LED PHOSPHOR COMPRISING BOW-TIE SHAPED A2N6 BUILDING BLOCKS

Abstract

The invention provides, amongst others for application in a lighting unit, a phosphor selected from the class of

M.sub.2D.sub.2C.sub.2-2bB.sub.bA.sub.2N.sub.6:Ln   (I)

with M=selected from the group consisting of divalent Ca, Sr, and Ba; D=selected from the group consisting of monovalent Li, divalent Mg, Mn, Zn, Cd, and trivalent Al and Ga; C=selected from the group consisting of monovalent Li and Cu; B=selected from the group consisting of divalent Mg, Zn, Mn and Cd; A=selected from the group consisting of tetravalent Si, Ge, Ti, and Hf; Ln=selected from the group consisting of ES and RE; ES=selected from the group consisting of divalent Eu, Sm and Yb; RE=selected from the group consisting of trivalent Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Tm; and 0≦b≦1.

Claims

1. A lighting unit comprising a light source, configured to generate light source light and a luminescent material configured to convert at least part of the light source light into luminescent material light, wherein the light source comprises a light emitting diode (LED), and wherein the luminescent material comprises a phosphor selected from the class of
M.sub.2D.sub.2C.sub.2-2bB.sub.bA.sub.2N.sub.6:Ln   (I) wherein M=one or more selected from the group consisting of divalent Ca, Sr, and Ba; D=one or more selected from the group consisting of monovalent Li, divalent Mg, Mn, Zn, Cd, and trivalent Al and Ga; C=one or more selected from the group consisting of monovalent Li and Cu; B=one or more selected from the group consisting of divalent Mg, Zn, Mn and Cd; A=one or more selected from the group consisting of tetravalent Si, Ge, Ti, and Hf; Ln=one or more selected from the group consisting of ES and RE; ES=one or more selected from the group consisting of divalent Eu, Sm and Yb; RE=one or more selected from the group consisting of trivalent Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Tm; and wherein 0≦b ≦1.

2. The lighting unit of claim 1, wherein M comprises one or more of Ca and Sr, wherein D comprises Mg, wherein C comprises Li and b=0, wherein A comprises Si, and wherein Ln comprises one or more of divalent Eu and trivalent Ce.

3. The lighting unit of claim 1, wherein the phosphor comprises (M.sub.1-x).sub.2D.sub.2C.sub.2-2bB.sub.bA.sub.2N.sub.6:Eu.sub.x, wherein 0<x≦0.2.

4. The lighting unit of claim 1, wherein the phosphor comprises (M.sub.1-y).sub.2D.sub.2C.sub.2−2bB.sub.bA.sub.2N.sub.6:Ce.sub.y, wherein 0<y≦0.2.

5. The lighting unit of claim 1, wherein the phosphor comprises M.sub.2Mg.sub.2Li.sub.2Si.sub.2N.sub.6:Ln, wherein M comprises one or more of Ca and Sr.

6. The lighting unit of claim 1, wherein the luminescent material further comprises one or more other phosphors selected from the group consisting of a divalent europium containing nitride luminescent material, a divalent europium containing oxonitride luminescent material, a trivalent cerium containing garnet and a trivalent cerium containing oxonitride, and wherein the light source is configured to generate blue light.

7. A phosphor selected from the class of
M.sub.2D.sub.2C.sub.2-2bB.sub.bA.sub.2N.sub.6:Ln   (I) with M=one or more selected from the group consisting of divalent Ca, Sr, and Ba D=one or more selected from the group consisting of monovalent Li, divalent Mg, Mn, Zn, Cd, and trivalent Al and Ga; C=one or more selected from the group consisting of monovalent Li and Cu; B=one or more selected from the group consisting of divalent Mg, Zn, Mn and Cd; A=one or more selected from the group consisting of tetravalent Si, Ge, Ti, and Hf; Ln=one or more selected from the group consisting of ES and RE; ES=one or more selected from the group consisting of divalent Eu, Sm and Yb; RE=one or more selected from the group consisting of trivalent Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Tm; and wherein 0≦b ≦1.

8. The phosphor of claim 7, wherein the phosphor comprises M.sub.2D.sub.2C.sub.2-2bB.sub.bA.sub.2N.sub.6:Ln (I), wherein M comprises one or more of Ca and Sr, wherein D comprises Mg, wherein C comprises Li and b=0, wherein A comprises Si, and wherein Ln comprises one or more of divalent Eu and trivalent Ce.

