Light source comprising a luminescent substance and associated illumination unit

Abstract

A light source includes a primary radiation source, which emits radiation in the shortwave range of the optical spectral range, wherein this radiation is converted at least by means of a first luminescent substance entirely or partially into secondary longer-wave radiation in the visible spectral range, wherein the first luminescent substance originates from the class of nitridic modified orthosilicates (NOS), wherein the luminescent substance has as a component M predominantly the group EA=Sr, Ba, Ca, or Mg alone or in combination, wherein the activating dopant D is composed at least of Eu and replaces a proportion of M, and wherein a proportion of SiO2 is introduced in deficiency, so that a modified sub-stoichiometric orthosilicate is provided, wherein the orthosilicate is an orthosilicate stabilized with RE and N, where RE=rare earth metal.

Claims

1. A light source comprising a primary radiation source, which emits radiation in the shortwave range of the optical spectral range in the wavelength range of 420 to 480 nm, wherein this radiation is converted at least by means of a first luminescent substance entirely or partially into secondary longer-wave radiation in the visible spectral range, wherein the first luminescent substance belongs to a class of nitridic modified orthosilicates (NOS), wherein a batch stoichiometry corresponds to a formula EA.sub.2-x-aRE.sub.xEu.sub.aSi.sub.1-yO.sub.4-x-2yN.sub.x, wherein EA=Sr, Ba, Ca, or Mg alone or in combination, RE=La or Lu or Dy or Yb alone or in combination, x is between 0.002 and 0.02, a is between 0.01 and 0.20, 0<y≦0.1 and wherein the full width at half maximum (FWHM) of the NOS is at most 90 nm.

2. The light source as claimed in claim 1, wherein EA contains Sr, Ba or a mixture of Sr and Ba with at least 66 mol-%.

3. The light source as claimed in claim 2, wherein EA is a mixture of Sr and Ba with Sr/Ba=0.8 to 1.2.

4. The light source as claimed in claim 2, wherein EA is a mixture of Sr and Ba with Sr/Ba=0.9 to 1.1.

5. The light source as claimed in claim 1, wherein the primary radiation source emits a blue radiation in a wavelength range of 440 to 470 nm, wherein this radiation is partially converted by means of the first luminescent substance into secondary green radiation in the visible spectral range, having peak emission in the range of 510 to 540 nm.

6. The light source as claimed in claim 5, wherein a part of the primary radiation is converted by means of further luminescent substances into longer-wave radiation, wherein at least one of the further luminescent substances has a FWHM of at most 90 nm.

7. The light source as claimed in claim 1, wherein a second luminescent substance is arranged upstream from the primary radiation source, which emits in red and is represented by the formula AEAlSiN.sub.3:Eu, where AE=Ca or Sr, alone or in combination.

8. An illumination unit for LCD backlighting, wherein a light source according to claim 1 is used together with at least one color filter, wherein the light source and the color filter or the conversion LED and the color filter are adapted to one another such that a predefined color space is covered by at least 85% by the radiation emitted from the illumination unit, wherein the color space is in particular NTSC.

9. An illumination unit for LCD backlighting, wherein a light source according to claim 1 is used together with at least one color filter for the red spectral range having a maximum in the range of 625 to 655 nm.

10. The illumination unit for LCD backlighting as claimed in claim 9, wherein the light source or the conversion LED is used together with a color filter for the green spectral range having a maximum in the range of 515 to 535 nm.

11. The illumination unit for LCD backlighting as claimed in claim 9, wherein the light source or the conversion LED is used together with a color filter for the blue spectral range having a maximum between 435-455 nm.

12. The light source as claimed in claim 1, wherein 0.002≦y≦0.02.

13. A conversion LED comprising a chip which emits primary radiation, and a layer containing at least one luminescent substance, which is connected upstream from the chip, and which converts at least a part of the primary radiation of the chip into secondary radiation, the at least one luminescent substance belonging to a class of nitridic modified orthosilicates (NOS), which is derived from the structure M.sub.2SiO.sub.4:D, wherein a batch stoichiometry of the luminescent substance corresponds to the formula EA.sub.2-x-aRE.sub.xEu.sub.aSi.sub.1-yO.sub.4-x-2yN.sub.x, wherein EA=Sr, Ba, Ca or Mg alone or in combination, RE=La or Lu or Dy or Yb alone or in combination, x is between 0.002 and 0.02, a is between 0.01 and 0.20, 0<y≦0.1 and wherein the full width at half maximum (FWHM) of the NOS is at most 90 nm.

