RED EMITTING LUMINESCENT MATERIAL

Abstract

A red-emitting phosphor comprising an Eu.sup.2+ doped nitridoaluminate phosphor is provided. The red emitting phosphor comprises an emission maximum in the range of 610 to 640 nm of the electromagnetic spectrum.

Claims

1-14. (canceled)

15. A red-emitting phosphor comprising an Eu.sup.2+ doped nitridoaluminate phosphor, wherein the red-emitting phosphor comprises an emission maximum in the range of 610 to 640 nm of the electromagnetic spectrum, and wherein the red-emitting phosphor comprises a half-width of less than 65 nm.

16. Red-emitting phosphor according to claim 15, wherein the red-emitting phosphor comprises the elements Ca, Li, Al, N and Eu.

17. Red-emitting phosphor according to claim 15, wherein the red-emitting phosphor comprises an emission maximum in the range of 620 to 635 nm.

18. Red-emitting phosphor according to claim 15, wherein the red-emitting phosphor comprises the elements Ca, Li, Al, N and Eu.

19. Red-emitting phosphor according to claim 15, wherein the red-emitting phosphor consists of the elements Ca, Li, Al, N and Eu.

20. Red-emitting phosphor according to claim 19, wherein the red-emitting phosphor is prepared from starting materials comprising Li.sub.3N, LiAlH.sub.4, AlN, Ca.sub.3N.sub.2 and EuF.sub.3.

21. Red-emitting phosphor according to claim 20, wherein the molar ratio of the starting materials corresponds to the molar composition Ca.sub.1−xLiAl.sub.3N.sub.4Eu.sub.x, where x=0.001 to 0.01.

22. Red-emitting phosphor according to claim 15, wherein the red-emitting phosphor comprises a dominant wavelength of λ<620 nm.

23. A red-emitting phosphor comprising an Eu.sup.2+ doped nitridoaluminate phosphor, wherein the red-emitting phosphor comprises an emission maximum in the range of 610 to 640 nm of the electromagnetic spectrum, and wherein the red-emitting phosphor comprises a dominant wavelength of λ<620 nm.

24. Red-emitting phosphor according to claim 23, wherein the red-emitting phosphor has a half-width of less than 65 nm, and the red-emitting phosphor comprises the elements Ca, Li, Al, N and Eu.

25. Red-emitting phosphor according to claim 23, wherein the red-emitting phosphor comprises an emission maximum in the range of 620 to 635 nm.

26. Red-emitting phosphor according to claim 23, wherein the red-emitting phosphor comprises a half-width of less than 65 nm.

27. Red-emitting phosphor according to claim 23, wherein the red-emitting phosphor comprises the elements Ca, Li, Al, N and Eu.

28. Red-emitting phosphor according to claim 23, wherein the red-emitting phosphor consists of the elements Ca, Li, Al, N and Eu.

29. Red-emitting phosphor according to claim 23, wherein the red-emitting phosphor is prepared from starting materials comprising Li.sub.3N, LiAlH.sub.4, AlN, Ca.sub.3N.sub.2 and EuF.sub.3.

30. Red-emitting phosphor according to claim 29, wherein the molar ratio of the starting materials corresponds to the molar composition Ca.sub.1−xLiAl.sub.3N.sub.4Eu.sub.x, where x=0.001 to 0.01.

31. A red-emitting phosphor comprising an Eu.sup.2+ doped nitridoaluminate phosphor, wherein the red-emitting phosphor comprises an emission maximum in the range of 610 to 640 nm of the electromagnetic spectrum, and wherein the red-emitting phosphor is prepared from starting materials comprising Li.sub.3N, LiAlH.sub.4, AlN, Ca.sub.3N.sub.2 and EuF.sub.3.

32. Red-emitting phosphor according to claim 31, wherein the red-emitting phosphor has a half-width of less than 65 nm, and the red-emitting phosphor comprises the elements Ca, Li, Al, N and Eu.

33. Red-emitting phosphor according to claim 31, wherein the red-emitting phosphor comprises an emission maximum in the range of 620 to 635 nm.

