PC-LED MODULE WITH ENHANCED WHITE RENDERING AND CONVERSION EFFICIENCY

Abstract

The invention provides a lighting device (100) comprising: a first solid state light source (10), configured to provide UV radiation (11) having a wavelength selected from the range of 380-420 nm; a second solid state light source (20), configured to provide blue light (21) having a wavelength selected from the range of 440-470 nm; a wavelength converter element (200), wherein the wavelength converter element (200) comprises: a first luminescent material (210), configured to provide upon excitation with the blue light (21) of the second solid state light source (20) first luminescent material light (211) having a wavelength selected from the green and yellow wavelength range, and wherein the first luminescent material excitability for UV radiation (11) is lower than for blue light (21); and a second luminescent material (220), configured to provide upon excitation with the blue light (21) of the second solid state light source (20) second luminescent material light (221) having a wavelength selected from the orange and red wavelength range, and wherein the second luminescent material excitability for UV radiation (11) is lowerthan for blue light (21).

Claims

1. A lighting device comprising: a first solid state light source, configured to provide UV radiation having a wavelength selected from the range of 380-420 nm; a second solid state light source, configured to provide blue light having a wavelength selected from the range of 440-470 nm; a wavelength converter element, wherein the wavelength converter element comprises: a first luminescent material, configured to provide upon excitation with the blue light of the second solid state light source first luminescent material light having a wavelength selected from the green and yellow wavelength range, and wherein the first luminescent material excitability for UV radiation is lower than for blue light; and a second luminescent material, configured to provide upon excitation with the blue light of the second solid state light source second luminescent material light having a wavelength selected from the orange and red wavelength range, and wherein the second luminescent material excitability for UV radiation is lower than for blue light; wherein the lighting device is configured to provide lighting device light which comprises said UV radiation, said blue light, said first luminescent material light and said second luminescent material light.

2. The lighting device according to claim 1, wherein the first luminescent material is selected from the group consisting of the A3B5O12:Ce3+ class, the MA2O4:Ce3+ class, the MS:Ce3+ class, and the A3Z6N11:Ce3+ class, wherein A is selected from the group of lanthanides, scandium, yttrium and lanthanum, wherein B is selected from the group of aluminum and gallium, wherein M is selected from the group of earth alkaline elements, and wherein Z is selected from the group of silicon and germanium.

3. The lighting device according to any claim 1, wherein the second luminescent material is selected from the group of the MD:Eu class, the MGB3N4:Eu class, the M′B2M″2N4:Eu class, the MM″3ZN4:Eu class and the G2ZF6:Mn class, wherein M is selected from the group of earth alkaline elements, wherein M′ is selected from the group of Sr, Ba and Ca, wherein M″ is selected from the group of Be, Mg, Mn, Zn and Cd, wherein D is selected from the group of S and Se, wherein Z is selected from the group of Si, Ge, Ti, Zr, Hf, Sn and wherein G is selected from the group of alkaline elements.

4. The lighting device according to claim 1, wherein the first luminescent material comprises A.sub.3B.sub.5O.sub.12:Ce.sup.3+, wherein A is selected from the group consisting of Sc, Y, Tb, Gd, and Lu, and wherein B is selected from the group consisting of Al and Ga.

5. The lighting device according to claim 1, wherein the second luminescent material comprises:
M.sub.1-x-y-zZ.sub.zA.sub.aB.sub.bC.sub.cD.sub.dE.sub.eN4−nO.sub.n:ES.sub.x,RE.sub.y   (I) with M=selected from the group consisting of Ca, Sr, and Ba Z=selected from the group consisting of monovalent Na, K, and Rb A=selected from the group consisting of divalent Mg, Mn, Zn, and Cd B=selected from the group consisting of trivalent B, Al and Ga C=selected from the group consisting of tetravalent Si, Ge, Ti, and Hf D=selected from the group consisting of monovalent Li, and Cu E=selected for the group consisting of P, V, Nb, and Ta 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 0≦x0.2; 0≦y≦0.2; 0<x+y≦0.4; 0≦z<1; 0≦n≦0.5; 0≦a≦4;0≦c≦4;0≦d≦4;0≦e≦4; a+b+c+d+e=4; and 2a+3b+4c+d+5e=10−y−n+z.

