Abstract
A phosphor may have the empirical formula: (AB).sub.1+x+2yAl.sub.11-x-y(AC).sub.xLi.sub.yO.sub.17:E, where 0<x+y<11; x>0; AC=B, Ga, In, or combinations thereof; AB=Na, K, Rb, Cs, or combinations thereof; and E=Eu, Ce, Yb, Mn, or combinations thereof. The phosphor may be used in conversion LED components.
Claims
1. A phosphor having the empirical formula (AB).sub.1+2yAl.sub.11-x-y(AC).sub.xLi.sub.yO.sub.17:E; wherein: 0<x+y<11; x>0; AC=B, Ga, In, or combinations thereof; AB=Na, K, Rb, Cs, or combinations thereof; and E=Eu, Ce, Yb, Mn, or combinations thereof.
2. A phosphor as claimed in claim 1, wherein 0<x+y<5; and y>0.
3. A phosphor as claimed in claim 1, wherein 0<x+y<5; 0<x3; and 0<y2.
4. A phosphor as claimed in claim 1, having the empirical formula Na.sub.1+2yAl.sub.1-x-y(AC).sub.xLi.sub.yO.sub.17:E where 0<x+y<5; 0<x3; and 0<y2.
5. A phosphor as claimed in claim 4, wherein 0x+y3; 0<x2; and 0<y1.
6. A phosphor as claimed in claim 1, wherein the empirical formula is Na.sub.1+2yAl.sub.11-x-y(Ga.sub.1-zA.sub.z).sub.xLi.sub.yO.sub.17:E; wherein: 0z<1; 0<x+y<5; 0<x3; 0<y2; A=B and/or In; and E=Eu, Ce, Yb, and/or Mn.
7. A phosphor as claimed in claim 1, wherein the empirical formula is Na.sub.1+2yAl.sub.11-x-yGa.sub.xLi.sub.yO.sub.17:E; wherein: 0<x+y<5; 0<x3; 0<y2; and E=Eu, Ce, Yb, Mn, or combinations thereof.
8. A phosphor as claimed in claim 7, wherein: 0x+y3; 0<x2; and 0<y1.
9. A phosphor as claimed in claim 1, which wherein the phosphor crystallizes in a trigonal crystal system.
10. A phosphor as claimed in claim 1, which wherein the phosphor crystallizes in a R3m space group.
11. A process for preparing a phosphor as claimed in claim 1, wherein the process comprises: blending reactants of the phosphor to form a blend; heating the blend to a temperature T1 ranging from 1200 to 1800 C.; calcining the blend at a temperature T1 ranging from 1200 to 1800 C. for an amount of time ranging from 5 hours to 10 hours.
12. A conversion LED component comprising: a primary radiation source that emits electromagnetic primary radiation in the operation of the conversion LED component; and a conversion element comprising a phosphor as claimed in claim 1; wherein the conversion element is arranged in the beam path of the electromagnetic primary radiation; and wherein the phosphor is configured to convert the electromagnetic primary radiation at least partly to the electromagnetic secondary radiation in the blue to green region of the electromagnetic spectrum.
13. The conversion LED component as claimed in claim 12, wherein the conversion LED component emits white total radiation in operation; and wherein the conversion element comprises a white phosphor configured to convert the electromagnetic primary radiation and/or the electromagnetic secondary radiation in the blue to green region at least partly to electromagnetic secondary radiation in the red region of the electromagnetic spectrum, and wherein the white total radiation comprises the primary and secondary radiations.
14. The conversion LED component as claimed in claim 12, wherein the conversion LED component in operation emits blue to green total radiation, wherein the blue to green total radiation corresponds to the secondary radiation.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0137] Further advantageous embodiments and developments are apparent from the working examples described hereinafter in conjunction with the figures.
[0138] FIGS. 1, 2 show characteristic properties of working examples of the phosphor,
[0139] FIG. 3 shows results of an energy-dispersive x-ray analysis of a working example of the phosphor,
[0140] FIG. 4 shows a section of the crystal structure of the phosphor,
[0141] FIG. 5 shows a Rietveld refinement of an x-ray powder diffractogram of a working example of the phosphor,
[0142] FIG. 6 shows an absorption and emission spectrum of a working example of the phosphor,
[0143] FIGS. 7, 9, 12 show a comparison of emission spectra of various phosphors,
[0144] FIGS. 8 and 10 show a comparison of Kubelka-Munk functions for various phosphors,
[0145] FIGS. 11 and 13 show comparisons of optical properties of various phosphors,
[0146] FIGS. 14 and 15 show schematic side views of conversion LEDs.
[0147] Elements that are identical, of identical type or act identically are provided with the same reference signs in the figures. The figures and the size relationships of the elements illustrated in the figures among one another should not be regarded as to scale. Rather, individual elements may be illustrated with an exaggerated size in order to enable better illustration and/or to afford a better understanding.
