INORGANIC SEMICONDUCTING COMPOUNDS

Abstract

Provided are compounds of the formula M.sup.A.sub.1-xM.sup.B.sub.xX.sup.A.sub.1-yX.sup.B.sub.yQ.sup.A.sub.1-zQ.sup.B.sub.z, wherein M.sup.A and M.sup.B are selected from Si, Ge, Sn, and Pb, X.sup.A and X.sup.B are selected from F, Cl, Br and I, Q.sup.A and Q.sup.B are selected from P, As, Sb and Bi, and x, y and z are 0 to 0.5, as well as doped variants thereof, useful as semiconducting materials. Due a double helix structure formed by the constituting atoms, the compounds are particularly suitable to provide nano-materials, in particular nanowires, for diverse applications.

Claims

1. A compound of formula (Ia):
M.sup.A.sub.1-xM.sup.B.sub.xX.sup.A.sub.1-yX.sup.B.sub.yQ.sup.A.sub.1-zQ.sup.B.sub.z(Ia), wherein: M.sup.A is an element selected from Si, Ge, Sn, and Pb, M.sup.B is an element selected from Si, Ge, Sn, and Pb and from combinations thereof such that M.sup.B is not the same as M.sup.A and does not contain M.sup.A, and x is 0 to 0.50; X.sup.A is an element selected from F, Cl, Br and I, X.sup.B is an element selected from F, Cl, Br and I and from combinations thereof such that X.sup.B is not the same as X.sup.A and does not contain X.sup.A, and y is 0 to 0.50; Q.sup.A is an element selected from P, As, Sb and Bi, Q.sup.B is an element selected from P, As, Sb and Bi and from combinations thereof such that Q.sup.B is not the same as Q.sup.A and does not contain Q.sup.A, z is 0 to 0.50; or a compound which is a doped variant of the compound of formula (Ia), and which further contains: an element M.sup.D, selected from Al, Ga, In and from combinations thereof, in a maximum amount of 10 mol % based on the total molar amount of M.sup.A and M.sup.B, which element M.sup.D may partially replace M.sup.A and/or M.sup.B in formula (Ia); and/or an element Q.sup.D, selected from S, Se, Te and from combinations thereof, in a maximum amount of 10 mol % based on the total molar amount of X.sup.A, X.sup.B, Q.sup.A and Q.sup.B, which element Q.sup.D may partially replace X.sup.A, X.sup.B, Q.sup.A and/or Q.sup.B in formula (Ia).

2. The compound in accordance with claim 1, which is a compound of formula (II):
(M.sup.A.sub.1-xM.sup.B.sub.x).sub.1-3mM.sup.D.sub.2mX.sup.A.sub.1-yX.sup.B.sub.y(Q.sup.A.sub.1-zQ.sup.B.sub.z).sub.1-2nQ.sup.D.sub.n(II), wherein M.sup.A, M.sup.B, X.sup.A, X.sup.B, Q.sup.A, Q.sup.B, x, y and z are defined as in claim 1, and wherein M.sup.D is an element selected from Al, Ga and In and from combinations thereof, Q.sup.D is an element selected from S, Se and Te and from combinations thereof, m is 0 to 0.03; and n is 0 to 0.10.

3. The compound in accordance with claim 2, which is a compound of formula (IIIa), (IIIb), (IIIc) or (IIId):
M.sup.A.sub.1-3mM.sup.D.sub.2mX.sup.A(Q.sup.A.sub.1-zQ.sup.B.sub.z).sub.1-2nQ.sup.D.sub.n(IIIa),
M.sup.A.sub.1-3mM.sup.D.sub.2mX.sup.A.sub.1-yX.sup.B.sub.yQ.sup.A.sub.1-2nQ.sup.D.sub.n(IIIb),
(M.sup.A.sub.1-xM.sup.B.sub.x).sub.1-3mM.sup.D.sub.2mX.sup.AQ.sup.A.sub.1-2nQ.sup.D.sub.n(IIIc),
M.sup.A.sub.1-3mM.sup.D.sub.2mX.sup.AQ.sup.A.sub.1-2nQ.sup.D.sub.n(IIId), wherein M.sup.A, M.sup.B, X.sup.A, X.sup.B, Q.sup.A, Q.sup.B, M.sup.D, x, y, z, m and n are defined as in claim 2.