34. Red-emitting phosphor according to claim 31, wherein the molar ratio of the starting materials corresponds to the molar composition Ca.sub.1−xLiAl.sub.3N.sub.4Eu.sub.x, where x=0.001 to 0.01.

Description

[0065] Further advantageous embodiments and developments of the invention will become apparent from the embodiments described below in conjunction with the figures.

[0066] FIG. 1 shows an emission spectrum of an exemplary embodiment of a red-emitting phosphor in comparison to emission spectra of two known phosphors,

[0067] FIG. 2 shows characteristic properties of a first and a second embodiment of a red-emitting phosphor in comparison to two known phosphors,

[0068] FIGS. 3 and 4 show X-ray powder diffraction patterns of an embodiment of a red emitting phosphor using copper-K.sub.α1-radiation.

[0069] FIG. 1 shows the emission spectrum of a first exemplary embodiment of the phosphor according to the invention (curve with the reference symbol Ia). In addition, an emission spectrum of the known phosphor CaLiAl.sub.3N.sub.4:Eu.sup.2+ (curve with the reference numeral Ma) and an emission spectrum of the known phosphor SrLiAl.sub.3N.sub.4:Eu.sup.2+ (curve with the reference numeral IIa) is shown. The wavelength is plotted in nanometers on the x-axis and the emission intensity in percent on the y-axis.

[0070] To measure the emission spectra, the phosphor according to the invention was excited with a blue LED having an emission radiation of 460 nm. The phosphor according to the invention has a half-width of 57 nm and a dominant wavelength of 611 nm, the maximum of the emission is 634 nm. Thus, the phosphor of the present invention emits almost only in the visible region of the electromagnetic spectrum, resulting in an increase in the overlap with the eye sensitivity curve and thus in the reduction of efficiency losses. The known phosphor CaLiAl.sub.3N.sub.4:Eu.sup.2+ was excited with an emission radiation of 470 nm and the known phosphor SrLiAl.sub.3N.sub.4:Eu.sup.2+ was excited with an emission radiation of 440 nm. As can be seen, the known phosphor SrLiAl.sub.3N.sub.4:Eu.sup.2+ has an emission maximum at about 650 nm and the known phosphor CaLiAl.sub.3N.sub.4:Eu.sup.2+ an emission maximum at about 670 nm.

[0071] The half-widths of the known phosphors are approximately in the same range as in the phosphor according to the invention. Due to the emission maximum of the phosphor according to the invention, which is shifted into the blue spectral range in comparison with the known phosphors, the inventive phosphor has a significantly increased luminescence efficiency. The phosphor according to the invention thus has an increased overlap with the eye sensitivity curve, which leads to the reduction of efficiency losses.

[0072] The first embodiment of the phosphor according to the invention, which has the emission spectrum with the reference Ia in FIG. 1, was prepared as follows: 0.064 mol Ca.sub.3N.sub.2, 0.032 Li.sub.3N, 0.096 mol LiAlH.sub.4, 0.432 mol AlN and 0.00019 mol EuF.sub.3 are homogeneously mixed. The molar ratio AlN:Ca.sub.3N.sub.2:Li.sub.3N:LiAlH.sub.4:EuF.sub.3 is 1:0.148:0.074:0.22:0.00044. This corresponds to a europium content of 0.1 mol % with respect to the amount of Ca in the starting materials. The mixture is transferred to a tungsten crucible, which is transferred to a tube furnace. Under a forming gas atmosphere (N.sub.2:H.sub.2=92.5:7.5), the mixture is heated at a heating rate of 250° C. per hour to a temperature of 1250° C. The mixture is annealed for one hour at a temperature of 1250° C., followed by cooling to room temperature with a cooling rate of 250° C. per hour.

[0073] FIG. 2 shows characteristic data of the first embodiment (A1) and a second embodiment (A2) in comparison to the known phosphors SrLiAl.sub.3N.sub.4:Eu.sup.2+ and CaLiAl.sub.3N.sub.4:Eu.sup.2+. λ.sub.dom is the dominant wavelength in nanometers, λ.sub.max is the maximum emission in nanometers, x, y are the coordinates of the emitted radiation within the CIE standard table (1931), LE is the luminescence efficiency in % and FWHM is the half-width in nanometers. The luminescence efficiency is given in percent and refers to the maximum of the luminescence efficiency at 555 nm. At 555 nm, the luminescence is 683 lumens/watt. The data provided with * are taken from the literature or are calculated from the literature data. All other data are experimental data of the inventors. The synthesis of the first embodiment Al is described under with FIG. 1.

