Abstract
A phosphor may have the empirical formula:
(AB).sub.1+x+2yAl.sub.11xy(AC).sub.xLi.sub.yO.sub.17:E, where 0<x+y<11; AC=Mg, Ca, Sr, Ba and/or Zn; AB=Na, K, Rb, and/or Cs; and E=Eu, Ce, Yb, and/or Mn. The phosphor may be used in conversion LED components.
Claims
1. A phosphor having the empirical formula (AB).sub.1+x+2yAl.sub.11xy(AC).sub.xLi.sub.yO.sub.17:E; wherein: 0<x+y<11; AC=Mg, Ca, Sr, Ba and/or Zn; AB=Na, K, Rb, and/or Cs; and E=Eu, Ce, Yb, and/or Mn.
2. A phosphor as claimed in claim 1, wherein x>0; and y>0.
3. A phosphor as claimed in claim 1, wherein 0<x+y<2.
4. A phosphor as claimed in claim 2, wherein the empirical formula is Na.sub.1+x+2yAl.sub.11xy(AC).sub.xLi.sub.yO.sub.17:E.
5. A phosphor as claimed in claim 2, wherein the empirical formula is Na.sub.1+x+2yAl.sub.11xy(Zn.sub.1zA.sub.z).sub.xLi.sub.yO.sub.17:E; wherein 0z<1; and wherein A=Mg, Ca, Sr, and/or Ba.
6. A phosphor as claimed in claim 2, wherein the empirical formula is Na.sub.1+x+2yAl.sub.11xyZn.sub.xLi.sub.yO.sub.17:E.
7. A phosphor as claimed in claim 2, wherein the empirical formula is Na.sub.1+x+2yAl.sub.11xy(Mg.sub.1zA.sub.z).sub.xLi.sub.yO.sub.17:E; wherein 0z<1; and wherein A=Zn, Ca, Sr, Ba, and combinations thereof.
8. A phosphor as claimed in claim 2, wherein the empirical formula is Na.sub.1+x+2yAl.sub.11xyMg.sub.xLi.sub.yO.sub.17:E.
9. A phosphor as claimed in claim 2, wherein the phosphor crystallizes in a trigonal crystal system.
10. A phosphor as claimed in claim 2, wherein the phosphor crystallizes in a R3 m 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.; C) calcining the blend at a temperature T1 ranging from 1200 to 1800 C. for an amount of time ranging from 6 hours to 15 hours.
12. A conversion LED component comprising: a primary radiation source that emits electromagnetic primary radiation in the operation of the conversion LED; and a conversion element comprising a phosphor as claimed in claim 1; wherein the conversion element is arranged in a beam path of the electromagnetic primary radiation and 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 is composed of 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
[0166] Further advantageous embodiments and developments are apparent from the working examples described hereinafter in conjunction with the figures.
[0167] FIGS. 1, 2, 13, 14 show characteristic properties of working examples of the phosphor,
[0168] FIGS. 3 and 15 show results of energy-dispersive x-ray analysis of working examples of the phosphor,
[0169] FIGS. 4 and 16 show sections of the crystal structure of the phosphor,
[0170] FIGS. 5 and 17 show Rietveld refinements of x-ray powder diffractograms of working examples of the phosphor,
[0171] FIGS. 6 and 18 show absorption and emission spectra of working examples of the phosphor,
[0172] FIG. 7 shows the quantum efficiency as a function of the excitation wavelength of a working example of the phosphor,
[0173] FIG. 19 shows emission spectra of working examples of the phosphor,
[0174] FIGS. 8, 10, 20 show a comparison of emission spectra,
[0175] FIG. 9 shows the Kubelka-Munk functions for a working example of the phosphor and comparative examples,
[0176] FIGS. 11 and 21 show comparisons of optical properties of working examples of phosphor with comparative examples,
[0177] FIG. 12 shows the thermal quenching characteristics of a working example of the phosphor,
[0178] FIGS. 22 and 23 show schematic side views of conversion LEDs.
[0179] 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
[0180] FIG. 1 shows crystallographic data of Na.sub.1+x+2yAl.sub.11xyZn.sub.xLi.sub.yO.sub.17:Eu with x=0.7 and y=0.3 (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, Li, Al and O. It was assumed that Li, Al and Zn occupy the same crystallographic position, and so refinement was possible with inclusion of Li 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 Zn 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 zinc-containing reactants, especially ZnO. 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.1+x+2yAl.sub.11xy(AC).sub.xLi.sub.yO.sub.17:Eu, especially Na.sub.1+x+2yAl.sub.11xyZn.sub.xLi.sub.yO.sub.17:Eu, the presence of Li and AC, especially of Li and Zn, has thus been found to be essential.
