were collected with the FS5 Spectrofluorometer (Edinburgh Instruments) using the SC-30 integrating sphere. Powders were densely packed onto the sample holder and then the surface was flattened for measurement. A 150 W continuous-wave ozone-free xenon lamp created a wide range of excitation wavelengths that were focused onto the sample.

    [0227] Chromaticity determination. The CIE 1931 chromaticity diagrams for all the samples were determined using the Fluoracle (version 2.15.2) operating software for the FS5 Spectrofluorometer from the corresponding PL spectra.

    [0228] UV-visible (UV-vis) absorption spectroscopy. The absorption spectra for all the samples were measured by a UV-vis spectrophotometer (Shimadzu UV-2600). Data was collected in absorption mode over a wavelength range of 200 nm and 900 nm with a medium scanning rate.

    [0229] Time-resolved photoluminescence spectroscopy (TRPL). Single crystals were placed and pressed onto a double-sided copper tape supported by a quartz slide. The (18C6@K).sub.2ZrCl.sub.4Br.sub.2 single crystal sample was excited at 310 nm, and the (18C6@K).sub.2ZrBr.sub.6 single crystal sample was excited at 330 nm. The rep. rate of the excitations was 7.6 kHz (135 s between pulses. 250 fs pulse) and the PL was separated from the residual excitations using two color glass filters (CS #: 3-70). A photomultiplier tube (PMT) (Hamamatsu-R9110) biased at 2 kV was used as the detector. The PMT output was read using a 300 MHz oscilloscope, each trace was averaged 512 times.

    [0230] Photodegradation tests. (18C6@K).sub.2HfBr.sub.6 and (18C6@K).sub.2ZrCl.sub.4Br.sub.2 powders were dispersed in toluene-d8 in an argon glovebox with O.sub.2 and H.sub.2O level below 0.5 ppm, and 3 ml of the suspension was transferred into a UV quartz cuvette with a septum screw cap. Parafilm was wrapped around the cuvette cap to create a tight seal. A stir bar was placed inside the cuvette to stir the suspension during the entire irradiation. The suspensions were irradiated with a simulated solar irradiation at 62 mW/cm.sup.2 and 35 C. The light source used was a 300 W xenon lamp calibrated with a thermopile (MKS Newport 919P-040-50) to make sure 62 mW/cm2 were delivered to the suspensions. The suspensions were placed on a hot plate at 35 C. and under stirring of 1000 rpm. The PL spectra of the samples were measured with the FS5 Spectrofluorometer (Edinburgh Instruments) using the SC-30 integrating sphere. The PL spectra of the (18C6@K).sub.2HfBr.sub.6 sample were measured at 275-nm excitation under constant excitation power. The PL spectra of the (18C6@K).sub.2ZrCl.sub.4Br.sub.2 sample were measured at 295-nm excitation under constant excitation power.

    [0231] 2D display on thin film. (18C6@K).sub.2HfBr.sub.6/PS thin film was illuminated at a 250-nm wavelength (high-power UV LED with ball lens, 250 nm, LED250J, Thorlabs) through structured UV light using a digital light modulator (digital mirror device, pixel resolution 25601440). The structured UV light with programmed digital patterns was sequentially patterned through projection optics onto the thin film at a spot size of 6.9 by 3.9 mm at a frame rate of 60 Hz. The thin film instantly displayed patterned images which were recorded through a digital camera.

    [0232] Printing of light emitting 3D micro-architectures. A photo-absorber-free resin comprised of photo monomer PEGDA, photo initiator phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (0.5 wt. % of PEGDA), and inhibitor 4-methoxyphenol (1.2 wt. % of PEGDA) was applied. (18C6@K).sub.2HfBr.sub.6 and (18C6@K).sub.2ZrCl.sub.4Br.sub.2 powders were blended into the photo-absorber-free resin in a 5 mg/g ratio using vortex and bath sonication for 15 min. The inhibitor in high content is required to control the UV penetration depth and ensure the printing resolutions in the absence of photo absorbers. Upon 405-nm UV exposure (light intensity 7 mW/cm.sup.2), the photo-absorber-free resin was rapidly converted into solid 3D structures.

    [0233] Density functional theory (DFT) calculations. The electronic band structures of (18C6@K).sub.2HfBr.sub.6, K.sub.2HfBr.sub.6, (18C6@K).sub.2ZrBr.sub.6, and K.sub.2ZrBr.sub.6 were calculated by DFT calculations with the CASTEP (65) code implemented in the Materials Studio 2020. The norm conserving pseudopotential (66) was applied for electron interactions in metal halides. All three structures models were imported from CIF files, and the geometry optimization has been applied with PBEGGA (67). A fine frame was chosen for energy cutoffs and calculation quality. Electronic band structures and partial density of states (pDOS) were calculated with PBE+GGA without spin-orbital coupling (SOC).

