Phosphor Converted LED

Abstract

The invention provides a lighting device configured to provide white lighting device light, the lighting device comprising (i) a light source, configured to provide blue light source light, and (ii) a luminescent material element, configured to absorb at least part of the blue light source light and to convert into luminescent material light, wherein the luminescent material element comprises a luminescent material which consists for at least 80 wt. % of a M.sub.2-2xEu.sub.2xSi.sub.5-yAl.sub.yO.sub.yN.sub.8-y phosphor, wherein M comprises one or more of Mg, Ca, Sr, Ba, with a molar ratio of (Mg+Ca+Sr)/(Ba)≦0.1, wherein x is in the range of 0.001-0.02, wherein y is in the range of ≦0.2, and wherein the white lighting device light comprises said blue light source light and said luminescent material light.

Claims

1. A lighting device configured to provide white lighting device light the lighting device comprising (i) a light source configured to provide blue light source light, and (ii) a luminescent material element, configured to absorb at least part of the blue light source light and to convert into luminescent material light with a peak emission wavelength in the range of 570-580 nm, wherein the luminescent material element comprises a luminescent material which consists for at least 80 wt. % of a M.sub.2-2xEu.sub.2xSi.sub.5-yAl.sub.yO.sub.yN.sub.8-y phosphor, wherein M comprises one or more of Mg, Ca, Sr, Ba, with a molar ratio of (Mg+Ca+Sr)/(Ba)≦0.1, wherein x is in the range of 0.001-0.01, wherein y is in the range of ≦0.2, wherein an emission of the M.sub.2-2xEu.sub.2xSi.sub.5-yAl.sub.yO.sub.yN.sub.8-y phosphor has a full width half maximum (FWHM) of 2200 cm.sup.−1 or less, and wherein the white lighting device light comprises said blue light source light and said luminescent material light.

2. The lighting device according to claim 1, wherein (Mg+Ca+Sr)/(Ba)≦0.05.

3. The lighting device according to claim 1, wherein (Mg+Ca+Sr)/(Ba)≦0.01.

4. The lighting device according to claim 1, wherein y is in the range of ≦0.02.

5. The lighting device according to claim 1, wherein the light source comprises a solid state light source with a light emitting surface.

6. The lighting device according to claim 5, wherein the light source is configured to provide having a dominant wavelength in the range of 435-470 nm.

7. The lighting device according to claim 5, wherein the light source is configured to provide having a dominant wavelength in the range of 445-460 nm.

8. The lighting device according to claim 5, wherein the luminescent material element is in physical contact with the light emitting surface of the solid state light source.

9. The lighting device according to claim 1, wherein the luminescent material element comprises a transparent material with the luminescent material embedded therein.

10. The lighting device according to claim 1, wherein the luminescent material element comprises a silicone matrix with the luminescent material embedded therein.

11. The lighting device according to claim 1, wherein the luminescent material comprises for less than 20 wt. % of a second phosphor selected from the group of cerium comprising garnet materials.

12. The lighting device according to claim 1, wherein the phosphor is obtainable by heating of a mixture of Eu.sub.2Si.sub.5N.sub.8, BaH.sub.2 and Si.sub.3N.sub.4 at a temperature in the range of 1550-1800° C. under a neutral or reducing atmosphere.

13. Use of the lighting device according to claim 1, in a decorative lighting application or a signal lighting application.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] 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 FIG. 1 schematically depicts an embodiment of the lighting device. The drawing is not necessarily on scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] FIG. 1 schematically depicts an embodiment of the lighting device indicated with reference 100. The lighting device 100 is especially configured to provide white lighting device light 101. The lighting device 100 comprises a light source 10 which is configured to provide blue light source light 11. Further, the lighting device 100 comprises a luminescent material element 20 which is configured, especially the phosphor or luminescent material 30, to absorb at least part of the blue light source light 11 and which is configured to convert into luminescent material light 21. The luminescent material element 20 is configured downstream of the light source 10 (especially its light emitting surface, see below). Further, the luminescent material element is in this embodiment transmissive for at least part of the light source light 11. Note that the luminescent material element 20 may (thus) have waveguiding properties. The white lighting device 101 light comprises said blue light source light 11 and said luminescent material light 21. Especially, the light source 10 may comprise a solid state light source 1010 with a light emitting surface 1012, also known as die. Reference 30 indicates the luminescent material comprises by the luminescent material element. This luminescent material 30 especially provides the luminescent material light 21. Here, by way of example the luminescent material 30 is indicated as particles or regions. However, often the luminescent material 30 is homogeneously distributed over the luminescent material element. The luminescent material or phosphor 30 consists for at least 80 wt. % of a M.sub.2-2xEu.sub.2xSi.sub.5-yAl.sub.yO.sub.yN.sub.8-y phosphor 130, which provides the herein indicated yellow light. Note that such phosphor may have an emission band extending also in e.g. the red. Hence, reference 130 indicates the M.sub.2-2xEu.sub.2xSi.sub.5-yAl.sub.yO.sub.yN.sub.8-y phosphor, and reference 30 indicates the luminescent material in general, which may optionally comprise for 20 wt. % or less of a second phosphor (second phosphors).