DETAILED DESCRIPTION
[0148] FIG. 1 shows crystallographic data of Na.sub.1.7Al.sub.10.25Ga.sub.0.35Li.sub.0.5O.sub.17:Eu.sup.2+ (WE1). The crystal structure was determined and refined using x-ray diffraction data of a single crystal of the phosphor. The structure refinement included Na, Ga, Al and O. It was assumed that Li, Al and Ga occupy the same crystallographic position, and so refinement was possible with inclusion of Ga and Al only, especially since free refinement of three atoms that share a crystallographic position is not possible in a viable manner. However, energy-dispersive x-ray spectroscopy detected the presence of Ga in the phosphor. The results are shown in FIG. 3. Energy-dispersive x-ray spectroscopy serves for qualitative or semiquantitative detection of elements and not for quantitative detection, which explains the different values from the measurements conducted. Owing to its low molecular mass, Li cannot be detected by means of energy-dispersive x-ray spectroscopy. Moreover, experiments show that the phosphor WE1 does not form without the addition of lithium-containing reactants, especially Li.sub.2CO.sub.3, or gallium-containing reactants, especially Ga.sub.2O.sub.3. Instead, these syntheses led to colorless products which, on excitation with UV radiation, emit secondary radiation in the blue region of the electromagnetic spectrum. In order to achieve emission in the green spectral region and a small half-height width of the inventive phosphor (AB).sub.2+2yAl.sub.11-x-y(AC).sub.xLi.sub.yO.sub.17:Eu, especially Na.sub.1+2yAl.sub.11-x-yGa.sub.xLi.sub.yO.sub.17:Eu, the presence of Li and AC, especially of Li and Ga, has thus been found to be essential.
[0149] FIG. 2 shows atom positions in the structure of Na.sub.1.7Al.sub.10.25Ga.sub.0.35Li.sub.0.5O.sub.17:Eu.sup.2+ (WE1). Within the structure, Li, Al and Ga occupied the crystallographic position Al3/Ga3.
[0150] FIG. 3 shows the trigonal crystal structure of the phosphor Na.sub.2.7Al.sub.10.25Ga.sub.0.3.5Li.sub.0.5O.sub.17:Eu.sup.2+ of a schematic diagram along [001]. The crystal structure is composed of spinel-type blocks in which Al, Li and Ga occupy the centers (not shown) of edge- and vertex-linked octahedra ((Al,Li,Ga)O.sub.6 octahedron and the centers of vertex-linked tetrahedra ((Al,Li,Ga)O.sub.4 tetrahedron. The spinel type blocks are separated by planes having freely mobile Na ions. The crystal structure is isotypic to the crystal structure of sodium -aluminate. Al, Li and Ga occupy the same position within the crystal structure as Al within the crystal structure of sodium -aluminate.
[0151] In FIG. 5 is a crystallographic evaluation. FIG. 5 shows a Rietveld refinement of an x-ray powder diffractogram of the first working example WE1, i.e. for Na.sub.2.7Al.sub.10.20Ga.sub.0.35Li.sub.0.5O.sub.17:Eu.sup.2+. For the Rietveld refinement, the atom parameters for sodium -aluminate were used in order to show that the crystal structure of Na.sub.1.7Al.sub.10.25Ga.sub.0.35Li.sub.0.5O.sub.17:Eu.sup.2+ is isotypic to that of sodium -aluminate. The above diagram shows the superposition of the reflections measured with the calculated reflections for Na.sub.1.7Al.sub.10.25Ga.sub.0.35Li.sub.0.5O.sub.17:Eu.sup.2+. The lower diagram shows the differences of the measured and calculated reflections. No secondary phases, especially no secondary phases containing Na, Ga, Li and O, are observed, and so it can be confirmed from the x-ray powder diffractogram that the phosphor contains all the reactants used. The differences in the intensity of the reflections are attributable to an as yet incomplete structure elucidation.
[0152] FIG. 6 shows the emission spectrum (ES) and the excitation spectrum (AS) of a powder sample of the first working example WE1 of the inventive phosphor having the empirical formula Na.sub.1.7Al.sub.10.25Ga.sub.0.35Li.sub.0.5O.sub.17:Eu.sup.2+. The excitation spectrum was recorded at 530 nm. In the case excitation of the phosphor with primary radiation of 460 nm, the phosphor shows a peak wavelength of about 530 nm with a half-height width of about 66 nm. The quantum efficiency is more than 90%. The color locus in the CIE color space is at the coordinates CIE-x:0.308 and CIE-y:0.628.