9. The phosphor of claim 7, wherein the phosphor comprises (M.sub.1-x).sub.2D.sub.2C.sub.2-2bB.sub.bA.sub.2N.sub.6:Eux, wherein 0<x≦0.2.

10. The phosphor of claim 7, wherein the phosphor comprises (M.sub.1-y).sub.2D.sub.2C.sub.2-2bB.sub.bA.sub.2N.sub.6:Ce.sub.y, wherein 0<y≦0.2.

11. The phosphor of claim 7, wherein the phosphor comprises M.sub.2Mg.sub.2Li.sub.2Si.sub.2N.sub.6:Ln, wherein M comprises one or more of Ca and Sr.

12. The phosphor of claim 7, wherein the phosphor comprises phosphor particles having a coating, wherein the coating comprises one or more coating selected from the group consisting of an AlPO4 coating, an Al.sub.2O.sub.3 coating and a SiO.sub.2 coating.

13. A method for making a phosphor, the method comprising steps of: combining a selection of starting materials to form the phosphor in the class of,
M.sub.2D.sub.2C.sub.2-2bB.sub.bA.sub.2N.sub.6:Ln (I) wherein M=one or more selected from the group consisting of divalent Ca, Sr, and Ba D=one or more selected from the group consisting of monovalent Li, divalent Mg, Mn, Zn, Cd, and trivalent Al and Ga; C=one or more selected from the group consisting of monovalent Li and Cu; B=one or more selected from the group consisting of divalent Mg, Zn, Mn and Cd; A=one or more selected from the group consisting of tetravalent Si, Ge, Ti, and Hf; Ln=one or more selected from the group consisting of ES and RE; ES=one or more selected from the group consisting of divalent Eu, Sm and Yb; RE=one or more selected from the group consisting of trivalent Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Tm; and wherein 0<b <1; and heating the starting materials at a temperature in a range of about 800° C. to about 1300° C.

14. The method of claim 13, wherein Ln comprises one or more of Eu and Ce, and wherein the heating is performed in a reducing atmosphere.

15. The lighting unit of claim 1, further comprising a backlighting unit of an LCD display device.

16. The lighting unit of claim 1, further comprising at least a portion of a projection system.

17. The lighting unit of claim 1, further comprising at least a portion of a self-lit display system.

18. The lighting unit of claim 1, further comprising at least a portion of a pixelated display system.

19. The lighting unit of claim 1, further comprising at least a portion of a segmented display system.

20. The lighting unit of claim 1, further comprising at least a portion medical lighting system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0104] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

[0105] FIGS. 1a-1d schematically depict some embodiments of the lighting unit; the drawings are not necessarily on scale;

[0106] FIG. 2:(a) view along the a-axis and [0107] (b) along c-axis of M.sub.2-xD.sub.2C.sub.2A.sub.2N.sub.6. 1: M atoms, 3: C atoms, 2: A.sub.2N.sub.6 bow tie units, nitrogen atoms: 5. 4: Edge connected tetrahedra chains DN.sub.4/2 running along a;

[0108] FIG. 3: view along a of M.sub.2-2xD.sub.2BA.sub.2N.sub.6. Monovalent C atoms are fully replaced by divalent B atoms 6;

[0109] FIG. 4: Threefold coordination of C atoms and octahedral coordination of two C atoms (a), Fourfold coordination of B atoms in M.sub.2-2xD.sub.2C.sub.2-2bB.sub.bA.sub.2N.sub.6:Ln (b);

[0110] FIG. 5: XRD diffraction pattern of Ca.sub.2Mg.sub.2Li.sub.2Si.sub.2N.sub.6:Eu. CaO secondary phase reflections are marked with stars;

[0111] FIG. 6: Excitation (monitored at 635 nm) and emission (440 nm excitation) specra of example 1;

[0112] FIG. 7: Excitation (monitored at 635 nm) and emission (440 nm excitation) specra of example 2;

[0113] FIG. 8: Excitation (monitored at 634 nm) and emission (460 nm excitation) specra of example 3; and

[0114] FIG. 9: Emission spectrum of the LED of example 10.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0115] FIG. 1a schematically depicts an embodiment of the lighting unit, indicated with reference 100, of the invention. The lighting unit comprises a light source 10, which is in this schematic drawing a LED (light emitting diode). In this embodiment, on top of the light source 10, here on the (light exit) surface 15, thus downstream of the light source 10, a luminescent material 20 is provided. This luminescent material 20 comprises phosphor as described herein, indicated with reference 40. By way of example, the lighting unit 100 further comprises, for instance for light extraction properties, a (transmissive) dome 61. This is an embodiment of a transmissive optical element 60, which is in this embodiment arranged downstream of the light source 10 and also downstream of the light conversion layer 20. The light source 10 provides light source light 11 (not indicated in the drawing), which is at least partly converted by the light conversion layer 20, at least by phosphor 40, into luminescent material light 51. The light emanating from the lighting unit is indicated with reference 101, and contains at least this luminescent material light 51, but optionally, dependent upon the absorption of luminescent material 50 also light source light 11.