6. The lighting device according to claim 1, wherein the first luminescent material is selected from the group consisting of (Y,Gd,Lu)3(Al,Ga)5O12:Ce3+, CaSc2O4:Ce3+, CaS:Ce3+ and La3Si6N11:Ce3+, and wherein the second luminescent material is selected from the group of (Sr,Ba,Ca)(Se,S):Eu, SrLiAl3N4:Eu, CaBe3SiN4:Eu, SrAl2Mg2N4:Eu, and K2SiF6:Mn.

7. The lighting device according to claim 1, wherein the wavelength converter element is configured at a non-zero distance from the first solid state light source and the second solid state light source.

8. The lighting device according to claim 1, wherein the wavelength converter element is configured as window of a mixing chamber, wherein the first solid state light source and the second solid state light source are configured to provide their solid state light source light in the mixing chamber, and wherein the solid state light sources and the wavelength converter element are configured to provide lighting device light downstream from the wavelength converter element, wherein lighting device light comprises white light or wherein the lighting device is controllable to provide lighting device light being white light.

9. The lighting device according to claim 1, wherein the wavelength converter element comprises a matrix where in the first luminescent material and the second luminescent material are embedded.

10. The lighting device according to claim 1, wherein the wavelength converter element comprises a support comprising one or more coatings, wherein one or more of the coatings comprise one or more of the first luminescent material and the second luminescent material.

11. The lighting device according to claim 1, wherein the lighting device does not comprise a diffuser element arranged downstream from the wavelength converter element.

12. The lighting device according to claim 1, wherein the power of the second solid state light source is equal to or larger than 80% of the total power of the first solid state light source and second solid state light source. wherein the number of second solid state light sources is larger than 4 times the number of first solid state light sources.

13. The lighting device according to claim 1, wherein the absorption ratio ABS.sub.460/ABS.sub.410 is at least 1.5 for the first luminescent material and wherein the absorption ratio and ABS.sub.460/ABS.sub.410 is at least 1.1 for the second luminescent material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0085] 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:

[0086] FIGS. 1a-1b schematically depict some embodiments of the lighting device as described herein; and

[0087] FIGS. 2a-2c show reflection and luminescence of some of the possible luminescent materials, also in relation to alternative solutions, respectively.

[0088] The schematic drawings are not necessarily on scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0089] FIGS. 1a and 1b schematically depict a lighting device 100 comprising a first solid state light source 10, configured to provide UV radiation 11 having a wavelength selected from the range of 380-420 nm and a second solid state light source 20, configured to provide blue light 21 having a wavelength selected from the range of 440-470 mn. Further, the device 100 comprises a wavelength converter element 200. The wavelength converter element 200 comprises a first luminescent material 210, configured to provide upon excitation with the blue light 21 of the second solid state light source 20 first luminescent material light 211 having a wavelength selected from the green and yellow wavelength range, and a second luminescent material 220, configured to provide upon excitation with the blue light 21 of the second solid state light source 20 second luminescent material light 221 having a wavelength selected from the orange and red wavelength range.

[0090] As indicated above, the first luminescent material excitability for UV radiation 11 is lower than for blue light 21, and the second luminescent material excitability for UV radiation 11 is lower than for blue light 21 (see also examples below).

[0091] In both schematically depicted embodiments the wavelength converter element 200 is configured at a non-zero distance (d) from the first solid state light source 10 and the second solid state light source 20. Distance d may e.g. be in the range of 0.1-100 mm, such as especially 1-50 mm, like 5 -50 mm.

[0092] In both embodiments, by way of example the wavelength converter element 200 is configured as window 210 of a mixing chamber 120.

[0093] In another embodiment, not depicted, the solid state light sources are fully embedded within a matrix material, which contains the wavelength converter materials. The wavelength converter materials can be homogeneously distributed within the matrix or form a homogeneous layer, as it can be generated by sedimentation of a powder in the matrix.