[0039] The distance between the luminescent material 30, or here the luminescent material element 20, and the light source 10, especially its light emitting surface 1012 is indicated with d1, which is in this embodiment larger than 0 mm, but which could also be practically 0 mm, i.e. in physical contact. The thickness of the luminescent material element 20 is herein indicated with reference d2. For instance, the thickness may be in the range of a 5 μm up to 10 mm, like 10 μm u 5 mm. The thickness may depend upon the type of application, with the thinner layer thicknesses especially relevant for the non-remote or vicinity applications, and the larger layer thicknesses d2 especially relevant for remote applications.

Example 1: Phosphor Powder Preparation

[0040] It was found most suitable if the yellow emitting Ba.sub.2Si.sub.5N.sub.8:Eu phosphor is produced by the following method: 57.7721 g (414.59 mmol) BaH.sub.2, 1.1651 g (2.09 mmol) Eu.sub.2Si.sub.5N.sub.8 (prepared by carbon reduction of a graphite, Eu(III) oxide and silicon nitride mixture at 1450° C. under nitrogen) and 46.9985 g (335.03 mmol) Si.sub.3N.sub.4 (alpha phase content >90%) are mixed by ball milling and fired at 1690° C. for 8 hrs in molybdenum crucibles under nitrogen atmosphere. After milling and washing with hydrochloric acid (5N), water and ethanol, Ba.sub.1.98Si.sub.5N.sub.8:Eu.sub.0.02 phosphor powder is obtained. XRD analysis shows that the material crystallizes in the orthorhombic M.sub.2Si.sub.5N.sub.8 lattice type with lattice constants a.sub.0=5.7803 Å, b.sub.0=6.9506 Å, c.sub.0=9.3855 Å. Emission measurements show a peak emission at 575 nm and FWHM=2050 cm.sup.−1 for 440 nm excitation.

Example 2: LED Fabrication

[0041] The phosphor powder of example 1 is mixed with silicone (6 wt %) at 3000 rpm for 30 sec and dispensed into 3535 type mid power LED packages. The following table shows data obtained at 65 mA drive current at room temperature.

TABLE-US-00001 Centr. Dom. wavelength wavelength LE sample x y u′ v′ [nm] [nm] [lm/W] flux (lm) 2495 0.4536 0.3995 0.2635 0.5221 575.0 585.5 407 32.00 2496 0.4619 0.4086 0.2647 0.5269 577.5 584.7 413 32.18 2497 0.4588 0.4051 0.2643 0.5251 576.6 585.0 410 31.94

[0042] These data show the unexpected advantage that only a very narrow emission band of the BSNE phosphor can lead to single phosphor white emission if combined with a blue pump LED in the low CCT range.

Example 3: Emission Behavior

[0043] A plurality of phosphors was made with different Eu concentrations. The concentrations of Ba, Mg, Ca and Sr was also varied. For a number of variants, the ratio of the earth alkali cations was kept constant, and only the Eu concentration was varied. The following was found:

Peak emission for zero layer thickness*=a+b[Eu]+c[Eu].sup.2+d[Sr]+e[Sr].sup.2+f[Ca]+g[Ca].sup.2

With (values in %)

TABLE-US-00002 a b c d 571.6972251 6.848095774 −0.447874237 0.706530585 e f g −0.004088736 −0.030072156 0.032754792

[0044] Hence, ˜572 nm is thus the shortest wavelength of the “258” or “BSNE” phosphors. Herebelow, optical data for infinitely thin layers obtained by extrapolation from a powder in silicone layer thickness series of two samples are discussed in more detail: *peak position is calculated from a series of phosphor layers of varying optical thickness, the zero layer value corresponds well with the spectrum found for the LEDs

TABLE-US-00003 λ centroid λ peak λ dominant FWHM FWHM sample (nm) (nm) (nm) (nm) (cm.sup.−1) 2% Eu 596.8 578.5 582 71.9 2106 (i.e. x = 0.02) 1% Eu 589.1 575.1 579 68.8 2050 (i.e. x = 0.01)

[0045] In this table, the centroid wavelength, the peak wavelength, and the dominant wavelength are indicated, as well as the full width half maximum in nanometers and reciproke centimeters.

[0046] Best results seem obtainable with a luminescent material element with over 95% wt. % of the BSNE phosphor, having a value of x in the range of 0.005-0.015, especially 0.008-0.012, directly arranged on the LED die, and with the luminescent material having a number averaged particle size in the range of 6-17 μm, especially in the range of 10-14 μm, and especially embedded in a matrix, more especially a silicone matrix.