[0116] FIG. 1b schematically depicts another embodiment, without dome, but with an optional coating 62. This coating 62 is a further example of a transmissive optical element 60. Note that the coating 62 may in an embodiment be one or more of a polymeric layer, a silicone layer, or an epoxy layer. Alternatively or additionally a coating of silicon dioxide and/or silicon nitride may be applied.

[0117] In both schematically depicted embodiment of FIGS. 1a-1b, the luminescent material 20 is in physical contact with the light source 10, or at least its light exit surface (i.e. surface 15), such as the die of a LED. In FIG. 1c, however, the luminescent material 20 is arranged remote from the light source 10. In this embodiment, the luminescent material 20 is configured upstream of a transmissive (i.e. light transmissive) support 30, such as an exit window. The surface of the support 30, to which the light conversion layer 20 is applied, is indicated with reference 65. Note that the luminescent material 20 may also be arranged downstream of the support 30, or at both sides of the support luminescent material 20 may be applied. The distance between the luminescent material 20 and the light source (especially its light exit surface 15) is indicated with reference dl, and may be in the range of 0.1 mm-10 cm. Note that in the configuration of FIG. 1c, in principle also more than one light source 10 may be applied.

[0118] FIG. 1 d is schematically the same as FIG. 1c, but now with a plurality of light sources 10.

[0119] Optionally, the luminescent material is shaped into a self-supporting layer, such as a ceramic material. In such instance, the transmissive optical element 60 may not be necessary, but may nevertheless be present.

EXPERIMENTAL

[0120] As indicated above, synthesis of the claimed materials can be carried out by a variety of processing methods. It has been found by the inventors that keeping firing temperatures in the range of 800-1300° C. improves phase purity and luminescence properties of the claimed phases. It turned out that reactive precursors like intermetallic phases obtained by melting of the constituent M, D, C, B, A and rare earth/lanthanide metals, alkaline earth amides, or silicon diimide are especially suitable. The addition of flux materials like fluorides or chlorides is also improving phase formation. Suitable synthesis methods comprise high pressure nitridation, processing in alkaline metal melts, ammonothermal synthesis and standard mix and fire approaches.

Example 1

Ca.SUB.1.99.Mg.SUB.2.Li.SUB.2.Si.SUB.2.N.SUB.6.:Eu.SUB.0.01 .(i.e. (Ca.SUB.0.995.Eu.SUB.0.005.).SUB.2.Mg.SUB.2.Li.SUB.2.Si.SUB.2.N.SUB.6.; i.e. x=0.005)

[0121] 5.531 g (131.4 mmole) CaH.sub.2, 5.611 g (40 mmole) Si.sub.3N.sub.4, 1.393 g (40 mmole) Li.sub.3N, 2.917 g (120 mmole) Mg, and 0.125 g (0.6 mmole) EuF3 are mixed and sintered under forming gas (5% H.sub.2) at 1100° C. for 2 h.

[0122] The powder phosphor was analyzed by means of powder XRD with silicon as internal standard. The phosphor crystallizes in the monoclinic Ca.sub.2Mg.sub.2Li.sub.2Si.sub.2N.sub.6 structure with lattice constants a=5.5579 Å, b=9.8285 Å, c=6.0050 Å and β=97.25°. FIG. 5 shows the powder XRD pattern of the raw phosphor powder. CaO secondary phase is removed by washing with ammonia solution. Excitation at 440 nm leads to emission in the red spectral range with a peak emission at 639 nm, and a spectral width FWHM=1550 cm.sup.−1 (CIE color coordinates x,y=0.687, 0.313, lumen equivalent LE=129.4 1m/W). The spectra are depicted in FIG. 6. The inventors believe that the three excitation maxima located at ˜410, 460 and 550 nm are due to the reduced symmetry of the octahedral EuN.sub.6 coordination that removes the energetic degeneracy of the three 5d t.sub.2g states in an ideal octahedral coordination.