    Example 3: Supramolecular Assembly of Halide Perovskites Having a 1D Chain Structure

    Supramolecular Assembled Manganese Halide Green Emitter with Over 80% PLQY and Narrow FWHM

    [0234] Green emitters play a pivotal role in modern display technologies. Displays harness a blend of red, green, and blue (RGB) emitting materials to achieve the rich spectrum of colors in each pixel. For instance, in quantum dot LED (QLED) displays, a blue light serves as the emitting source, with quantum dots converting this light into both red and green hues (FIG. 73). In identifying the optimal green light-emitting materials, several key criteria are very important: (1) a high photoluminescence quantum yield (PLQY) ensures high brightness and energy efficiency; (2) a narrow full width at half maximum (FWHM) fosters color purity, facilitating the vivid and precise hues; and (3) the material must be readily excitable by blue light, ensuring seamless integration within the display structure.

    [0235] Crown ether-assisted supramolecular assembly approach provided herein can enable a facile solution-based synthesis of a new green emitter that satisfies all the abovementioned criteria. [MnBr.sub.4].sup.2 complexes are assembled into a new (18C6@Ba)MnBr.sub.4 crystal structure. For the synthesis, a clear precursor solution was obtained with acetonitrile (ACN) at 80 C. with the concentration of 10 mM for 18C6, BaBr.sub.2 and MnBr.sub.2. (18C6@Ba)MnBr.sub.4 powders and single crystals were grown using the similar diethyl ether-assisted anti-solvent crystallization method as before. The crystal structure of (18C6@Ba)MnBr.sub.4 was determined from single-crystal x-ray diffraction (SCXRD). (18C6@Ba)MnBr.sub.4 crystallized in the R3 space group with lattice parameters of a=14.2087 and c=9.8911 (FIGS. 74A-74D, Table 20).

    [0236] In the crystal structure, the [MnBr.sub.4].sup.2 complexes and the (18C6@Ba).sup.2+ complexes are alternatingly connected into a linear chain, and the chains then packed into a hexagonal crystal structure. One side of the Ba atom is coordinated with one Br atom, and the other side is coordinated with three Br atoms. This configuration enables the strong structural stability of the [MnBr.sub.4].sup.2 complexes, as demonstrated by the near perfect tetrahedral shape of the [MnBr.sub.4].sup.2 complexes. This has great implications on the emission color of the [MnBr.sub.4].sup.2 complexes.

    [0237] Detailed optical property measurement of this new material was conducted. (18C6@Ba)MnBr.sub.4 has a green emission centered at 513 nm. The emission intensity is very strong, and the PLQY is 82.1%. Due to the high stability of the [MnBr.sub.4].sup.2 complexes in the crystal structure, it has a very narrow emission peak (FWHM=0.17 eV) (FIG. 75A). The PL spectrum and the PLQY value showed in FIG. 75A is measured using 365 nm and 449 nm excitation, respectively. FIG. 75B shows the emission color of (18C6@Ba)MnBr.sub.4 on the CIE 1931 chromaticity diagram. The color is close to the boundary of the diagram, meaning the purity of the green color is high. Furthermore, the green emitter can be readily excited by blue light. The photoluminescence excitation (PLE) spectrum shows that blue light from 425 nm to 475 nm can excite the material. FIG. 75C illustrates the 2D PLE of (18C6@Ba)MnBr.sub.4. It further confirms that both UV and blue light can excite the material, and the PL peaks generated from both excitations remain the same (centered at 513 nm).

    [0238] The (18C6@A)MX.sub.4 (A.sup.2+=alkaline earth metal cation, M.sup.2+=transition metal cation, X.sup.=halide anion) crystal structure can be expanded to a variety of compositions. The X site can be tuned from Br to Cl (Tables 19, 20), and the M site can be changed from Mn to Ni (Tables 19, 21).

    Expansion of the 1D Chain Structure

    [0239] Expanding along the crown ether/metal halide complex alternating 1D chain structure, a novel structure that also encompasses the 5-halide-coordinated metal halide complex: (18C6@Ba)SbCl.sub.5 has been discovered. The synthetic method of this new compound is very similar to (18C6@Ba)MnBr.sub.4. ACN is applied as the solvent to dissolve a stoichiometric ratio amount of 18C6, BaCl.sub.2, and SbCl.sub.3 precursors, and DEE is used as the anti-solvent. Upon crystallization, [SbCl.sub.5].sup.2 complexes are assembled into a similar linear chain structure facilitated by (18C6@Ba).sup.2+ (FIGS. 76A, 76B). The Ba.sup.2+ in the crown ether is disordered. Half of the cation is located above the crown ether, while the other half is below the crown ether, and the crown ether is the mirror plane for the two parts. The [SbCl.sub.5].sup.2 complexes are also disordered, and the 5 Cl atoms occupy 6 octahedral coordination sites of the Sb atom, each with 5/6 possibility. The alternating linear chains are then assembled into a rhombohedral crystal structure with R-3 space group. This high symmetry space group guarantees the linearity of the 1D chains (FIGS. 76C, 76D, Table 21).