[0094] The lighting device provides light 201 downstream from the wavelength converter element 200. In embodiments, the lighting device light 201 is white light. Optionally a controller 50 may be configured to control the lighting device light. Hence, the lighting device 100 may be controllable to provide lighting device light 201 being white light or colored light. In this way also the color temperature may be controlled. Especially, controllability of the device light 201 may be improved by adding one or more other light sources, especially configured to emit at other wavelength ranges than the first solid state light source 210 and the second solid state light source 220. Especially, such further light source, especially further solid state light source, is configured to provide (solid state) light source light at wavelengths where at least one of the luminescent materials 210,220 does not (substantially) absorb. Hence, the dominant wavelength of the light source light of such further light source especially differs from the dominant wavelengths of the first light source and the second light source, respectively, and may even especially differ from the dominant wavelengths of the first luminescent material emission and the second luminescent material emission, respectively.

[0095] In FIG. 1a, the wavelength converter element 200 comprises a matrix 230 where in the first luminescent material 210 and the second luminescent material (220) are embedded. This may be particulate luminescent material, embedded in e.g. a polymer, such as a polymer selected from the group PE (polyethylene), PP (polypropylene), PEN (polyethylene napthalate), PC (polycarbonate), polymethylacrylate (PMA), polymethylmethacrylate (PMMA) (Plexiglas or Perspex), cellulose acetate butyrate (CAB), polyvinylchloride (PVC), polyethylene terephthalate (PET), (PETG) (glycol modified polyethylene terephthalate), PDMS (polydimethylsiloxane), and COC (cyclo olefin copolymer). However, in another embodiment matrix may comprise an inorganic material. Preferred inorganic materials are selected from the group consisting of glasses, (fused) quartz, transmissive ceramic materials, and silicones. Also hybrid materials, comprising both inorganic and organic parts may be applied. Especially preferred are PMMA, transparent PC, silicone, or glass as material for the matrix. Especially, silicone may be of interest, but also PDMS and polysilsesquioxane. In this way, the converter element may also be used as waveguide.

[0096] In FIG. 1b, the wavelength converter element 200 comprises a support 240 comprising one or more coatings 241, wherein one or more of the coatings comprise one or more of the first luminescent material 210 and the second luminescent material 220. Note that the support 240 may optionally be the matrix of the above embodiment. Here, by way of example the coatings 241 are provided at the downstream side of the support 240. However, alternatively or additionally one or more coatings may be provided at the upstream side of the support 240. Further, by way of example the first coating 241a comprises the first luminescent material 210 and a second coating 241b comprises the second luminescent material 220.

[0097] To realize the claimed LED system phosphor systems need to be selected that show strongest light absorption in the blue spectral range and only low absorption in the violet spectral range. Well-known and widely applied green to yellow emitting phosphors are Ce(III) doped garnet materials such as Lu.sub.3Al.sub.5O.sub.12:Ce (LuAg) or Y.sub.3Al.sub.5O.sub.12:Ce (YAG). Alternative material systems that are commercially available from Mitsubishi Chemical Company are e.g. Cc(III) doped Scandates such as CaSc.sub.2O.sub.4:Cc (green) or Cc(III) doped nitrides such as La.sub.3Si.sub.6N.sub.11:Ce (yellow). For the red spectral range Eu(II) doped phosphors that combine a high symmetry dopant site (octahedral or cubic coordination) with a strong ligand field. Examples are alkaline earth sulfides such as SrS:Eu or Ca(Se,S):Eu or nitrides of composition SrLiAl.sub.3N.sub.4:Eu or SrAl.sub.2Mg.sub.2N.sub.4:Eu. Other options for red phosphors are Mn(IV) doped fluoride materials such as K2SiF.sub.6:Mn that show narrow absorption bands in the blue spectral range due to promotion of a 3d electron of the octahedral .sup.4A.sub.2 state into the .sup.4T.sub.2 state.