4. The compound in accordance with claim 1, which is a compound of formula (IVa), (IVb), (IVc) or (IVd)
M.sup.AX.sup.AQ.sup.A.sub.1-zQ.sup.B.sub.z(IVa),
M.sup.AX.sup.A.sub.1-yX.sup.BQ.sup.A(IVb),
M.sup.A.sub.1-xM.sup.B.sub.xX.sup.AQ.sup.A(IVc),
M.sup.AX.sup.AQ.sup.A(IVd), wherein M.sup.A, M.sup.B, X.sup.A, Q.sup.A, x, y and z, are defined as in claim 1.

5. The compound of claim 2, wherein m is 0 to 0.01 and n is 0 to 0.01.

6. The compound of claim 1, wherein x is 0 to 0.15, y is 0 to 0.15 and z is 0 to 0.15.

7. The compound of claim 1, wherein M.sup.A is Sn.

8. The compound of claim 1, wherein X.sup.A is I.

9. The compound of claim 1, wherein Q.sup.A is P.

10. The compound in accordance with claim 1, which is selected from GeIP, GeBrP, GeClP, GeFP, GeIAs, GeBrAs, GeClAs, GeFAs, SnIP, SnBrP, SnClP, SnFP, SnIAs, SnBrAs, SnClAs, SnFAs, SnISb, SnBrSb, SnClSb, SnFSb, PbIP, PbBrP, PbClP, PbFP, PbIAs, PbBrAs, PbClAs, PbFAs, PbIBi, PbBrBi, PbClBi, and PbFBi.

11. The compound of claim 1, which is in the form of a nanowire.

12. A process for the production of the compound in accordance with claim 11, comprising the steps of: a) mixing starting materials selected from (i) elements contained in the compound, (ii) precursor compounds formed from elements contained in the compound, and (iii) combinations of (i) and (ii) in the desired stoichiometric amounts; b) reacting the starting materials under heat in an inert atmosphere; and c) exfoliating the obtained material to prepare the compound in the form of a nanowire.

13. A solar cell, a thermoelectric device or a sensor comprising the compound of claim 1.

14. An electrical, electronic, optical, or optoelectronic device comprising a compound of claim 1.

15. A method of photocatalysis, comprising reacting a reagent in the presence of a compound of claim 1 and light.

Description

EXAMPLES

[0159] Synthesis of SnIP:

[0160] Microcrystalline SnIP was prepared either by reaction of the elements in stoichiometric amounts or by the reaction of Sn, SnI.sub.4 and P in evacuated silica ampoule at 673 K. All glassware has been dried at 105? in an oven over night. Each ampoule was washed with acetone prior to the usage. The temperature program is as following: 0.8 K/min heating to 673 K, holding for 10 h and cooling with 5 K/h. Single crystals were prepared by heating Sn, SnI.sub.4 and red P (20 mg, 10 mg and 500 mg) up to 923 K (1.3 K/min) in an evacuated silica tube and holding for 5 h. The cooling was done stepwise first with 2 K/h to 773 K, after 15 h it was cooled down to room temperature with a cooling rate of 1.2 K/h. A SEM picture of the obtained microcrystals is shown in FIG. 2.

[0161] By exfoliation with common tape, nanosized crystals with a diameter smaller than 40 nm and an aspect ratio of >1000 (aspect ratio: quotient of length to diameter) were prepared. The tape method was applied previously for other 2D materials as graphene. Nano wires of even smaller diameters down to single strand wires were prepared by optimized exfoliation (with tape e.g. Lensguard 7568 by Nitto) or by dispersing in chloroform.

[0162] Chemical Analysis:

[0163] Elemental analysis shows Sn:P:I 40.0:11.26:44.2 wt.-%. The theoretical values are: 42.92:11.2:45.88. Energy dispersive X-ray spectroscopy (EDX) has been performed leading to a composition of SnIP of Sn 33(1): P 34(2): I 33(1) at.-%. Theoretical values: 33:33:33 at.-%.