14. The conversion LED as claimed in claim 13 wherein CaAlSiN.sub.3:Eu is used as a further luminescent substance.

15. The conversion LED as claimed in claim 13, wherein the layer containing the luminescent substance is cast resin, silicone, or glass.

16. The conversion LED as claimed in claim 13 wherein the layer containing the luminescent substance is cast resin, wherein SiO.sub.2 is used as a filler.

17. An illumination unit for LCD backlighting, wherein a conversion LED according to claim 13 is used together with at least one color filter for the red spectral range having a maximum in the range of 625 to 655 nm.

18. An illumination unit for LCD backlighting, wherein a conversion LED according to claim 13 is used together with at least one color filter, wherein the light source and the color filter or the conversion LED and the color filter are adapted to one another such that a predefined color space is covered by at least 85% by the radiation emitted from the illumination unit, wherein the color space is in particular NTSC.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the disclosed embodiments. In the following description, various embodiments described with reference to the following drawings, in which:

(2) FIG. 1 shows a conversion LED;

(3) FIG. 2 shows an LED module having remotely applied luminescent substance mixture;

(4) FIG. 3 shows an emission spectrum of an LCD backlight LED having a mixture of a green luminescent substance of the type (Sr, Ba).sub.2Si.sub.1-yO.sub.4-x-2yN.sub.x:Eu, Lu and a red luminescent substance of the type aluminum nitrido-silicate CaAlSiN.sub.3:Eu.sup.2+;

(5) FIG. 4 shows a comparison of the color space NTSC and the color space spanned by an LED according to FIG. 3;

(6) FIG. 5 shows a comparison of the color space spanned by various doped LEDs in relation to the color space NTSC;

(7) FIG. 6 shows the efficiency of various luminescent substances in the operation of an LED under low current and high current conditions;

(8) FIG. 7 shows the efficiency loss after 1000 hours of a Lu-doped NOS under harsh conditions, which require chemical stability;

(9) FIG. 8 shows the efficiency loss after 1000 hours of an Yb-doped NOS under harsh conditions, which require chemical stability;

(10) FIG. 9 shows the efficiency loss after 1000 hours of a Dy-doped NOS under harsh conditions, which require chemical stability;

(11) FIG. 10 shows the efficiency loss after 1000 hours of a La-doped NOS under harsh conditions, which require chemical stability;

(12) FIG. 11 shows the efficiency loss after 1000 hours of a slightly La-doped NOS under harsh conditions, which require chemical stability;

(13) FIG. 12 shows the illustration of various color spaces with incorporation of NTSC;

(14) FIG. 13 shows an illustration of a lamp having luminescent substance; and

(15) FIGS. 14A and 14B show illustrations of the influence of SiO.sub.2 on the stabilization of the colorimetric locus.

DETAILED DESCRIPTION

(16) The following detailed description refers to the accompanying drawing that show, by way of illustration, specific details and embodiments in which the disclosure may be practiced.

(17) FIG. 1 shows the construction of a conversion LED for white light on an RGB basis as known per se. The light source is a semiconductor component having a blue-emitting chip 1 of the type InGaN having a peak emission wavelength of 435 to 455 nm peak wavelength, for example, 445 nm, which is embedded in a light-opaque main housing 8 in the region of a recess 9. The chip 1 is connected via a bond wire 14 to a first terminal 3 and directly to a second electrical terminal 2. The recess 9 is filled with a casting compound 5, which contains as the main components a silicone (60-90 wt.-%) and luminescent substances 6 (approximately 15 to 40 wt.-%). A first luminescent substance is a green-emitting nitrido-orthosilicate luminescent substance AE.sub.2-x-aRE.sub.xEu.sub.aSi.sub.1-yO.sub.4-x-2yN.sub.x, where AE is Ba, Sr and RE is Lu. Other exemplary embodiments use at least one of the following elements: for AE=Ba, Sr, Ca, Mg and for RE=Dy, Yb, La. In addition, a red-emitting luminescent substance, for example, an aluminum nitrido-silicate or calsin is used as a second luminescent substance. The recess has a wall 17, which is used as a reflector for the primary and secondary radiation from the chip 1 or the luminescent substance 6. Specific exemplary embodiments for further luminescent substances are, for generating white, a CaAlSiN.sub.3:Eu modified by copper or oxygen or a (Ca, Sr) AlSiN.sub.3:Eu.