[0153] FIG. 7 shows a comparison of emission spectra. The emission spectra of the first working example Na.sub.1.7Al.sub.10.25Ga.sub.0.35Li.sub.0.5O.sub.17:Eu.sup.2+ (excitation with primary radiation of 460 nm), a fifth working example WE5 of the formula NaAl.sub.10.5Ga.sub.0.5O.sub.17:Eu.sup.2+ (2 mol %) (excitation with primary radiation of 400 nm) and a comparative example C1 of the formula Na.sub.1.72Al.sub.10.66Li.sub.0.3O.sub.17:Eu.sup.2+ (2 mol %) (excitation with primary radiation of 400 nm) are shown. WE1, WE5 and C1 crystallize in a crystal structure isotypic of sodium -aluminate. A comparison of the phosphor Na.sub.1.7Al.sub.10.25Ga.sub.0.35Li.sub.0.5O.sub.17:Eu.sup.2+ with NaAl.sub.10.5Ga.sub.0.5O.sub.17:Eu.sup.2+ and Na.sub.1.72Al.sub.10.66Li.sub.0.3O.sub.17:Eu.sup.2+ shows that the phosphor containing both Li and Ga has a peak wavelength closer to 555 nm and a smaller half-height width. This is shown by the comparison of the emission spectra. NaAl.sub.10.5Ga.sub.0.5O.sub.17:Eu.sup.2+ and Na.sub.1.72Al.sub.10.66Li.sub.0.3O.sub.17:Eu.sup.2+ show a peak wavelength in the blue to blue-green region (max=490 nm for NaAl.sub.10.5Ga.sub.0.5O.sub.17:Eu.sup.2+ and max=520 nm for Na.sub.1.72Li.sub.0.3Al.sub.10.66O.sub.17:Eu.sup.2+) with a half-height width exceeding 100 nm, whereas the first working example surprisingly shows radiation with a peak wavelength in the green region (max=530 nm) with a half-height width of about 66 nm. By contrast with Na.sub.1.7Al.sub.10.25Ga.sub.0.35Li.sub.0.5O.sub.17:Eu.sup.2+, Na.sub.1.72Li.sub.0.3Al.sub.10.66O.sub.17:Eu.sup.2+ and NaAl.sub.10.5Ga.sub.0.5O.sub.17:Eu.sup.2+ are colorless solids.
[0154] FIG. 9 shows a comparison of the normalized Kubelka-Munk function (K/S), plotted against wavelength in nm, for the first working example (WE1) of the phosphor, the fifth working example NaAl.sub.10.5Ga.sub.0.5O.sub.17:Eu.sup.2+ (WE5) and the comparative example Na.sub.1.72Li.sub.0.3Al.sub.10.66O.sub.17:Eu.sup.2+ (C1).
[0155] K/S was calculated here as follows:
K/S=(1R.sub.inf).sup.2/2R.sub.inf where R.sub.inf corresponds to the diffuse reflection (reflectance) of the phosphors. High K/S values mean high absorption in this region.
[0156] It is apparent from FIG. 8 that K/S for the first working example WE1 drops less steeply toward longer wavelengths than for WE5 and C1, which no longer show any absorption from about 425 nm, whereas the first working example (WE1) has significant absorption up to 500 nm. The fifth working example can be excited in the near UV region.
[0157] FIG. 9 shows the emission spectra of the working examples Na.sub.1.7Al.sub.10.25Ga.sub.0.35Li.sub.0.5O.sub.17:Eu.sup.2+ (WE1), Na.sub.1.8Al.sub.9.6GaLi.sub.0.4O.sub.17:Eu.sup.2+ (WF2), Na.sub.2Al.sub.9.5GaLi.sub.0.5O.sub.17:Eu.sup.2+ (WE3) and Na.sub.2Al.sub.8.5Ga.sub.2Li.sub.0.5O.sub.17:Eu.sup.2+ (WE4) of the phosphor. All phosphors are excited with primary radiation of 460 nm. Surprisingly, the emission band or peak wavelength can be shifted by varying the lithium and/or gallium content. More particularly, the peak wavelength and hence also the dominant wavelength is shifted into the long-wave spectral region with rising lithium and/or gallium content and hence with greater y and/or x values within the empirical formula Na.sub.0+2yAl.sub.11-x-yGa.sub.xLi.sub.yO.sub.17:Eu. The optical data are summarized in FIG. 10. As is apparent, even within the working examples described, the peak wavelength (max) can be shifted in a region of 14 nm and the dominant wavelength in a region of 23. A higher gallium and/or lithium content than in the working examples described leads to peak wavelengths shifted further into the long-wave region. The possibility of adjusting or matching the emission of the phosphor means that the phosphor is of interest for many applications.
[0158] FIG. 11 shows a comparison of normalized Kubelka-Munk functions (K/S) for working examples WE1, WE2, WE3 and WE4. As is apparent, the absorption capacity in the blue region of the electromagnetic spectrum rises with increasing lithium and/or gallium content.