[0164] Structure Determination:

[0165] The crystal structure of SnIP (see FIGS. 1a and 1b) has been determined from a single crystal by X-ray diffraction and has been substantiated by X-ray powder diffraction of a microcrystalline sample. Lattice parameters and selected crystallographic data are: The crystal structure of SnIP: Stoe IPDS II diffractometer, MoK.sub.? radiation, ?=0.71069 ?, T=293 K, crystal dimensions 0.01?0.01?0.2 mm.sup.3, monoclinic, space group P2/c (No. 13), lattice parameters a=7.934(2) ?, b=9.802(3) ?, c=18.439(9) ?, ?=110.06(5?), V=1347.0(9) ?.sup.3, Z=14. ? (calc.)=4.772 g cm.sup.?3, ? (MoK.sub.?)=14.81 mm.sup.?1, numerical absorption correction, crystal description using X reflections, full matrix least squares refinement on F.sup.2 using Jana2006 [Petricek, V., et al., Z. Kristallogr. 2014, 229, 345.], 6796 reflections, 3567 unique ones, ? max=29.13?, 98 parameters, R.sub.int 0.0859, R1 (1651Fo>3?(Fo))=0.0407, wR2=0.0840, GoF=1.02, residual electron density+1.88/?1.98 e ?.sup.3.

[0166] Bond distances within the helices of d(SnI)=3.060(2) to 3.288(3) ? for the tin-iodide helix and of d(PP)=2.170(4) to 2.211(5) ? for the phosphorus helix were determined. Each chiral single tube is either left or right handed and stacked in an hexagonal rod packed arrangement along the a axis. Tubes of a given chirality are arranged in rows, stacked along the b axis.

[0167] Electron localization function (ELF) analysis of SnIP showed the covalent character of the PP bonds and the strong polarization of the Sn lone pair towards the outer sphere of the tubes. A dative ionic interaction between the two helices can be assumed from the ELF between the Sn and P atoms. Two lone pairs of P are pointing towards the Sn positions creating bond lengths of d(SnP)=2.669(3) to 2.708(3) ?. This interaction is comparable to the H-bond system in Deoxyribose Nucleic Acid (DNA),

[0168] The purity was substantiated by comparing the single crystal structure data and the measured powder diffractogram (see FIG. 3).

[0169] Spectroscopic Characterization:

[0170] Solid State NMR spectroscopy, Mossbauer spectroscopy and magnetic measurements have been performed, substantiating the crystal structure and oxidation states of Sn in SnIP. It contains Sn.sup.2+, I.sup.? and P.sup.? (see FIGS. 4 to 7)

[0171] Exfoliation and dispersion of SnIP:

[0172] Double-helical tubes of SnIP are attracted to each other by van der Waals interactions and can therefore be exfoliated to provide nanotubes or bundles of nanotubes. SnIP was mechanically exfoliated to small bundles of nanotubes by the scotch tape approach. SnIP was fixed between two Nitto Lensguard 7568 tape foils, the two foils were pressed together and separated afterwards. This process was repeated up to the point when the demanded thickness of the bundles of nanotubes was reached. White light interferometry was used to determine the thickness or diameter of such mechanically exfoliated nanotubes.

[0173] Also SnIP nanotubes or bundles of nanotubes were separated via dispersion in organic solvents by the aid of an ultrasonic bath to accelerate the separation process. A summary is given in Table 1. SnIP is not soluble in water.

TABLE-US-00001 TABLE 1 Solubility of SnIP in different solvents. All solutions have been tested for the occurrence of iodide by silver nitrate (formation and crystallization of AgI). solubility (coloring Iodide of solution) present AgNO.sub.3/HNO.sub.3 Water ? ? Aceton + (yellow/brown) + + Acetonitril + (yellow) + + Isopropanol + (pale yellow) + + DMF + (pale yellow) + + DMSO ? (pale yellow) ? ? NMP + (grey, suspension) ? ? Toluol + (grey, some yellow) ? ? Ethanol + (yellow) + + Chloroform + (brown suspension) ? ? Dichloromethane + (brown suspension) ? ? + positive; ? negative

[0174] Bundles of nanotubes prepared by these methods are shown in FIGS. 8a to 8c, showing high resolution SEM pictures of exfoliated SnIP crystals. 8a: Mechanically (tape method) delaminated crystals of 30 nm diameter of SnIP. 8b: Chemically exfoliated SnIP crystal of the same size prepared on a copper grid. 8c: SnIP exfoliated and suspended in chloroform. Coils of SnIP nano tubes with diameters between 5 to 10 nm are provided after evaporation of the solvent.