(18) In principle, the use of the luminescent substance mixture as a dispersion, as a thin film, etc., directly on the LED or also, as is known per se, on a separate carrier connected upstream from the LED is possible.

(19) An illumination unit furthermore also comprises a green color filter 45, a red color filter 46, and optionally a blue color filter 47, which are mounted upstream from the LED.

(20) FIG. 2 shows such a module 20 having diverse LEDs 24 on a base plate 21. A housing is installed over them, having side walls 22 and a cover plate 23. The luminescent substance mixture is applied here as a layer 25 to both the side walls and also above all to the cover plate 23, which is transparent.

(21) Other suitable light sources are luminescent substance lamps or high-pressure discharge lamps, in which the novel luminescent substance can be used for conversion of the primary radiation, alone or in combination with other luminescent substances. These luminescent substances are typically applied to the wall of a bulb of the lamp.

(22) FIG. 3 shows the spectrum of a converted LCD backlight LED on the basis of two luminescent substances. The excitation is performed by a primary emitting LED having 448 nm peak wavelength (blue). The wavelength is plotted in nanometers on the abscissa and the relative emission intensity is plotted on the ordinate. A first introduced luminescent substance is a red luminescent substance of the type CaAlSiN.sub.3:Eu, the second is a green luminescent substance according to the present disclosure having the batch stoichiometry (Ba, Sr).sub.2-x-aLu.sub.xEu.sub.aSi.sub.1-yO.sub.4-x-2yN.sub.x, where x=0.005, a=0.08, and y=0.0075.

(23) The production of the novel sub-stoichiometric luminescent substance is performed in the following manner:

(24) The educts analogous to the batch mixtures 1 to 4 are weighed and homogenized, preferably together with a suitable flux. Subsequently, the educt mixture is annealed for several hours under reducing atmosphere (in particular under N.sub.2 or Ar or a mixture of N.sub.2/H.sub.2 or Ar/H.sub.2) at temperatures between 1000° C. and 1500° C. A secondary annealing can then be performed, also under reducing atmosphere (in particular under N.sub.2 or Ar or a mixture of N.sub.2/H.sub.2 or Ar/H.sub.2) at temperatures between 800° C. and 1400° C. The synthesis is carried out in a suitable furnace, e.g., tube furnaces or chamber furnaces.

(25) a) comparative example/batch mixture 1 (prior art):

(26) 73.5 g SrCO.sub.3, 98.1 g BaCO.sub.3, 31.1 g SiO.sub.2, and 7.2 g Eu.sub.2O.sub.3;

(27) b) comparative example/batch mixture 2 (prior art):

(28) 73.3 g SrCO.sub.3, 97.9 g BaCO.sub.3, 31.1 g SiO.sub.2, 0.4 g LaN, and 7.2 g Eu.sub.2O.sub.3;

(29) c) embodiment/batch mixture 3:

(30) 73.4 g SrCO.sub.3, 98.0 g BaCO.sub.3, 30.8 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.4 g La.sub.2O.sub.3, and 7.2 g Eu.sub.2O.sub.3;

(31) d) embodiment/batch mixture 4:

(32) 73.3 g SrCO.sub.3, 98.0 g BaCO.sub.3, 30.9 g SiO.sub.2, 0.4 g LaN, and 7.2 g Eu.sub.2O.sub.3.

(33) A significant improvement of the LED stability can already be recognized at higher temperatures and in a damp environment due to the incorporation of lanthanum and nitrogen in comparative example 2. For many applications, for example, for LCD backlighting, this stability is still not always optimal, however.