[0181] FIG. 2 shows atom positions in the structure of Na.sub.2.3Al.sub.10Zn.sub.0.7Li.sub.0.3O.sub.17:Eu.sup.2+ (WE1). Within the structure, Li, Al and Zn occupied the crystallographic position A14/Li4.
[0182] FIGS. 3 and 16 show the trigonal crystal structure of the phosphors Na.sub.2.3Al.sub.10Zn.sub.0.7Li.sub.0.3O.sub.17:Eu.sup.2+ and Na.sub.2.1Al.sub.10.2Mg.sub.0.5Li.sub.0.3O.sub.17:Eu.sup.2+ in a schematic diagram from somewhat different viewing directions, but both roughly about [001]. The crystal structure is composed of spinel-type blocks in which Al, Li and Zn or Al, Li and Mg occupy the centers (not shown) of edge- and vertex-linked octahedra ((Al,Li,Zn)O.sub.6 octahedron or (Al,Li,Mg)O.sub.6 octahedron) and the centers of vertex-linked tetrahedra ((Al,Li,Zn)O.sub.4 tetrahedron or (Al,Li,Mg)O.sub.4 tetrahedron). The spineltype 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 Zn, and Al, Li and Mg, respectively occupy the same position within the crystal structure as Al within the crystal structure of sodium -aluminate.
[0183] 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.1+x+2yAl.sub.11xyZn.sub.xLi.sub.yO.sub.17:Eu with x=0.7 and y=0.3. For the Rietveld refinement, the atom parameters for sodium -aluminate were used in order to show that the crystal structure of Na.sub.1+x+2yAl.sub.11xyZn.sub.xLi.sub.yO.sub.17:Eu with x=0.7 and y=0.3 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+x+2yAl.sub.11yZn.sub.xLi.sub.yO.sub.17:Eu with x=0.7 and y=0.3. The lower diagram shows the differences of the measured and calculated reflections. No secondary phases, especially no secondary phases containing Na, Zn, 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.
[0184] 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.2.3Al.sub.10Zn.sub.0.7Li.sub.0.3O.sub.17:Eu.sup.2+. The excitation spectrum was recorded at 535 nm. In the case excitation of the phosphor with primary radiation of 460 nm, the phosphor shows a peak wavelength of about 535 nm with a half-height width of about 65 nm. The quantum efficiency is more than 90%. The color locus in the CIE color space is at the coordinates CIE-x:0.323 and CIE-y:0.633.
[0185] FIG. 7 shows the absolute quantum efficiency (QE.sub.a) of the first working example WE1 of the inventive phosphor having the empirical formula Na.sub.2.3Al.sub.10Zn.sub.0.7Li.sub.0.3O.sub.17:Eu.sup.2+ as a function of the excitation wavelength and hence the wavelength of the primary radiation. It is apparent that the phosphor can be efficiently excited up to at least a wavelength of the primary radiation of 480 nm. Variation of the concentration of Eu and optimization of the synthesis of the phosphor can lead to a further improvement in the optical properties of the phosphor.
[0186] FIG. 8 shows a comparison of emission spectra. The emission spectra of the first working example Na.sub.2.3Al.sub.10Zn.sub.0.7Li.sub.0.3O.sub.17:Eu.sup.2+ (excitation with primary radiation of 460 nm) and two further working examples Na.sub.1.72Li.sub.0.3Al.sub.10.66O.sub.17:Eu.sup.2+ and Na.sub.1.57Zn.sub.0.57Al.sub.10.43O.sub.17:Eu.sup.2+ (excitation with primary radiation of 400 nm) are shown. The undoped compounds Na.sub.1.72Li.sub.0.3Al.sub.10.66O.sub.17 and Na.sub.1.57Zn.sub.0.57Al.sub.10.43O.sub.17 are known from the literature and, just like the phosphors, crystallize in a crystal structure isotypic with sodium -aluminate. A comparison of the phosphors Na.sub.2.3Al.sub.10Zn.sub.0.7Li.sub.0.3O.sub.17:Eu.sup.2+ with Na.sub.1.72Li.sub.0.3Al.sub.10.66O.sub.17:Eu.sup.2+ and Na.sub.1.57Zn.sub.0.57Al.sub.10.43O.sub.17:Eu.sup.2+ shows that the phosphor containing both Li and Zn has a peak length closer to 555 nm and a smaller half-height width. This is shown by the comparison of the emission spectra. Na.sub.1.72Li.sub.0.3Al.sub.10.66O.sub.17:Eu.sup.2+ and Na.sub.1.57Zn.sub.0.57Al.sub.10.43O.sub.17:Eu.sup.2+ show a peak wavelength in the blue to blue/green region (peak=490 nm for Na.sub.1.57Zn.sub.0.57Al.sub.10.43O.sub.17:Eu.sup.2+ and (peak=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 (peak=535 nm) with a half-height width of about 65 nm. By contrast with Na.sub.2.3Al.sub.10Zn.sub.0.7Li.sub.0.3O.sub.17:Eu.sup.2+, Na.sub.1.72Li.sub.0.3Al.sub.10.66O.sub.17:Eu.sup.2+ and Na.sub.1.57Zn.sub.0.57Al.sub.10.43O.sub.17:Eu.sup.2+ are colorless solids.