[0098] Especially, the LED system comprises a combination of Lu.sub.3Al.sub.5O.sub.12:Ce (LuAg) or Y.sub.3Al.sub.5O.sub.12:Ce (YAG) for green and yellow emitting phosphors and SrLiAl.sub.3N.sub.4:Eu as red phosphors. The combination of these phosphors is especially efficient under high operating temperatures that are typically reached in LED modules used e.g. for spot lighting due to the high flux densities required. FIG. 2a shows thick powder bed reflectance spectra of the preferred materials of the invention. The materials show significantly stronger absorption in the blue spectral range than in the violet spectral range while e.g. a red phosphor material such as CaSiAlN3:Eu shows strong absorption in the violet spectral range (not shown). In order to reach the desired conversion efficiency gains phosphor systems suitable for the current invention should absorption (ABS=1−REF) rations for 460 nm and 410 nm excitation of at least ABS.sub.460/ABS.sub.410>1.6 for green to yellow emitting phosphors and ABS.sub.460/ABS.sub.410>1.17 for red emitting phosphors for reflectance spectra of optically infinitely thick powder samples measured in air at room temperature.

EXAMPLES

[0099] FIG. 2a shows the thick powder layer reflectance spectra of Ca(0.7 Se, 0.3 S):Eu (1); (0.25 Ca, 0.75 Sr)S:Eu (2); CaS:Eu (3); K2SiF6:Mn (4); SrLiAl3N4:Eu (5); Lu3Al5O12:Ce (6); and Y3Al5O12:Ce (7) (reflection on y-axis as function of the wavelength (nm) on the x-axis).

[0100] A light source comprising 30 blue LED chips emitting at 455 nm and 6 violet LED chips emitting at 415 nm and a phosphor in silicone layer comprising LuAG (GAL515), YAG (NYAG4653) and SrLiAl.sub.3N.sub.4:Eu(0.3%) has been fabricated. The phosphor mixture of the LED module has been adjusted to maximize color rendition in the red spectral range (R9=97, CRI(8)=90) and to increase emission color separation of the yellow and red part (emission dip at ˜600 nm) to improve saturated color rendition similar to similar to prior art solutions. By changing the ratio of e.g. LuAG and YAG phosphors the spectrum can be tuned to e.g. optimize for maximum luminous efficacy or overall color rendition. Table 1 summarizes the performance data of an example of the claimed lighting system. Due to the selection of phosphor that only show weak absorption in the violet spectral range the number of violet LED chips could be reduced and the luminous efficacy further enhanced compared to prior are lighting systems with enhanced whiteness rendition.

[0101] FIG. 2b: shows the emission spectra of the inventive LED system (curve B) and comparison with two alternative available solutions (A and C) (intensity on y-axis in arbitrary units as function of the wavelength (nm) on the x-axis). All correlated color temperatures 3000K. The inventive LED system shows at least four maxima.

TABLE-US-00001 TABLE 1 performance data of inventive LED lighting system LED Int. ratio LE CE system blue/violet u.sup.t v.sup.t [lm/W] [lm/Wopt.] CRI(8) R9 B 85% 0.247 0.516 272 184 90 97 A 60% 0.256 0.518 262 169 97 90 C  0% 0.247 0.518 251 156 97 97 D 88% 0.258 0.525 316 210 93 86 E 79% 0.247 0.519 315 208 94 56 [0102] Example D: CaSc2O4:Ce, YAG:Ce, K2SiF6:Mn [0103] Example E: CaSc2O4:Ce, Ca(Se,S):Eu

[0104] As can be concluded from the table, the efficiency is very high, while also having a good color rendering index CR1 and a good R9 color rendering.

[0105] FIG. 2c shows the emission spectra (intensity on y-axis in arbitrary units as function of the wavelength (nm) on the x-axis) of examples of suitable materials: CaS:Eu (1); Ca0.75Sr0.25:Eu (2); Ca0.5Sr0.5:Eu (3); Ca0.25Sr0.75S:Eu (4); SrS:Eu (5); Ca(S,Se):Eu (6); CaS:Ce (7); K2SiF6:Mn (8); SrLiAl3N4:Eu (9); YAG:Ce (10); Lu3A5O12: Ce (LuAG) (11); Y3(Al,Ga)5O12:Ce (12); Lu3(Al,Ga)5O12:Ce (13); (Lu,Y)3Al5O12:Ce (14).