(34) The novel batch stoichiometry described here according to exemplary embodiment 3 or 4 having a corresponding deficiency of SiO.sub.2 has been proven to result in improved LED stability, above all in a damp environment and at higher temperatures. FIG. 5 shows the LED stability at a temperature of 45° C. and 95% ambient humidity for the four different batch mixtures. The relative conversion ratio is plotted as the ordinate, and the abscissa is the time in minutes. It is shown that embodiments 3 and 4 are approximately equivalent to one another and both are markedly superior to comparative examples 1 and 2.

(35) The relative quantum efficiencies QE.sub.460 of the novel luminescent substances according to embodiments 3 and 4 upon excitation at 460 nm is 3% higher than in comparative example 2. The preparation of the described nitrido-orthosilicates of the form AE.sub.2-x-aRE.sub.xEu.sub.aSi.sub.1-yO.sub.4-x-2yN.sub.x, is typically performed from AECO.sub.3, SiO.sub.2, REN, and Eu.sub.2O.sub.3 or AECO.sub.3, SiO.sub.2, Si.sub.3N.sub.4, (RE).sub.2O.sub.3, and Eu.sub.2O.sub.3 as starting substances. In the latter, the rare earths are used as (RE).sub.2O.sub.3, if trivalent oxides are preferably formed. In the case of rare earth oxides which are preferably provided as mixed oxides, for example, Tb is typically provided as a III/IV mixed oxide Tb.sub.4O.sub.7, the mixed oxides are preferably used. Furthermore, instead of REN or RE oxide in conjunction with Si.sub.3N.sub.4, In, Y, or Sc can also be used as a nitride or as a combination of oxide and Si.sub.3N.sub.4.

(36) Furthermore, in particular fluorides and chlorides, such as AECl.sub.2 or RECL.sub.2, AEF.sub.2 or RECL.sub.2, but also NH.sub.4Cl/NH.sub.4F, H.sub.3BO.sub.3, LiF, and cryolites, and also combinations thereof, can be used as fluxes.

(37) The educts analogous to the batch mixtures 1 to are weighed and homogenized, together with a suitable flux. Subsequently, the educt mixture is annealed for several hours under reducing atmosphere (e.g. under N.sub.2 or Ar or a mixture of N.sub.2/H.sub.2 or Ar/H.sub.2) at temperatures between 1000° C. and 1500° C. A secondary annealing can then be performed, also under reducing atmosphere (e.g. under N.sub.2 or Ar or a mixture of N.sub.2/H.sub.2 or Ar/H.sub.2) at temperatures between 800° C. and 1400° C. The synthesis is carried out in a suitable furnace, e.g., tube furnaces or chamber furnaces.

(38) Batch mixture 1:

(39) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.5 g La.sub.2O.sub.3, and 7.0 g Eu.sub.2O.sub.3

(40) Batch mixture 2:

(41) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.4 g Pr.sub.6O.sub.11, and 7.0 g Eu.sub.2O.sub.3

(42) Batch mixture 3:

(43) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.4 g Nd.sub.2O.sub.3, and 7.0 g Eu.sub.2O.sub.3

(44) Batch mixture 4:

(45) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.4 g Sm.sub.2O.sub.3, and 7.0 g Eu.sub.2O.sub.3

(46) Batch mixture 5:

(47) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.4 g Gd.sub.2O.sub.3, and 7.0 g Eu.sub.2O.sub.3

(48) Batch mixture 6:

(49) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.5 g Tb.sub.4O.sub.7, and 7.0 g Eu.sub.2O.sub.3

(50) Batch mixture 7:

(51) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.5 g Dy.sub.2O.sub.3, and 7.0 g Eu.sub.2O.sub.3

(52) Batch mixture 8:

(53) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.5 g Ho.sub.2O.sub.3, and 7.0 g Eu.sub.2O.sub.3

(54) Batch mixture 9:

(55) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.5 g Er.sub.2O.sub.3, and 7.0 g Eu.sub.2O.sub.3

(56) Batch mixture 10:

(57) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.5 g Tm.sub.2O.sub.3, and 7.0 g Eu.sub.2O.sub.3

(58) Batch mixture 11:

(59) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.5 g Yb.sub.2O.sub.3, and 7.0 g Eu.sub.2O.sub.3

(60) Batch mixture 12:

(61) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.5 g Lu.sub.2O.sub.3, and 7.0 g Eu.sub.2O.sub.3

(62) Batch mixture 13:

(63) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.4 g Y.sub.2O.sub.3, and 7.0 g Eu.sub.2O.sub.3

(64) Batch mixture 14:

(65) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.2 g Sc.sub.2O.sub.3, and 7.0 g Eu.sub.2O.sub.3

(66) Batch mixture 15:

(67) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.4 g In.sub.2O.sub.3, and 7.0 g Eu.sub.2O.sub.3

(68) A comparison of the spectral properties is shown in following Table 1 based on the example of a La/N doping with and without SiO.sub.2 deficiency.

(69) TABLE-US-00001 TABLE 1 λ.sub.exc. λ.sub.dom FWHM QE Composition [nm] x y [nm] [nm] [%] (Ba.sub.0.9575Sr.sub.0.9575La.sub.0.005Eu.sub.0.08) SiO.sub.3.995N.sub.0.005 460 0.285 0.638 545.9 64.2 87 (Ba.sub.0.9575Sr.sub.0.9575La.sub.0.005Eu.sub.0.08) v 460 0.285 0.639 545.9 64.1 100

(70) The spectral data of further embodiments are listed in following Table 2.

(71) TABLE-US-00002 TABLE 2 λ.sub.exc. λ.sub.dom FWHM QE Composition [nm] x y [nm] [nm] [%] (Ba.sub.0.9575Sr.sub.0.9575La.sub.0.005Eu.sub.0.08) Si.sub.0.9925O.sub.3.9875N.sub.0.005 60 285 639 5.9 4.1 1.00 (Ba.sub.0.9575Sr.sub.0.9575Pr.sub.0.005Eu.sub.0.08) Si.sub.0.9925O.sub.3.9875N.sub.0.005 60 288 636 6.4 4.4 0.95 (Ba.sub.0.9575Sr.sub.0.9575Sm.sub.0.005Eu.sub.0.08) Si.sub.0.9925O.sub.3.9875N.sub.0.005 60 285 638 5.9 5.0 0.89 (Ba.sub.0.9575Sr.sub.0.9575Gd.sub.0.005Eu.sub.0.08) Si.sub.0.9925O.sub.3.9875N.sub.0.005 60 286 637 6.1 5.4 0.97 (Ba.sub.0.9575Sr.sub.0.9575Tb.sub.0.005Eu.sub.0.08) Si.sub.0.9925O.sub.3.9875N.sub.0.005 60 290 637 6.9 5.2 1.02 (Ba.sub.0.9575Sr.sub.0.9575Dy.sub.0.005Eu.sub.0.08) Si.sub.0.9925O.sub.3.9875N.sub.0.005 60 289 637 6.7 5.1 1.00 (Ba.sub.0.9575Sr.sub.0.9575Ho.sub.0.005Eu.sub.0.08) Si.sub.0.9925O.sub.3.9875N.sub.0.005 60 292 635 7.2 5.7 0.98 (Ba.sub.0.9575Sr.sub.0.9575Er.sub.0.005Eu.sub.0.08) Si.sub.0.9925O.sub.3.9875N.sub.0.005 60 297 632 8.1 6.5 0.97 (Ba.sub.0.9575Sr.sub.0.9575Tm.sub.0.005Eu.sub.0.08) Si.sub.0.9925O.sub.3.9875N.sub.0.005 60 297 634 8.2 6.4 1.00 (Ba.sub.0.9575Sr.sub.0.9575Yb.sub.0.005Eu.sub.0.08) Si.sub.0.9925O.sub.3.9875N.sub.0.005 60 298 633 8.3 7.1 0.98 (Ba.sub.0.9575Sr.sub.0.9575Lu.sub.0.005Eu.sub.0.08) Si.sub.0.9925O.sub.3.9875N.sub.0.005 60 298 632 8.3 7.2 1.01 (Ba.sub.0.9575Sr.sub.0.9575Y.sub.0.005Eu.sub.0.08) Si.sub.0.9925O.sub.3.9875N.sub.0.005 60 294 635 7.6 5.5 1.02 (Ba.sub.0.9575Sr.sub.0.9575In.sub.0.005Eu.sub.0.08) Si.sub.0.9925O.sub.3.9875N.sub.0.005 60 301 630 8.8 8.0 0.99 (Ba.sub.0.9575Sr.sub.0.9575Sc.sub.0.005Eu.sub.0.08) Si.sub.0.9925O.sub.3.9875N.sub.0.005 60 296 633 8.0 6.9 1.00