[0175] Mechanical Properties of SnIP:

[0176] Crystals of SnIP show a very high mechanical flexibility and elasticity. Even large crystals of 1-2 mm length and a thickness of some ?m can be bent by 180?. Afterwards, the crystals rearrange without any visible deformation to their original position. This experiment has been performed using a conventional light microscope.

[0177] Electronic Properties

[0178] Quantum chemical calculations were performed in the framework of density functional theory (DFT) with LDA and PBE-GGA functionals. To confirm the results, full geometry optimizations were performed with two codes: the projector-augmented-wave (PAW) approach and the conjugant gradient algorithm as implemented in vasp (Kresse G., Furthm?ller J., Phys. Rev. B 1996, 54, 11169, Kresse G., Hafner J., J. Phys.: Condens. Matter 1994, 6 8245). Convergence is considered at differences in total energy less than 10.sup.?5 eV and maximum Hellmann-Feynmann forces of 10.sup.?4 eV/A. Additionally, the all-electron local orbital approach was applied with the Schlegel algorithm as implemented in the program CRYSTAL14 (Dovesi et al. CRYSTAL14 User's Manual. University of Torino: Torino, 2014. Dovesi, R. et al., Int. J. Quantum Chem., 2014, 114, 1287). Thereby, also the Grimme-d2 correction was used to account for dispersion (VdW) interactions.

[0179] For bulk-SnIP a band gap of 1.22 eV was observed while a single, non-coordinated SnIP nano tube is characterized by only a slightly larger band gap of 1.29 eV. Due to the determined values SnIP is exactly located in the band gap range of classical semiconductors like Si (ca. 1.1 eV) or GaAs (1.4 eV).

[0180] The direct band gap was determined by diffuse reflectance spectroscopy (see FIG. 15) to 1.86 eV and the indirect one to 1.80 eV.

[0181] SnIP shows a room temperature photoluminescence with an luminescence maximum at 1.86 eV in perfect accordance to the value determined from diffuse reflectance measurements (FIG. 16).

[0182] Quantum chemical DFT calculations with the HSE06 functional (J. P. Perdew, Y. Wang, Accurate and simple analytic representation of the electron-gas correlation energy. Phys. Rev. B. 45, 13244-13249 (1992), V. Krukau, 0. A. Vydrov, A. F. Izmaylov, G. E. Scuseria. Influence of the exchange screening parameter on the performance of screened hybrid functionals. J. Chem. Phys. 125, 224106 (2006)), a more suitable functional for the determination of the electronic structure (band structure), resulted in a direct band gap of 1.79 eV, in perfect accordance to the measured value.

[0183] Synthesis of GeIP and GelAs

[0184] Microcrystalline GeIP and GelAs were prepared by reactions of the elements in stoichiometric ratio in evacuated silica ampoules at 773 K. All glassware was dried at 105? in an oven over night. Each ampoule was washed with acetone prior to the usage. GeIP: Amounts are 146.2 mg Ge, 255.8 mg I.sub.2, and 62.4 mg P; GelAs: 130.9 mg Ge, 228.9 mg I.sub.2 and 135.2 mg As. The temperature program is as follows: in 10 h from room temperature to 773 K, holding the temperature for five days and finally cooling the samples to room temperature within 48 h. Microphotographs of the obtained needle shaped microcrystals are shown in FIG. 10 (GeIP) and 11 (GelAs).

[0185] Elemental Analysis

[0186] Energy dispersive X-ray spectroscopy (EDX) has been performed for GeIP leading to a composition of Ge 28(4): P 35(4): I 37(5) at.-%. Theoretical values: 33:33:33 at.-%.

[0187] Synthesis of PbIP and PbBrP

[0188] Microcrystalline PbIP and PbBrP were prepared by reactions of PbI.sub.2 or PbBr.sub.2 with red phosphorus and lead in stoichiometric ratio in evacuated silica ampoules, in the temperature interval of 643 to 693 K. All glassware has been dried at 105? in an oven over night. Each ampoule was washed with acetone prior to the usage. PbIP: Amounts are 40.0 mg P, 297.8 mg PbI.sub.2, and 133.7 mg Pb; PbBrP: 40.3 mg P, 236.4 mg PbBr.sub.2, and 133.6 mg Pb. The temperature program is as follows: in 8 h from room temperature to the target temperature, holding the temperature for 10 h and finally cooling the samples to room temperature within 75 h. Microphotographs of the obtained needle shaped microcrystals are shown in FIG. 12 (PbIP) and 13 (PbBrP).