Example 2

(Ca.SUB.0.8.Sr.SUB.0.2.).SUB.1.99.Mg.SUB.2.Li.SUB.2.Si.SUB.2.N.SUB.6.:Eu.SUB.0.01 .(i.e. (Ca.SUB.0.796.Sr.SUB.0.199.Eu.SUB.0.005.).SUB.2.Mg.SUB.2.Li.SUB.2.Si.SUB.2.N.SUB.6.; i.e. x=0.005)

[0123] 4.021 g (95.52 mmole) CaH.sub.2, 2.141 g SrH.sub.2 (23.88 mmole), 5.611 g (40 mmole) Si.sub.3N.sub.4, 1.393 g (40 mmole) Li.sub.3N, 2.917 g (120 mmole) Mg, and 0.125 g (0.6 mmole) EuF3 are mixed and sintered in forming gas (5% H.sub.2) at 1100° C. for 2 h.

[0124] The powder phosphor was analyzed by means of powder XRD with silicon as internal standard. The phosphor crystallizes in the monoclinic Ca.sub.2Mg.sub.2Li.sub.2Si.sub.2N.sub.6 structure with lattice constants a=5.5636 Å, b=9.8376 Å, c=6.0126 Å and β=97.26°. (Ca,Sr)O secondary phase is removed by washing with ammonia solution. Excitation at 440 nm leads to emission in the red spectral range with a peak emission at 635 nm, and a spectral width FWHM=1510 cm.sup.−1 (CIE color coordinates x,y=0.680, 0.320, lumen equivalent LE=154.1 lm/W). The spectral blue shift of emission compared to example 1) is due to expansion of the host lattice by incorporation of the larger Sr atoms. Excitation and emission are shown in FIG. 7.

Example 3

Ca.SUB.1.84.Sr.SUB.0.14.Mg.SUB.2.Li.SUB.2.Si.SUB.2.N.SUB.6.:Eu.SUB.0.02 .(i.e. (Ca.SUB.0.92.Sr.SUB.0.07.Eu.SUB.0.01.)2Mg.SUB.2.Li.SUB.2.Si.SUB.2.N.SUB.6.; i.e. x=0.01)

[0125] 5 g (0.05 mole) Mg.sub.3N.sub.2, 18.8 g (0.15 mole) SrF.sub.2, 33.5 g (0.1 mole) Mg.sub.3Ca.sub.3N.sub.2F.sub.6 prepared by mixing Mg.sub.3N.sub.2 and CaF.sub.2 and firing the mixture under nitrogen at 950° C., 11.6 g (0.2 mole) Si(NH).sub.2, 9.8 g Li.sub.3N (0.2 mole), 13.9 g (2 mole) Li and 0.2 g (0.001 mole) EuF.sub.3 are mixed and fired for 24 hrs in a sealed tantalum reaction container at 950° C. Orange microcrystals of Ca.sub.1.84Sr0.14Mg.sub.2Li.sub.2Si.sub.2N.sub.6:Eu.sub.0.02 are separated from the raw product powder by screening. Analysis of the material with EDX shows a composition that corresponds with that analyzed by means of X ray powder diffraction and Rietvelt refinement. Table 5 lists the EDX analysis results in weight %.

TABLE-US-00005 TABLE 5 EDX analysis results for Ca.sub.1.84Sr.sub.0.14Mg.sub.2Li.sub.2Si.sub.2N.sub.6:Eu.sub.0.02 in weight %. Li cannot be detected with EDX. Ca Sr Mg Si N Eu 13.38 0.87 13.61 13.55 58.00 0.09

[0126] Excitation and emission are shown in FIG. 8.

[0127] Below, some alternative preparation methods for Ca.sub.1.99Mg.sub.2Li.sub.2Si.sub.2N.sub.6:Eu.sub.0.01 (see also example 1) are described.

Example 4

[0128] 4.188 g (99.5 mmole) CaH.sub.2, 1.161 g (33.3 mmole) Li.sub.3N, 8.041 g (100.0 mmole) MgSiN.sub.2, and 0.088 g (0.25 mmole) Eu.sub.2O.sub.3 are mixed and subsequently sintered under nitrogen gas at 1100° C. for 5 h. The precursor MgSiN.sub.2 was synthesized by mixing 3.364 g (33.3 mmole) Mg.sub.3N.sub.2 and 4.676 g (33.3 mmole) Si.sub.3N.sub.4 and sintering under forming gas (5% H.sub.2) at 1250° C. for 3 h. Excitation at 444 nm leads to an emission in the red spectral range with a peak emission at 638 nm, and a spectral width FWHM=1451 cm.sup.−1.