(72) An embodiment of a white LED (according to the construction from FIG. 2) with the associated color space in comparison to the NTSC color space is shown in FIG. 4. The blue component is provided here by the primary radiation having the peak emission wavelength 448 nm of the LED, the green component is the secondary radiation, based on a modified nitrido-orthosilicate of the form (Ba.sub.0.9575Sr.sub.0.9575Lu.sub.0.005Eu.sub.0.08) Si.sub.0.9925O.sub.3.98N.sub.0.005, the red component is the secondary radiation, based on a red nitrido-aluminosilicate of the form CaAlSiN.sub.3:Eu.sup.2+. The associated spectrum is shown in FIG. 3.

(73) To be able to span a sufficiently large NTSC color space ≧85%, it is necessary to adapt the colorimetric locus of the luminescent substances by way of a suitable AE-RE ratio. This good adaptability is a particular advantage of the stabilized NOS. The dependence of the colorimetric locus on the relative Ba/Sr content in the stabilized nitrido-orthosilicate is described hereafter according to FIG. 3 as an example, wherein the color coordinates u′ and v′ are plotted as the abscissa and ordinate. This is accompanied by the influencing of the size of the NTSC color space, see FIG. 5. The largest color space is achieved here with a relative ratio Sr/Ba of 1:1 (curve (2)), and a ratio 1.1:0.9 according to curve (3) still displays acceptable results.

(74) The novel green nitrido-orthosilicate luminescent substance generally displays a higher chemical stability than conventional green orthosilicates, wherein the extent of the stabilization and the efficiency of the luminescent substance in the case of low and high currents are dependent on the “doping” with REN. Doping here means addition in small quantities.

(75) Embodiments of the nitrido-orthosilicate of the form (Ba.sub.0.9575Sr.sub.0.9575RE.sub.0.005Eu.sub.0.08)Si.sub.0.9925O.sub.3.98N.sub.0.005 for high-current efficiency or low-current efficiency are shown in FIG. 6. High-current operation typically means 500 mA, more generally at least 200 mA up to 700 mA. Low-current operation typically means 50 mA, more generally 30 mA up to 150 mA. Lu and Yb show the best results as RE doping here. The comparative example orthosilicate means BaSrSiO.sub.4:Eu as an orthosilicate without REN doping, the other luminescent substance is a luminescent substance stabilized with REN of the same type, wherein RE respectively denotes the specified element. An addition of Lu and Yb are at least equal to the pure orthosilicate in high-current suitability, with the additional advantage of colorimetric locus adaptation.

(76) The preparation of the described nitrido-orthosilicates of the form AE.sub.2-x-aRE.sub.xEu.sub.aSiO.sub.4N.sub.x, see also U.S. Pat. No. 7,489,073, or AE-.sub.2-x-aRE.sub.xEu.sub.aSi.sub.1-yO.sub.4-x-2yN.sub.x, is typically performed from AECO.sub.3, SiO.sub.2, REN, and Eu.sub.2O.sub.3 or AECO.sub.3, SiO.sub.2, Si.sub.3N.sub.4, (RE).sub.2O.sub.3, and Eu.sub.2O.sub.3 as starting substances. In the latter, the rare earths are used as (RE).sub.2O.sub.3, if trivalent oxides are preferably formed. In the case of rare earth oxides which are preferably provided as mixed oxides, for example, Tb is typically provided as a III/IV mixed oxide Tb.sub.4O.sub.7, the mixed oxides are preferably used.