    [0240] The expansion of the composition leads to the discovery of more emission colors. (18C6@Ba)SbCl.sub.5 has a strong orange emission at 639 nm using 375-nm excitation (FIG. 76E). Under confocal microscope, the belt-shape (18C6@Ba)SbCl.sub.5 single crystal is transparent under white light, and it has a uniform orange emission under 375-nm excitation. This result demonstrates that a family of new materials can be achieved, and the crown ether/metal halide complex linear chain structure have rich optical properties.

    TABLE-US-00020 TABLE 20 Crystallographic tables for (18C6@Ba)MnBr.sub.4 and (18C6@Ba)MnCl.sub.4 Crystal (18C6@Ba)MnBr.sub.4 (18C6@Ba)MnCl.sub.4 ICSD Number 2363488 2363487 Empirical formula C12H24BaBr4MnO6 C12H24BaC14MnO6 Formula weight 776.20 598.39 Temperature/K. 100 100 Crystal system trigonal trigonal Space group R3 R3 a/ 14.0618(2) 13.9014(8) b/ 14.0618(2) 13.9014(8) c/ 9.8513(1) 9.4665(5) / 90 90 / 90 90 / 120 120 Volume/.sup.3 1686.964800 1584.3(2) Z 3 3 p.sub.calcmg/mm.sup.3 2.292 1.882 /mm.sup.1 26.625 2.979 F(000) 1095 879 Crystal size/mm.sup.3 0.14 0.13 0.12 0.142 0.124 0.103 Radiation Cu K ( = 1.54184 ) Cu K ( = 1.54184 ) 2 range for data 5.7380 to 77.9410 3.9670 to 30.0570 collection Index ranges 17 h 16, 16 h 19, 17 k 17, 18 k 19, 12 l 12 12 l 12 Reflections 12094 4213 collected Independent 1602[R(int) = 0.0457] 1664[R(int) = 0.0348] reflections Data/restraints/ 1602/1/74 1664/1/74 parameters Goodness-of-fit 1.061 0.499 on F.sup.2 Final R indexes R.sub.1 = 0.0191, R.sub.1 = 0.0203, [ I >= 2 (I)] wR.sub.2 = 0.0512 wR.sub.2 = 0.0572 Final R indexes R.sub.1 = 0.0191, R.sub.1 = 0.0204, [all data] wR.sub.2 = 0.0512 wR.sub.2 = 0.0576 Largest diff. 0.439/4.95 0.518/0.500 peak/hole/e .sup.3

    TABLE-US-00021 TABLE 21 Crystallographic tables for (18C6@Ba)NiBr.sub.4 and (18C6@Ba)SbCl.sub.5 Crystal (18C6@Ba)NiBr.sub.4 (18C6@Ba)SbCl.sub.5 ICSD Number 2363409 2363486 Empirical formula C12H22BaBr4NiO6 C1206BaSbC15 Formula weight 777.939 700.670 Temperature/K. 100 100 Crystal system trigonal trigonal Space group P3 R-3 a/ 14.1069(8) 13.721(4) b/ 14.1069(8) 13.721(4) c/ 9.6236(8) 10.276(5) / 90 90 / 90 90 / 120 120 Volume/.sup.3 1658.56(19) 1675.4(11) Z 3 3 p.sub.calcmg/mm.sup.3 2.337 2.083 /mm.sup.1 9.869 3.804 F(000) 1096.882 1006.512 Crystal size/mm.sup.3 0.35 0.32 0.2 0.02 0.01 0.001 Radiation Cu K ( = 1.54184 ) Cu K ( = 1.54184 ) 2 range for data 3.2830 to 29.7570 2.69 to 24.75 collection Index ranges 19 h 17, 16 h 16, 17 k 18, 16 k 16, 12 l 12 13 l 12 Reflections 13268 5363 collected Independent 5197[R(int) = 0.0527] 754[R(int) = 0.0971] reflections Data/restraints/ 5197/1/218 754/6/42 parameters Goodness-of-fit 0.7291 1.0373 on F.sup.2 Final R indexes R.sub.1 = 0.0362, R.sub.1 = 0.0656, [ I >= 2 (I)] wR.sub.2 = 0.0949 wR.sub.2 = 0.1898 Final R indexes R.sub.1 = 0.0506, R.sub.1 = 0.1320, [all data] wR.sub.2 = 0.1056 wR.sub.2 = 0.2201 Largest diff. 1.5931/1.5709 1.3997/1.8505 peak/hole/e .sup.3

    [0241] The section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described in any way.

    [0242] It is appreciated that certain features of the disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination or as suitable in any other described embodiment of the disclosure. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.