[0189] Elemental Analysis

[0190] Energy dispersive X-ray spectroscopy (EDX) has been performed for PbIP and shows Pb 34(1): P 35(1):I 31(3) at.-%. Theoretical values: 33:33:33 at.-%.

[0191] Synthesis of Sn.sub.0.5Pb.sub.0.5/P

[0192] Microcrystalline Sn.sub.0.5Pb.sub.0.5IP were prepared by reactions of PbI.sub.2, Sn and red phosphorus in stoichiometric ratio in evacuated silica ampoules, in the temperature interval of 643 to 693 K. All glassware has been dried at 105? in an oven over night. Each ampoule was washed with acetone prior to the usage. 39.9 mg P, 76.9 mg Sn, 297.3 mg PbI.sub.2 were reacted to result in Sn.sub.05Pb.sub.05IP. The temperature program is as following in 10 h from room temperature to the target temperature, holding the temperature for 10 h and finally cooling the samples to room temperature within 75 h. Microphotographs of the obtained needle shaped microcrystals are shown in FIG. 14.

[0193] Calculated Isotypic Structures

[0194] The effects of substitution of the elements in isotypic compounds MXQ were estimated from DFT calculations. Assuming structures that are isotypic to experimentally found SnIP all structural parameters were relaxed. Predicted structures are summarized in Table 2. According to the results (1) the structure of SnIP is preserved for all substitutions, (2) the elements M and X have a systematic effect on lattice parameters a, b, c, and R, (3) the substitutions have a systematic effect on the electronic band gap. Conclusion (1) is underlined by the fact that the P substructure is maintained and all PP distances are found in the range between 2.17 and 2.20 ? upon substitution similar to SnIP (all further atomic distances are summarized in Table 3 according to the description of FIG. 9). Estimating Vegard's law for partial substitution Sn.sub.1-xM.sub.xI.sub.1-xX.sub.xP expected lattice parameters are obtained from SnIP by linear interpolation to the respective compound for full substitution MXP. (Hint on the applied method DFT-LDA slightly underestimates bond lengths and lattice parameters by 1-3%). From the lattice parameter effects (2) upon substitution we expect tunable mechanical properties. The same is predicted for electronic and optic properties from changes of the electronic band structure.

TABLE-US-00002 TABLE 2 Predicted lattice parameters from DFT calculations for completely substituted compounds MXQ for M = Pb, Sn, Ge, Si, X = F, Cl, Br, I, Q = P. An error of +/? 5% for each value must be taken into account. M X Q a/? b/? c/? ?/? V/?.sup.3 ?/gcm.sup.?3 ?Eg/eV Pb I P 8.11 9.63 18.82 109.73 1310.3 6.48 1.32 Sn I P 7.84 9.57 17.96 110.31 1257.8 5.11 1.22 Ge I P 7.50 9.26 17.30 110.31 1126.8 4.76 1.50 Si I P 7.26 9.19 17.30 110.36 1081.0 4.00 1.16 Pb Br P 8.17 8.97 17.08 112.22 1158.4 6.38 1.19 Sn Br P 7.92 8.83 17.15 112.60 1107.1 4.82 1.21 Ge Br P 7.54 8.63 16.49 112.55 991.0 4.30 1.65 Si Br P 7.26 8.53 16.59 113.48 942.4 3.43 1.35 Pb Cl P 8.29 8.51 16.58 114.77 1061.8 5.99 1.12 Sn Cl P 8.02 8.31 16.70 115.23 1006.2 4.28 1.15 Ge Cl P 7.62 8.13 15.97 113.95 904.1 3.58 1.51 Si Cl P 7.34 7.92 15.93 111.63 861.5 2.55 1.09 Pb F P 8.72 7.91 14.41 121.23 849.9 7.03 1.45 Sn F P 8.40 7.31 14.70 122.76 758.6 5.17 0.01 Ge F P 7.82 7.41 14.64 118.01 749.4 3.80 1.32 Si F P 7.61 7.25 14.57 118.63 705.7 2.57 0.25