(77) Furthermore, in particular fluorides and chlorides, such as AECl.sub.2 or RECl.sub.2, AEF.sub.2 or RECl.sub.2, but also NH.sub.4Cl/NH.sub.4F, H.sub.3BO.sub.3, LiF, and cryolites, and also combinations thereof, can be used as fluxes.

(78) The educts analogous to the batch mixtures 1 to 12 are weighed and homogenized, together with a suitable flux. Subsequently, the educt mixture is annealed for several hours under reducing atmosphere (e.g. under N.sub.2 or Ar or a mixture of N.sub.2/H.sub.2 or Ar/H.sub.2) at temperatures between 1000° C. and 1500° C. A secondary annealing can then be performed, also under reducing atmosphere (e.g. under N.sub.2 or Ar or a mixture of N.sub.2/H.sub.2 or Ar/H.sub.2) at temperatures between 800° C. and 1400° C. The synthesis is carried out in a suitable furnace, e.g., tube furnaces or chamber furnaces.

(79) Batch mixture 1:

(80) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.5 g La.sub.2O.sub.3, and 7.0 g Eu.sub.2O.sub.3

(81) Batch mixture 2:

(82) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.4 g Pr.sub.6O.sub.11, and 7.0 g Eu.sub.2O.sub.3

(83) Batch mixture 3:

(84) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.4 g Nd.sub.2O.sub.3, and 7.0 g Eu.sub.2O.sub.3

(85) Batch mixture 4:

(86) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.4 g Sm.sub.2O.sub.3, and 7.0 g Eu.sub.2O.sub.3

(87) Batch mixture 5:

(88) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.4 g Gd.sub.2O.sub.3, and 7.0 g Eu.sub.2O.sub.3

(89) Batch mixture 6:

(90) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.5 g Tb.sub.4O.sub.7, and 7.0 g Eu.sub.2O.sub.3

(91) Batch mixture 7:

(92) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.5 g Dy.sub.2O.sub.3, and 7.0 g Eu.sub.2O.sub.3

(93) Batch mixture 8:

(94) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.5 g Ho.sub.2O.sub.3, and 7.0 g Eu.sub.2O.sub.3

(95) Batch mixture 9:

(96) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.5 g Er.sub.2O.sub.3, and 7.0 g Eu.sub.2O.sub.3

(97) Batch mixture 10:

(98) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.5 g Tm.sub.2O.sub.3, and 7.0 g Eu.sub.2O.sub.3

(99) Batch mixture 11:

(100) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.5 g Yb.sub.2O.sub.3, and 7.0 g Eu.sub.2O.sub.3

(101) Batch mixture 12:

(102) 69.9 g SrCO.sub.3, 93.3 g BaCO.sub.3, 29.3 g SiO.sub.2, 0.1 g Si.sub.3N.sub.4, 0.5 g Lu.sub.2O.sub.3, and 7.0 g Eu.sub.2O.sub.3

(103) In this case, three variants of the nitrido-orthosilicate luminescent substance of the form AE.sub.2-x-aRE.sub.xEu.sub.aSi.sub.1-yO.sub.4-x-2yN.sub.x are preferred because of the behavior thereof upon the combined observation of aging stability and efficiency. Both aspects are equally significant for an illumination unit for LCD backlighting.

