YELLOW LUMINOPHORE AND LIGHT SOURCE

Abstract

A luminophore having the general empirical formula X′.sub.1−xA′.sub.y(Al.sub.1+zA′.sub.3−z) O.sub.4:E′ that crystallizes in a tetragonal crystal system. X′ may be Mg, Ca, Sr, Ba, and combinations thereof; A′ may be Li, Na, K, Rb, Cs, and combinations thereof; E′ may be Eu, Ce, Yb, Mn, and combinations thereof; 0<x<0.25; y≤x; and z=0.5(2x−y).

Claims

1-7. (canceled)

8. A luminophore having the general empirical formula X′.sub.1−xA′.sub.y(Al.sub.1+zA′.sub.3−z) O.sub.4:E′ that crystallizes in a tetragonal crystal system; wherein: X′ is selected from the group consisting of Mg, Ca, Sr, Ba, and combinations thereof; A′ is selected from the group consisting of Li, Na, K, Rb, Cs, and combinations thereof; E′ is selected from the group consisting of Eu, Ce, Yb, Mn, and combinations thereof; 0<x<0.25; y≤x; and z=0.5 (2x−y).

9. The luminophore as claimed in claim 8, wherein the luminophore has the general empirical formula X′.sub.1−xLi.sub.y(Al.sub.1+zLi.sub.3−z) O.sub.4:E′.

10. The luminophore as claimed in claim 8, wherein the luminophore has the general empirical formula Sr.sub.1−xLi.sub.y(Al.sub.1+zLi.sub.3−z) O.sub.4:E′.

11. The luminophore as claimed in claim 8, wherein x=y.

12. The luminophore as claimed in claim 8, wherein 0.10<x<0.18.

13. The luminophore as claimed in claim 8, wherein the luminophore crystallizes in the tetragonal space group I4/m.

14. A luminophore mixture comprising: a luminophore having the general empirical formula XA.sub.3AlO.sub.4:E that crystallizes in a triclinic crystal system, wherein: X is selected from the group consisting of Mg, Ca, Sr, Ba, and combinations thereof; A is selected from the group consisting of Li, Na, K, Rb, Cs, and combinations thereof and E is selected from the group consisting of Eu, Ce, Yb, Mn and combinations thereof; and a luminophore having the general empirical formula X′.sub.1−xA′.sub.y(Al.sub.1+zA′.sub.3−z) O.sub.4:E′ that crystallizes in a tetragonal crystal system, wherein: X′ is selected from the group consisting of Mg, Ca, Sr, Ba, and combinations thereof; A′ is selected from the group consisting of Li, Na, K, Rb, Cs, and combinations thereof; E′ is selected from the group consisting of Eu, Ce, Yb, Mn, and combinations thereof; 0<x<0.25; y≤x; and z=0.5 (2x−y).

15. A light source comprising a luminophore as claimed in claim 8.

16. The light source as claimed in claim 15, further comprising: at least one primary radiation source configured to emit electromagnetic primary radiation; and a conversion element comprising the luminophore; and wherein the conversion element is configured to at least partially convert the electromagnetic primary radiation to electromagnetic secondary radiation.

17. The light source as claimed in claim 16, wherein the light source is configured to emit a white overall radiation or to emit a yellow overall radiation.

18. The light source as claimed in claim 15, wherein the at least one primary radiation source is a light-emitting diode or a laser diode.

19. The light source as claimed in claim 18, wherein the primary radiation source is a laser diode.

20. The light source as claimed in claim 19, wherein the conversion element is a rotatable luminophore wheel.

21. A floodlight comprising a light source as claimed in claim 19.

22. The floodlight as claimed in claim 21, wherein the floodlight is a motor vehicle headlight.

23. The floodlight as claimed in claim 21; wherein the floodlight is arranged in general lighting, exterior lighting, security lighting, stage lighting, or specialty lighting.