TABLE-US-00003 TABLE 3 Predicted lattice parameters from DFT-LDA calculations for completely substituted compounds MXQ for M = Pb, Sn, Ge, Si, X = F, Cl, Br, I, Q = P. An error of +/? 5% for each value must be taken into account. distances helix Q [?] distances helix MX [?] Q3-Q3 Q2-Q3 Q1-Q2 Q4-Q1 X3-M2 M3-X3 M3-X2 M4-X2 M2-X1 M1-X1 M1-X4 PbIP 2.16 2.18 2.18 2.20 3.21 3.15 3.21 3.11 3.20 3.22 3.21 SnIP 2.20 2.19 2.20 2.21 3.29 3.06 3.21 3.06 3.12 3.18 3.17 GeIP 2.18 2.20 2.20 2.21 3.06 2.89 3.03 2.89 2.95 2.99 3.01 SiIP 2.19 2.21 2.21 2.21 3.07 2.78 3.00 2.82 2.82 2.97 2.91 PbBrP 2.16 2.17 2.18 2.19 3.09 2.98 3.03 2.96 3.01 3.04 3.03 SnBrP 2.17 2.18 2.19 2.19 2.98 2.88 2.97 2.89 2.93 2.94 2.98 GeBrP 2.18 2.18 2.19 2.19 2.92 2.69 2.89 2.73 2.74 2.85 2.82 SiBrP 2.20 2.20 2.20 2.20 3.18 2.49 2.94 2.65 2.47 3.04 2.61 PbClP 2.17 2.17 2.17 2.18 2.99 2.85 2.92 2.86 2.87 2.95 2.90 SnClP 2.17 2.17 2.18 2.18 2.88 2.75 2.85 2.79 2.79 2.83 2.86 GeClP 2.17 2.17 2.19 2.19 2.54 2.66 2.70 2.64 2.95 2.49 2.95 SiClP 2.16 2.18 2.20 2.21 2.27 2.75 2.44 2.58 3.35 2.24 3.03 PbFP 2.18 2.18 2.17 2.15 2.92 2.55 2.87 2.38 2.29 3.50 2.35 SnFP 2.19 2.18 2.17 2.16 2.51 2.49 2.90 2.39 2.15 3.24 2.39 GeFP 2.19 2.16 2.17 2.18 1.88 3.40 2.01 2.33 3.55 1.86 3.06 SiFP 2.18 2.17 2.18 2.18 1.67 3.47 1.82 2.28 3.62 1.66 3.23

DESCRIPTION OF FIGURES

[0195] FIG. 1 shows the crystal structure of SnIP with a view along the a axis (FIG. 1a) and b axis (FIG. 1b).

[0196] FIG. 2 shows an SEM picture of (bulk) SnIP.

[0197] FIG. 3 shows a comparison of a measured X-ray powder diffractogram of SnIP and a X-ray powder diffractogram calculated from single crystal structure data. Measurement was performed at room temperature.

[0198] FIG. 4 show the results of Raman spectroscopy of SnIP at room temperature.

[0199] FIG. 5 shows Mossbauer spectra of SnIP at 298 (top) and 77 K (bottom).

[0200] FIG. 6 shows the susceptibility of SnIP.

[0201] FIG. 7 shows the .sup.31P solid state NMR spectrum of SnIP.

[0202] FIG. 8 shows high resolution SEM pictures of exfoliated SnIP crystals. 8a: Mechanically (tape method) delaminated crystals of 30 nm diameter of SnIP. 8b: Chemically delaminated SnIP crystal of the same size prepared on a copper grid. 8c: TEM measurement of a SnIP nano tube with around 10 nm.

[0203] FIG. 9 shows the structure and bond lengths in MQX compounds, as predicted by DFT calculations for M=Pb, Sn, Ge, Si, X=F, Cl, Br, I, Q=P (see Table 2, Table 3, and Text).

[0204] FIG. 10 shows microphotographs of GeIP.

[0205] FIG. 11 shows microphotographs of GelAs.

[0206] FIG. 12 shows microphotographs of PbIP.

[0207] FIG. 13 shows microphotographs of PbBrP.

[0208] FIG. 14 shows microphotographs of Sn.sub.0.5Pb.sub.0.5IP

[0209] FIG. 15 shows the results from diffuse reflectance measurements of SnIP, drawn according the Kubelka-Munk theory. The direct band gap was calculated to 1.86 eV.

[0210] FIG. 16 shows the room temperature photoluminescence of SnIP with a luminescence maximum at 1.86 eV.