[0187] 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 and the two further working examples Na.sub.1.72Li.sub.0.3Al.sub.10.66O.sub.17:Eu.sup.2+ and Na.sub.1.57Zn.sub.0.57Al.sub.10.43O.sub.17:Eu.sup.2+.
[0188] 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.
[0189] It is apparent from FIG. 9 that K/S for the working examples Na.sub.1.72Li.sub.0.3Al.sub.10.66O.sub.17:Eu.sup.2+ and Na.sub.1.57Zn.sub.0.57Al.sub.10.43O.sub.17:Eu.sup.2+ drops more steeply toward longer wavelengths than for the first working example of the phosphor and no longer shows any absorption from about 425 nm, whereas the first working example has significant absorption up to 500 nm.
[0190] FIG. 10 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+ and (Sr,Ba).sub.2SiO.sub.4:Eu.sup.2+. 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.2.3Al.sub.10Zn.sub.0.7Li.sub.0.3O.sub.17:Eu.sup.2+ 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.
[0191] The dominant wavelength is a means of describing non-spectral (polychromatic) light mixtures in terms of spectral (monochromatic) light that produces a similar perceived shade. In the CIE color space, the line that connects a point for a particular color and the point CIE-x=0.333, CIE-y=0.333 can be extrapolated such that it meets the outline of the space at two points. The point of intersection closer to said color represents the dominant wavelength of the color as the wavelength of the pure spectral color at this point of intersection. The dominant wavelength is thus the wavelength that is perceived by the human eye.
[0192] FIG. 11 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+ and (Sr,Ba).sub.2SiO.sub.4:Eu.sup.2+. 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.
[0193] In FIG. 12, relative brightness in % is plotted against temperature in C. It is a comparison of the thermal quenching characteristics of the inventive phosphor WE1 by comparison with the two comparative examples Lu.sub.3(Al,Ga).sub.5O.sub.12:Ce.sup.3+ and (Sr,Ba).sub.2SiO.sub.4:Eu.sup.2+. It is apparent that the first working example Na.sub.2.3Al.sub.10Zn.sub.0.7Li.sub.0.3O.sub.17:Eu.sup.2+ of the phosphor has higher thermal stability than (Sr,Ba).sub.2SiO.sub.4 and comparable thermal stability to Lu.sub.3(Al,Ga).sub.5O.sub.12:Ce.sup.3+. The phosphors have been excited with blue primary radiation having a wavelength of 460 nm at different temperatures of 25 to 225 C. and their relative brightness has been recorded. The inventive phosphor WE1 is suitable for use thereof in conversion LEDs in which the phosphor may typically be subjected to higher temperatures, for example up to 140 C.
[0194] Advantageously, the phosphor may thus also be used at higher operating temperatures in conversion LEDs.
[0195] FIG. 13 shows crystallographic data of Na.sub.1+x+2yAl.sub.11yMg.sub.xLi.sub.yO.sub.17:Eu with x=0.5 and y=0.3 (WE2). The crystal structure was determined and refined using x-ray diffraction data of a single crystal of the phosphor. The structure refinement included Na, Mg, Al and O. It was assumed that Li, Al and Mg occupy the same crystallographic position, and so refinement was possible including Mg and Al only, especially since refinement of three atoms that share a crystallographic position is not possible in a viable manner. Energy-dispersive x-ray spectroscopy detected the presence of Mg in the phosphor. The results are shown in FIG. 15. Energy-dispersive x-ray spectroscopy serves for qualitative or semiquantitative detection of elements; conclusions as to the exact quantity of the elements cannot be made therefrom. The particular values should thus not be regarded as percentages with respect to the exact quantity of the elements. Owing to its low molecular mass, Li cannot be detected by means of energy-dispersive x-ray spectroscopy. Moreover, comparative experiments show that the phosphor does not form without the addition of lithium-containing reactants, especially Li.sub.2CO.sub.3. The use of a lithium-containing reactant, especially Li.sub.2CO.sub.3, is thus found to be essential for the formation of the phosphor WE2. Synthesis without Li.sub.2CO.sub.3 led to a colorless product that emits secondary radiation in the blue region of the electromagnetic spectrum on excitation with UV radiation. In order to achieve emission in the green spectral region and a small half-height width of (AB).sub.1+x+2yAl.sub.11xy(AC).sub.xLi.sub.yO.sub.17:Eu, especially Na.sub.1+x+2yAl.sub.11yMg.sub.xLi.sub.yO.sub.17:Eu, the presence of Li and AC, especially of Li and Mg, has thus been found to be essential.