(104) 1. A nitrido-orthosilicate of the embodiment AE.sub.2-x-aLu.sub.xEu.sub.aSi.sub.1-yO.sub.4-x-2yN.sub.x, which has a higher chemical stability in comparison to commercial orthosilicates, see FIG. 7 in this regard, and displays comparable efficiency both in the case of low currents and also in the case of high LED currents, see FIG. 6 in this regard. Normal orthosilicate without REN but of otherwise identical composition is selected as a benchmark. The described NOS: Lu is (Ba.sub.0.9575Sr.sub.0.9575Lu.sub.0.005Eu.sub.0.08) Si.sub.0.9925O.sub.3.98N.sub.0.005 under blue primary excitation at 447 nm.
2. A nitrido-orthosilicate of the embodiment AE.sub.2-x-aYb.sub.xEu.sub.aSi.sub.1-yO.sub.4-x-2yN.sub.x, which has a higher chemical stability in the LED in comparison to commercial orthosilicates, see FIG. 8 in this regard, and displays comparable efficiency both in the case of low currents and also in the case of high LED currents, see FIG. 6 in this regard. The described NOS:Yb is (Ba.sub.0.9575Sr.sub.0.9575Yb.sub.0.005Eu.sub.0.08) Si.sub.0.9925O.sub.3.98N.sub.0.005 under blue primary excitation at 448 nm.
3. A nitrido-orthosilicate of the embodiment AE-.sub.2-x-aDy.sub.xEu.sub.aSi.sub.1-yO.sub.4-x-2yN.sub.x, which has a higher chemical stability in the LED in comparison to commercial orthosilicates, see FIG. 9 in this regard, and displays comparable efficiency in the case of low currents and nearly comparable efficiency in the case of high LED currents, see FIG. 6 in this regard. The described NOS: Dy is (Ba.sub.0.9575Sr.sub.0.9575Dy.sub.0.005Eu.sub.0.08) Si.sub.0.9925O.sub.3.98N.sub.0.005 under blue primary excitation at 447 nm.

(105) The properties of the above-described luminescent substance combinations permit the implementation of coverage of at least 85% of the NTSC color space with very good aging stability and efficiency.

(106) For applications which place high chemical stability claims, a nitrido-orthosilicate of the embodiment AE.sub.2-x-aLa.sub.xEu.sub.aSi.sub.1-yO.sub.4-x-2yN.sub.x, which has an extremely high chemical stability in the LED in comparison to commercial orthosilicates, can be used, see FIG. 10 and FIG. 11 for various proportions of La, with comparable efficiency in the case of low operating currents, see FIG. 6. The described NOS:La shown in FIG. 10 is (Ba.sub.0.9575Sr.sub.0.9575La.sub.0.005Eu.sub.0.08) Si.sub.0.9925O.sub.3.98N.sub.0.005 under blue primary excitation at 447 nm. The La proportion is 0.0025 in FIG. 11.

(107) Finally, FIG. 12 shows a comparison of the various currently used color spaces. NTSC is one of the largest defined color spaces overall. It is correspondingly difficult to represent using technical solutions. The greater the overlap with this color space by a technical solution, the more colors can thus be displayed on a television, for example.

(108) The term 85% NTSC means that using a corresponding light source, specifically a combination of LED (blue) and two luminescent substances (red and green), after filtering by the red and green color filters, 85% of the area of this color space can be covered. For such a large color space, unusually narrowband luminescent substances are necessary, which preferably only have an FWHM of 70 nm or less. Therefore, for the implementation of the NTSC color space, most luminescent substances cannot be used, in particular, for example, no garnets or modified garnets. One example is the possible use of LuAGaG:Ce, which, as a result of its non-narrowband nature, can only be used for the very much smaller color space sRGB (shown in FIG. 12), but certainly not for the NTSC color space.

(109) Surprisingly, the reliable implementation has heretofore only been successful using selected modified nitrido-orthosilicates, if RE is selected to be Lu, Dy, La, or Yb or a combination thereof.

(110) FIG. 13 shows a luminescent substance lamp 90 having a bulb 91 and two electrodes 92. It contains a typical filler, which has mercury, and a luminescent substance layer 93 incorporating an NOS luminescent substance having batch stoichiometry of the formula EA.sub.2-x-aRE.sub.xEu.sub.aSi.sub.1-yO.sub.4-x-2yN.sub.x.

(111) FIGS. 14A and 14B show the influence of SiO.sub.2 as a filler material in the casting material on the stabilization of the colorimetric locus as a function of the temperature. At a proportion of 10 wt.-% SiO.sub.2, the exemplary embodiment shown is successful in keeping the colorimetric locus shift, which relates to the x coordinate, at less than 0.001 in a temperature range from 25° C. to 145° C. The y coordinate may not be stabilized as well, however, SiO.sub.2 also has a positive influence here. Above all, a proportion of SiO.sub.2 in the range from 5 to 15% is recommended. Further components of the casting material are substantially silicone and luminescent substance.

(112) While the disclosed embodiments have been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the disclosed embodiments as defined by the appended claims. The scope of the disclosed embodiments is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.