[0159] FIG. 12 shows the emission spectra of powder samples of the first working example (WE1) of the phosphor and two comparative examples Lu.sub.3(Al,Ga).sub.5O.sub.12:Ce.sup.3+ (LuAGaG) and (Sr,Ba).sub.2Si.sub.2O.sub.2N.sub.2:Eu.sup.2+ ((Sr,Ba)SiON). All phosphors were excited with primary radiation of 460 nm. All three phosphors show a similar dominant wavelength in the region of 555 nm. It is apparent that the inventive phosphor Na.sub.1+2yAl.sub.11-x-yGa.sub.xLi.sub.yO.sub.17:Eu has a smaller half-height width than the comparative examples. The smaller half-height width leads to an increase in overlap with the eye sensitivity curve. Thus, the inventive phosphor has a luminescence efficiency or light yield which is very high, and higher compared to the comparative examples. The smaller half-height width additionally leads to a more saturated color of the secondary radiation, which is reflected in a higher color purity.
[0160] FIG. 13 shows a comparison of the optical data of the first working example (WE1) of the phosphor and the two comparative examples Lu.sub.3 (Al,Ga).sub.5O.sub.12:Ce.sup.3+ (LuAGaG) and (Sr,Ba).sub.2Si.sub.2O.sub.2N.sub.2:Eu.sup.2+ ((Sr,Ba)SiON). It is apparent that WE1 shows a relative quantum efficiency above 100% and hence is much higher than that of the comparative examples. This is also significant in particular in that the phosphor has not been optimized with regard to the synthesis.
[0161] The conversion LED according to FIG. 14 has a layer sequence 2 disposed on a substrate 10. The substrate 10 may, for example, be reflective. Above the layer sequence 2 is disposed a conversion element 3 in the form of a layer. The layer sequence 2 has an active layer (not shown) which, in operation of the conversion LED, emits a primary radiation having a wavelength of 420 nm to 500 nm inclusive. The conversion element 3 is disposed in the beam path of the primary radiation S. The conversion element 3 includes a matrix material, for example a silicone, and particles of the phosphor Na.sub.1.7Al.sub.10.25Ga.sub.0.35Li.sub.0.5O.sub.17:Eu.sup.2+ having an average grain size of 10 m, which converts the primary radiation in operation of the conversion LED at least partly to a secondary radiation in the green region of the electromagnetic spectrum. In the conversion element 3, the phosphor is distributed homogeneously within the scope of manufacturing tolerance in the matrix material. The conversion element 3 has been applied over the full area of the radiation exit surface 2a of the layer sequence 2 and over the lateral faces of the layer sequence 2, and is in direct mechanical contact with the radiation exit surface 2a of the layer sequence 2 and the lateral faces of the layer sequence 2. The primary radiation can also exit via the lateral faces of the layer sequence 2.
[0162] The conversion element 3 may be applied, for example, by injection molding or compression-injection molding, or by spray-coating methods. In addition, the conversion LED has electrical contacts (not shown), the formation and arrangement of which is known to the person skilled in the art.
[0163] The conversion LED 1 according to FIG. 15 has a housing 11 with a recess. Disposed in the recess is a layer sequence 2 having an active layer (not shown) which, in operation of the conversion LED, emits primary radiation having a wavelength of 420 to 500 nm. The conversion element 3 takes the form of an encapsulation of the layer sequence 2 in the recess and includes a matrix material, for example a silicone, and a phosphor, for example Na.sub.1.8Al.sub.9.6GaLi.sub.0.4O.sub.17:Eu.sup.2+, which converts the primary radiation in operation of the conversion LED 1 at least partly to secondary radiation in the green region of the electromagnetic spectrum. It is also possible that the phosphor in the conversion element 3 is spatially concentrated above the radiation exit surface 2a. This can be achieved, for example, by sedimentation.
[0164] The invention is not limited to the working examples by the description with reference thereto. Instead, the invention includes every new feature and every combination of features, which especially includes any combination of features in the claims, even if this feature or this combination itself is not specified explicitly in the claims or working examples.
LIST OF REFERENCE NUMERALS
[0165] ppm parts per million [0166] dom dominant wavelength [0167] max peak wavelength [0168] wavelength [0169] FWHM half-height width [0170] LER light yield [0171] QE.sub.r relative quantum efficiency [0172] AS excitation spectrum [0173] ES emission spectrum [0174] K/S Kubelka-Munk function [0175] t time [0176] I intensity [0177] E emission [0178] LED light-emitting diode [0179] nm nanometer [0180] lm lumen [0181] W watt [0182] 2 degrees 2 theta [0183] 1 conversion LED [0184] 2 layer sequence/semiconductor chip [0185] 2a radiation exit surface [0186] 3 conversion element [0187] 10 substrate [0188] 11 housing [0189] S beam path of primary radiation