24. The light source as claimed in claim 15; wherein the light source is arranged in a display or projector.

25. A light source comprising a luminophore as claimed in claim 14.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0107] Further advantageous embodiments and developments are apparent from the working examples described hereinafter in conjunction with the figures.

[0108] FIG. 1 shows a detail of the crystal structure of the luminophore.

[0109] FIGS. 2, 3, 4, 5, 6, 7, 8 show emission spectra.

DETAILED DESCRIPTION

[0110] FIG. 1 shows a detail of the crystal structure (monoclinic, P1 space group) of the inventive luminophore of the formula SrLi.sub.3AlO.sub.4:Eu.sup.2+. The crystal structure was determined by means of single-crystal x-ray diffraction. The lattice parameters, crystallographic data and the quality parameters of the x-ray determination can be found in table 3, and the crystallographic position parameters of the refined structures in tables 4a and 4b. The crystal structure of the luminophore corresponds to that of Sr[LiAl.sub.3N.sub.4]:Eu.sup.2+ (Pust, P. et al. Narrow-band red-emitting Sr[LiAl.sub.3N.sub.4]:Eu.sup.2+ as a next-generation LED-phosphor material. Nat. Mater. (2014)). In FIG. 1, filled circles represent Sr, hatched tetrahedra represent LiO.sub.4 tetrahedra, and filled tetrahedra represent AlO.sub.4 tetrahedra. In the tetrahedra, there are oxygen atoms at each of the vertices, and Al or Li in the center of the tetrahedra.

[0111] FIG. 2 shows the emission spectrum of the luminophore SrLi.sub.3AlO.sub.4:Eu.sup.2+ (AB1). Plotted on the x axis is the wavelength in nanometers, and on the y axis the relative intensity in percent. On excitation with blue primary radiation, the luminophore emits yellow secondary radiation with a dominant wavelength λ.sub.dom=568 nm and a peak wavelength λ.sub.peak=566 nm. As well as the peak wavelength, the emission band EB has an emission maximum EM. The spectral half-height width of the emission band is 46 nm.

[0112] FIG. 3, like FIG. 2, shows the emission spectrum of the luminophore SrLi.sub.3AlO.sub.4:Eu.sup.2+ (AB1). It becomes clear here that the emission band EB results from a partial overlap of two emission peaks EP1 and EP2. EP1 has a lower intensity than EP2. The resulting emission band EB has an emission maximum EM resulting from EP1 and a further emission maximum corresponding roughly to the peak wavelength resulting from EP2. The emission maximum of EP1 is about 520 nm, the emission maximum of EP2 about 570 nm. The spectral half-height width of EP1 is about 40 nm, that of EP2 about 46 nm.

[0113] FIG. 4 shows the emission spectrum of the luminophore SrLi.sub.3AlO.sub.4:Eu.sup.2+ (AB2). On excitation with blue primary radiation, the luminophore emits yellow secondary radiation having a dominant wavelength λ.sub.dom=555 nm and a peak wavelength λ.sub.peak=521 nm. As well as the peak wavelength, the emission band has an emission maximum EM. The spectral half-height width of the emission band is 85 nm.

[0114] FIG. 5, like FIG. 4, shows the emission spectrum of the luminophore SrLi.sub.3AlO.sub.4:Eu.sup.2+ (AB2). It becomes clear here that the emission band EB results from a partial overlap of two emission peaks EP1 and EP2. EP2 has lower intensity than EP1. The resulting emission band EB has an emission maximum EM resulting from EP2 and a further emission maximum corresponding roughly to the peak wavelength λ.sub.peak resulting from EP1. As is clearly apparent in the emission spectrum, the emission maximum EM of the emission band is shifted to a slightly shorter wavelength compared to the emission maximum of the emission peak EP2, while the peak wavelength λ.sub.peak of the emission band is shifted to a slightly longer wavelength compared to the emission maximum of the emission peak EP1. The emission maximum of EP1 is about 520 nm, the emission maximum of EP2 about 570 nm. The spectral half height width of EP1 is about 40 nm, that of EP2 about 46 nm.