[0196] FIG. 14 shows atom positions in the structure of Na.sub.2.1Al.sub.10.2Mg.sub.0.5Li.sub.0.3O.sub.17:Eu.sup.2+ (WE2). Within the structure, Li, Al and Mg occupied the crystallographic position Al3/Mg3.
[0197] In FIG. 17 there is a crystallographic evaluation. FIG. 17 shows a Rietveld refinement of the x-ray powder diffractogram of the second working example WE2, i.e. for Na.sub.2.1Al.sub.10.2Mg.sub.0.5Li.sub.0.3O.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.2.1Al.sub.10.2Mg.sub.0.5Li.sub.0.3O.sub.17:Eu.sup.2+ is isotypic with that of sodium -aluminate. The upper diagram shows the superposition of the reflections measured with the reflections calculated for Na.sub.2.1Al.sub.10.2Mg.sub.0.5Li.sub.0.3O.sub.17:Eu.sup.2+. The lower diagram shows the differences of the reflections measured and calculated. No secondary phases are observed; more particularly, no secondary phases containing Na, Mg, Li and O are formed, 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.
[0198] FIG. 18 shows the emission spectrum (ES) and the excitation spectrum (AS) of a powder sample of the second working example WE2 of the phosphor having the empirical formula Na.sub.2.1Al.sub.10.2Mg.sub.0.5Li.sub.0.3O.sub.17:Eu.sup.2+. The excitation spectrum was recorded at 535 nm. On excitation of the phosphor with primary radiation at 460 nm, the phosphor shows a peak wavelength of about 543 nm with a half-height width of about 70 nm. The quantum efficiency is more than 89%. The color locus in the CIE color space is at the coordinates CIE-x:0.374 and CIE-y:0.599.
[0199] FIG. 19 shows a comparison of emission spectra of the first and second working examples. The phosphors were excited with primary radiation of wavelength 460 nm. The substitution of Zn for Mg results in a shift in the peak wavelength toward longer wavelengths.
[0200] FIG. 20 shows the emission spectra of the second working example (WE2) of the phosphor and two comparative examples Lu.sub.3(Al,Ga).sub.5O.sub.12:Ce.sup.3+ and Sr.sub.2Si.sub.2O.sub.2N.sub.2:Eu.sup.2+. All three phosphors show a similar dominant wavelength in the region of 561 nm. It is apparent that the phosphor 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 Na.sub.2.1Al.sub.10.2Mg.sub.0.5Li.sub.0.3O.sub.17:Eu.sup.2+ 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.
[0201] FIG. 21 shows a comparison of the optical data of the second working example (WE2) of the phosphor and two comparative examples Lu.sub.3(Al,Ga).sub.5O.sub.12:Ce.sup.3+ and Sr.sub.2Si.sub.2O.sub.2N.sub.2:Eu.sup.2+. It is apparent that WE2 shows a higher relative quantum efficiency than Sr.sub.2Si.sub.2O.sub.2N.sub.2:Eu.sup.2+. This is significant in particular in that the phosphor has not been optimized with regard to the synthesis, and so, after an optimized synthesis, the quantum efficiency could be higher than for Lu.sub.3(Al,Ga).sub.5O.sub.12:Ce.sup.3+.
[0202] The conversion LED according to FIG. 22 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 and 500 nm inclusive. The conversion element 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.2.1Al.sub.10.2Mg.sub.0.5Li.sub.0.3O.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.
[0203] 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.
[0204] The conversion LED 1 according to FIG. 23 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.2.3Al.sub.10Zn.sub.0.7Li.sub.0.3O.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.
[0205] 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
[0206] ppm parts per million
[0207] dom dominant wavelength
[0208] peak peak wavelength
[0209] wavelength
[0210] FWHM half-height width
[0211] LER light yield
[0212] QE.sub.a absolute quantum efficiency
[0213] QE.sub.r relative quantum efficiency
[0214] AS excitation spectrum
[0215] ES emission spectrum
[0216] K/S Kubelka-Munk function
[0217] t time
[0218] T temperature
[0219] I intensity
[0220] C. degrees Celsius
[0221] E emission
[0222] En energy
[0223] LED light-emitting diode
[0224] nm nanometer
[0225] lm lumen
[0226] W watt
[0227] 2 degrees 2 theta
[0228] 1 conversion LED
[0229] 2 layer sequence/semiconductor chip
[0230] 2a radiation exit surface
[0231] 3 conversion element
[0232] 10 substrate
[0233] 11 housing
[0234] S beam path of primary radiation