[0074] The second embodiment of the phosphor according to the invention was prepared as follows: 9.430 g Ca.sub.3N.sub.2, 1.112 g Li.sub.3N, 3.630 g LiAlH.sub.4, 17.670 g AlN and 0.158 g EuF.sub.3 are homogeneously mixed. The mixture is transferred to a tungsten crucible, which is transferred to a tube furnace. Under a forming gas atmosphere (N.sub.2:H.sub.2=92.5:7.5), the mixture is heated at a heating rate of 250° C. per hour to a temperature of 1125° C. The mixture is annealed for 24 hours at a temperature of 1125° C., followed by a cooling to room temperature with a cooling rate of 45° C. per hour.

[0075] FIG. 3 shows two X-ray powder diffraction patterns using copper-K.sub.α1-radiation. The diffraction angles are given in ° 2θ-values on the x-axis and the intensity on the y-axis. The X-ray powder diffraction pattern provided with the reference I shows the diffraction pattern of the first embodiment of the red-emitting phosphor according to the invention, which was synthesized as provided under FIG. 1. The X-ray diffraction data were recorded by means of a surface sample carrier on a powder diffractometer (PANalytical Empyrean) with X-Celerator CCD detector in Bragg-Brentano geometry. The X-ray diffraction powder pattern provided with reference II is a simulated diffraction pattern of the compound of formula SrLiAl.sub.3N.sub.4 based on Nature Materials 2014, P. Pust et al., “Narrow-band red-emitting Sr[LiAl.sub.3N.sub.4]:Eu.sup.2+ as a next-generation LED-phosphor material”. From the illustrated X-ray powder diffraction patterns it is clear that the red-emitting phosphor according to the invention has a different crystal structure than the known phosphor of the formula SrLiAl.sub.3N.sub.4:Eu.sup.2+.

[0076] FIG. 4 shows two X-ray powder diffraction patterns using copper-K.sub.α1-radiation. The diffraction angles are given in ° 2θ-values on the x-axis and the intensity on the y-axis. The X-ray powder diffraction pattern provided with the reference I shows that of the first embodiment of the red emitting phosphor according to the invention, which was synthesized as provided under FIG. 1. The X-ray diffraction data were recorded by means of a surface sample carrier on a powder diffractometer (PANalytical Empyrean) with X-Celerator CCD detector in Bragg-Brentano geometry. The X-ray powder diffraction pattern provided with the reference III is a simulated compound of the formula CaLiAl.sub.3N.sub.4 based on Chemistry of Materials 2014, 26, P. Pust et al., “Ca[LiAl.sub.3N.sub.4]:Eu.sup.2+—a narrow-band red-emitting nitridolithoaluminate”. From the illustrated X-ray powder diffraction patterns it is clear that the red emitting phosphor of the invention has a different crystal structure than the known phosphor of the formula CaLiAl.sub.3N.sub.4:Eu.sup.2+.

[0077] The invention is not limited by the description based on the embodiments therein. Rather, the invention encompasses any novel feature as well as any combination of features, which includes in particular any combination of features in the patent claims, even if this feature or combination itself is not explicitly stated in the patent claims or exemplary embodiments.

[0078] This patent application claims the priority of German Patent Application 10 2015 119 149.0, the disclosure of which is hereby incorporated by reference.

REFERENCE NUMBERS

[0079] E emission intensity [0080] Ia, IIIa, Iia emission spectra [0081] nm nanometer [0082] λ wavelength [0083] A1 first embodiment [0084] A2 second embodiment [0085] k.sub.dom dominant wavelength [0086] λ.sub.max maximum emission [0087] x,y coordinates in the CIE standard table (1931) [0088] LE luminescence efficiency [0089] FWHM half-width [0090] I, II, III X-ray powder diffraction patterns