White emitting light source and luminescent material

Abstract

The invention relates to a white emitting light source with an improved luminescent material of the formula (AEN2/3)*b(MN)*c(SiN4/3)*d1CeO3/2*d2EuO*xSiO2*yAlO3/2 wherein AE is an alkaline earth metal chosen of the group of Ca, Mg, Sr and Ba or mixtures thereof and M is a trivalent element chosen of the group of Al, B, Ga, Sc with d1>10*d2. In combination with a UV to blue light generating device this material leads to an improved light quality and stability, especially an improved temperature stability for a wide range of applications.

Claims

1. A luminescent material comprising: (AEN.sub.2/3)*b(MN)*c(SiN.sub.4/3)*d.sub.1CeO.sub.3/2*d.sub.2EuO*xSiO.sub.2*yAlO.sub.3/2 wherein AE is an alkaline earth metal chosen from a group consisting of Ca, Mg, Sr and Ba or mixtures thereof and M is a trivalent element chosen from a group consisting of Al, B, Ga, Sc or mixtures thereof, wherein
0.952*(a+d.sub.1+d.sub.2)/(b+c+x+y)1.2
a+d.sub.1+d.sub.2c+x,
(b+y):(c+x)1,
(b+y)1+10*d.sub.1,
b5*y,
c10*x,
0.0001d.sub.10.2 and d.sub.110*d.sub.2; wherein the surface roughness of at least one surface of the luminescent material, measured as the geometric mean of the difference between highest and deepest surface features is 0.001 m and 1 m.

2. The luminescent material of claim 1 wherein the luminescent material is a ceramic.

3. The luminescent material of claim 1 wherein the luminescent material is 95% (AEN.sub.2/3)*b(MN)*c(SiN.sub.4/3)*d.sub.1CeO.sub.3/2*d.sub.2EuO*xSiO.sub.2*yAlO.sub.3/2.

4. The luminescent material of claim 1 further comprising at least one flux.

5. The luminescent material of claim 4 wherein the at least one flux comprises an alkaline material.

6. The luminescent material of claim 4 wherein the at least one flux comprises one of a metal oxide and a fluoride.

7. The luminescent material of claim 4 wherein the at least one flux comprises one of SiON, SiAlON, and SiO.sub.2.

8. The luminescent material of claim 1 wherein (b+y):(c+x) is 1.01 and 1.20.

9. The luminescent material of claim 1 wherein (b+y) is 1+10*d.sub.1.

10. The luminescent material of claim 1 wherein b5*y and c10*x.

11. A device comprising: a blue LED; and a ceramic plate attached to the blue LED, the ceramic plate comprising a luminescent material, the luminescent material comprising (AEN.sub.2/3)*b(MN)*c(SiN.sub.4/3)*d.sub.1CeO.sub.3/2*d.sub.2EuO*xSiO.sub.2*yAlO.sub.3/2 wherein AE is an alkaline earth metal chosen from a group consisting of Ca, Mg, Sr and Ba or mixtures thereof and M is a trivalent element chosen from a group consisting of Al, B, Ga, Sc or mixtures thereof, wherein
0.92*(a+d.sub.1+d.sub.2)/(b+c+x+y)1.2
a+d.sub.1+d.sub.2c+x,
(b+y):(c+x)1,
(b+y)1+10*d.sub.1,
b5*y,
c10*x,
0.0001d.sub.10.2 and d.sub.110*d.sub.2 wherein the light output of the device has a uv0.025, 72Ra89 and 273LE337.

12. The device of claim 11 wherein the n-GaN layer is optically coupled to the ceramic plate by a transparent glue.

13. The device of claim 12 wherein the transparent glue is silicone.

14. The device of claim 12 wherein the transparent glue has an index of 1.5.

15. The device of claim 11 wherein a surface of the blue LED facing the ceramic plate is roughened.

16. The device of claim 15 wherein the ceramic plate forms a rigid mechanical protection for the blue LED.

17. The device of claim 15 wherein the surface roughness of at least one surface of the ceramic plate, measured as the geometric mean of the difference between highest and deepest surface features is 0.001 m and 1 m.

18. The device of claim 11 wherein a full width half maximum of an emission spectrum of the luminescent material is 120 nm.

19. The device of claim 11 wherein the emission spectrum of the luminescent material comprises: an emission maximum in a wavelength range between 500 and 600 nm having a full width half maximum of 80 nm; and an emission maximum in a wavelength range between 600 and 650 nm having a full width half maximum of 30 and 140 nm.