Example 5

[0129] 4.188 g (99.5 mmole) CaH.sub.2, 1.161 g (33.3 mmole) Li.sub.3N, 3.836 g (50.0 mmole) Mg.sub.2Si, 1.404 g (50.0 mmole) Si, and 0.088 g (0.25 mmole) Eu.sub.2O.sub.3 are mixed and subsequently sintered under nitrogen gas at 1000° C. for 5 h. Excitation at 444 nm leads to an emission in the red spectral range with a peak emission at 637 nm, and a spectral width FWHM=1480 cm.sup.−1.

Example 6

[0130] 4.917 g (33.1 mmole) Ca.sub.3N.sub.2, 1.161 g (33.3 mmole) Li.sub.3N, 3.364 g (33.3 mmole) Mg.sub.3N.sub.2 (or 2.431 g (100.0 mmole) Mg), and 0.104 g (0.5 mmole) EuF.sub.3 are mixed and subsequently sintered under nitrogen gas at 1100° C. for 5 h. Excitation at 444 nm leads to an emission in the red spectral range with a peak emission at 639 nm, and a spectral width FWHM=1549 cm.sup.−1.

Example 7

[0131] 6.782 g (99.5 mmole) CaSi, 1.161 g (33.3 mmole) Li.sub.3N, 3.364 g (33.3 mmole) Mg.sub.3N.sub.2 (or 2.431 g (100.0 mmole) Mg), and 0.104 g (0.5 mmole) EuF.sub.3 are mixed and subsequently sintered under nitrogen gas at 1000° C. for 5 h. The precursor CaSi was synthesized by mixing 4.209 g (100.0 mmole) CaH.sub.2 and 2.809 g (100.0 mole) Si and sintering under nitrogen at 975° C. for 3 h.

Example 8

[0132] 5.182 g (50.0 mmole) CaSi.sub.2:Eu, 2.094 g (49.75 mmole) CaH.sub.2, 1.161 g (33.3 mmole) Li.sub.3N, 2.431 g (100.0 mmole) Mg, and 0.052 g (0.25 mmole) EuF.sub.3 are mixed and sintered in forming gas (5% H.sub.2) at 1100° C. for 2 h. The precursor CaSi.sub.2:Eu was obtained by mixing 4.188 g (99.5 mmole) CaH.sub.2, 5.617 g (200.0 mmole) Si, and 0.088 g (0.25 mmole) Eu.sub.2O.sub.3, followed by sintering in argon atmosphere at 975° C. for 3 h. Excitation at 444 nm leads to emission in the red spectral range with a peak emission at 639 nm, and a spectral width FWHM=1421cm.sup.−1.

Example 9

[0133] 9.303 g (100.0 mmole) CaMgSi:Eu, and 1.161 g (33.3 mmole) Li.sub.3N are mixed and sintered in forming gas (5% H.sub.2) at 1100° C. for 2 h. The precursor CaMgSi:Eu was received by mixing 4.188 g (99.5 mmole) CaH.sub.2, 2.431 g (100.0 mmole) Mg, 2.809 g (100.0 mmole) Si, and 0.088 g (0.25 mmole) Eu.sub.2O.sub.3, and sintering in argon atmosphere at 975° C. for 1.5 h. Excitation at 444 nm leads to an emission in the red spectral range with a peak emission at 638 nm, and a spectral width FWHM=1413 cm.sup.−1.

[0134] A summary of some date of the Examples is given in Table 6.

TABLE-US-00006 TABLE 6 summary of some optical data of the samples made in the Examples 1-9 LE Peak FWHM Rel PL Example x y [lm/W] [nm] [cm.sup.−1] Intensity 1 0.685 0.315 139 638 1420 1.00 2 0.672 0.328 155 635 1499 0.14 4 0.686 0.314 144 638 1451 0.38 5 0.683 0.317 146 637 1480 0.06 6 0.684 0.316 131 639 1549 0.18 8 0.686 0.314 135 639 1421 0.98 9 0.685 0.314 138 638 1413 0.88

Example 10

[0135] A mixture of the phosphor powder of example 1 and a commercially available green phosphor β-SiAlON:Eu in a heat curable silicone resin are dispensed in a LED package comprising a 441 nm emitting LED die in such a way that a CIE color point x,y=0.265, 0.2354 is realized (FIG. 9). Integration of the manufactured LEDs in an LCD backlighting unit results in a front of screen correlated color temperature of 8677K for the balanced white point (front of screen CIE color coordinate x,y=0.287,0.304). A color gamut performance of 94% (133%) NTSC (sRGB) is being reached. The emission spectrum of the LED of this example is shown in FIG. 9, with on the x-axis the wavelength (nm) and on the y-axis relative intensity (I) in arbitrary units.