20. The device of claim 11 wherein combined light comprising light emitted by the blue LED and light emitted by the luminescent material has a correlated color temperature between 3000 and 4000 K.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Additional details, features, characteristics and advantages of the object of the invention are disclosed in the subclaims, the figures and the following description of the respective figures and examples, whichin an exemplary fashionshow several embodiments and examples of a luminescent material for use in an illumination system according to the invention as well as several embodiments and examples of an illumination system according to the invention.

(2) FIG. 1 shows two emission spectra of two illumination system according to the present invention with LEDs emitting at different blue wavelengths combined with the luminescent material according to Example I of the present invention.

(3) FIG. 2 shows CIE 1976 color coordinates of the two illumination systems of FIG. 1 with different thickness plates of the luminescent ceramics.

(4) FIG. 3 shows a zoom of FIG. 2 in the white region

(5) FIG. 4 shows several emission spectra of further illumination systems according to the present invention employing different thickness plates of the luminescent ceramics according to Example I of the present invention

(6) FIG. 5 shows further several emission spectra of further illuminations systems according to the present invention employing different thickness plates of the luminescent ceramics according to Example I of the present invention

(7) FIG. 6 shows a diagram of the x-y-color point coordinates against the temperature of a luminescent material according to Example I of the present invention.

(8) FIG. 7 shows a schematic diagram of illumination systems.

DETAILED DESCRIPTION OF EMBODIMENTS

(9) The invention will be further understood by the following Example I whichin a merely illustrative fashionshows several materials of the present invention.

Example I

(10) Example I refers to
1.080(CaN.sub.2/3)*1.006(AlN)*0.963(SiN.sub.4/3)*0.0198CeO.sub.3/2*0.0002EuO*0.018SiO.sub.2*0.014AlO.sub.3/2
which was prepared in the following fashion:

(11) All actions were carried out in dry inert gas atmosphere. 53.37 g Ca.sub.3N.sub.2 (2N), 41.02 g AlN (3N), 0.78 g Al.sub.2O.sub.3, 45.30 g Si.sub.3N.sub.4, 1.09 g SiO.sub.2, 3.41 g CeO.sub.2 (4N) and 0.035 g Eu.sub.2O.sub.3 (4N) were intimately mixed by ball milling and the mixture was subsequently fired in forming gas atmosphere (N.sub.2:H.sub.2 95:5 v/v) at 1500 C. maximum temperature. The obtained powder cake was again milled, granulated and pressed into pellets by uniaxial pressing and subsequent cold isostatic pressing until a green density of >50% was reached. The pellets were sintered at 1650 C. in forming gas atmosphere, optionally this is followed by a hot isostatic pressing step at 1 kbar N.sub.2 to improve the density.

(12) FIG. 7 shows a blue LED 1 and a blue LED 2 (=illuminations systems). Each of n-GaN layers 111A, 111B of LEDs 1, 2 are optically coupled by transparent glue 112A, 112B with a refractive index of 1.5 (silicone) to the luminescent ceramic plates 113A, 113B, which form the outer surfaces 121A, 121B of the illumination, systems 1, 2. Besides the optical functionality of the ceramic plates 113A, 113B they also form a rigid mechanical protection for the underlying roughened surfaces 120A, 120B of n-GaN layers 111A, 111B of the LEDs.

(13) FIG. 1 shows a white LED emission spectra with a luminescent ceramic plate made out of the material according to example I with 150 m thickness on blue LED 1 with a dominant emission wavelength of 450 nm and blue LED 2 with a dominant emission wavelength of 464 nm. As described above the 1 mm.sup.2 thin-film flip-chip InGaNGaN LEDs 1, 2 are optically coupled by a transparent glue 112A, 112B with a refractive index of 1.5 (silicone) to the luminescent ceramic plates 113A, 113B, which forms the outer surfaces 121A, 121B of the illumination systems. Besides the optical functionality of the ceramic plates 113A, 113B they also form a rigid mechanical protection for the underlying roughened surfaces 120A, 120B of n-GaN layers 111A, 111B of the LEDs.

(14) It can be seen that the material according to Example I has a broad band in the wavelength range of 500-700 nm leading to a warm-white emission spectrum of the illumination systems with a correlated color temperature (CCT) between 3000 and 4000 K.

(15) FIG. 2 shows the color points of the LEDs with luminescent ceramic plate (=illumination systems) of FIG. 1 together with the color points of the blue LEDs used in a CIE 1976 diagram.

(16) FIG. 3 shows a zoomed view on the white region of FIG. 2. In this view the specific property of the luminescent material is visible to counteract a variation of the blue LED emission. This property is very beneficial for white LEDs in general illumination applications to realize a stable white emission color (stable CCT), even if the LED emission spectrum undergoes changes due to variations in drive current and junction temperature.

(17) FIGS. 4 and 5 show emission spectra of selected white emitting LEDs with the blue pumping LEDs, LED 1 for FIG. 4 and LED 2 for FIG. 5, respectively.

(18) It can be shown that with the material according to Example I several LEDs with low CCT and excellent colour rendering indices R.sub.a and high colour rendering index R.sub.9 could be fabricated. R.sub.9 is a measured for the reproduction of saturated red colours. The data are shown in Table I and II, whereby Table I refers to the spectra of FIG. 4 and Table II refers to the spectra of FIG. 5.

(19) TABLE-US-00001 TABLE I CCT 4411 3583 3323 3286 3256 3231 3210 [K] Ra 82 76 73 73 73 73 72 uv 0.025 0.006 0.004 0.006 0.007 0.008 0.009 x 0.3535 0.3942 0.4207 0.4251 0.4289 0.4323 0.4352 y 0.3116 0.3701 0.4081 0.4144 0.4199 0.4247 0.429 LE 273 307 327 330 333 335 337 [lm/W] R1 87.5 76.8 72.2 71.5 70.9 70.4 70 R2 86.1 81.2 78.1 77.6 77.2 76.9 76.6 R3 77.6 80.9 81.1 81.2 81.3 81.4 81.5 R4 81.7 75.5 73.8 73.5 73.3 73.1 73 R5 85.2 74.2 69.2 68.4 67.8 67.2 66.8 R6 75.7 70.7 66.6 66.1 65.6 65.1 64.8 R7 82.9 82.7 83.9 84.2 84.5 84.8 85.1 R8 81.2 67.9 63 62.3 61.7 61.2 60.8 R9 55.3 17.7 3.2 1 0.7 2.2 3.5 R10 60.4 52 46.4 45.6 44.9 44.3 43.8 R11 78.3 69.8 67.1 66.7 66.3 66 65.7 R12 63.3 49.9 40.3 38.8 37.6 36.5 35.6 R13 85.5 76.6 72 71.4 70.8 70.3 69.9 R14 85.6 88.2 88.6 88.7 88.7 88.8 88.9

(20) TABLE-US-00002 TABLE II CCT 4587 3597 3395 3274 3230 3194 3163 3138 [K] Ra 89 81 79 77 76 76 75 75 uv 0.021 0.006 0 0.003 0.005 0.006 0.007 0.008 x 0.3505 0.3942 0.4109 0.4228 0.4275 0.4316 0.4353 0.4385 y 0.3167 0.3716 0.3927 0.4076 0.4135 0.4187 0.4233 0.4273 LE 275 306 317 324 327 330 332 334 [lm/W] R1 92.1 80.9 77.1 74.6 73.7 72.9 72.2 71.6 R2 94.8 89.4 85.9 83.6 82.7 81.9 81.3 80.7 R3 93.2 91.1 89.6 88.5 88.1 87.7 87.4 87.1 R4 83.1 75.7 73.9 72.8 72.3 72 71.6 71.4 R5 88.7 78.2 74.1 71.3 70.3 69.4 68.6 67.9 R6 85.9 80.6 76.5 73.5 72.4 71.4 70.6 69.8 R7 87.8 86.5 87 87.4 87.6 87.7 87.9 88.1 R8 84.7 69.5 65.8 63.5 62.6 61.8 61.2 60.7 R9 69.4 26.7 15.7 8.6 5.9 3.7 1.7 0.1 R10 87.9 69.6 62.6 57.9 56.2 54.7 53.4 52.3 R11 75.9 67.7 65.6 64.2 63.7 63.2 62.8 62.5 R12 65.6 55.8 48.4 42.9 40.7 38.8 37.2 35.6 R13 94.1 82.9 78.7 76 74.9 74.1 73.3 72.6 R14 95.9 94.3 93.3 92.7 92.5 92.3 92.1 92

(21) FIG. 6 shows a diagram of the x-y-color coordinates (CIE 1931) against the temperature of a luminescent material according to Example I of the present invention. In this Figure it can be clearly seen that the x-y-color point stays nearly constant with temperature, which leads to an excellent color stability for a wide range of illumination systems according to the present invention.

(22) The particular combinations of elements and features in the above detailed embodiments are exemplary only; the interchanging and substitution of these teachings with other teachings in this and the patents/applications incorporated by reference are also expressly contemplated. As those skilled in the art will recognize, variations, modifications, and other implementations of what is described herein can occur to those of ordinary skill in the art without departing from the spirit and the scope of the invention as claimed. Accordingly, the foregoing description is by way of example only and is not intended as limiting. The invention's scope is defined in the following claims and the equivalents thereto. Furthermore, reference signs used in the description and claims do not limit the scope of the invention as claimed.