[0115] A comparison with the emission spectrum of AB1 from FIG. 3 shows that, for AB1, the intensity of EP1 is lower than that of EP2, whereas, for AB2, the intensity of EP2 is lower than that of EP1. The emission spectra of AB1 and AB2 of FIGS. 2 to 5 thus show that the ratio of the emission peaks EP1 and EP2 to one another is variable, and at least the emission peak EP1 can be suppressed completely or virtually completely (see FIGS. 2 and 3). The emission band of AB1 therefore nearly corresponds to the emission peak EP2.

[0116] The inventors have thus surprisingly succeeded in providing a luminophore having a peak length within a range between 510 nm and 530 nm inclusive or between 560 and 580 nm inclusive. The position of the peak wavelength depends on the relative intensity of the two emission peaks of the emission band, it being possible by variation of the synthesis conditions for the emission peak EP1 in particular to have a very low intensity or be suppressed completely.

[0117] FIG. 6 shows a comparison of the emission spectrum of AB1 with that of the luminophore Y.sub.3Al.sub.5O.sub.12:Ce.sup.3+ (VB1). VB1, measured by the dominant wavelength λ.sub.dom, has a comparable color impression to the inventive luminophore AB1.

[0118] FIG. 7 shows a comparison of the emission spectrum of AB2 with that of the luminophore Lu.sub.3Al.sub.5O.sub.12:Ce.sup.3+ (VB2). VB2, measured by the dominant wavelength λ.sub.dom, has a comparable color impression to the inventive luminophore AB2.

[0119] As is clearly apparent from FIGS. 6 and 7, the working examples AB1 and AB2 have much lower spectral half-height widths than the corresponding comparative examples VB1 and VB2. In both cases, this lower spectral half-height width leads to a distinct increase in luminous efficacy of radiation (LER), as can be seen from the relative light yield

[00001]$\frac{{\eta }_v\left(\mathrm{working}\mathrm{example}\right)}{{\eta }_v\left(\mathrm{comparative}\mathrm{example}\right)}$

shown in table 7.

TABLE-US-00008 TABLE 7 Luminophore λ.sub.dom FWHM [00002]$\mathrm{LER}=\frac{{\eta }_v\left(\mathrm{working}\mathrm{example}\right)}{{\eta }_v\left(\mathrm{comparative}\mathrm{example}\right)}$ VB1: Y.sub.3Al.sub.5O.sub.12 567 nm 46 nm 100% AB1: SrLi.sub.3AlO.sub.4:Eu.sup.2+ 568 nm 116 nm 122% VB2: Lu.sub.3Al.sub.5O.sub.12 555 nm 85 nm 100% AB2: SrLi.sub.3AlO.sub.4:Eu.sup.2+ 555 nm 110 nm 120%

[0120] This increase by about 20% in the light yield of the working examples of the luminophore is directly advantageous for most conversion-based light sources. Used as a single luminophore in a full conversion solution, this elevated light yield corresponds to the gain in efficiency of the conversion solution when the luminophores are used.

[0121] These distinct advantages extend not just to full conversion applications with just a single luminophore. As part of a conversion solution with multiple luminophores (e.g. white light-emitting light sources), the gain in efficiency by virtue of the luminophore can still lead to distinct improvements. However, exact size of the gain in efficiency in a mixture also depends on the other luminophores in the mixture.

[0122] FIG. 8 shows the emission spectrum of the luminophore Sr.sub.0.86Li.sub.0.14 (Li.sub.2.93Al.sub.1.07) O.sub.4:Eu.sup.2+ (AB1′). Plotted on the x axis is the wavelength in nanometers, and on the y axis the relative intensity in percent.

[0123] The working examples described in conjunction with the figures and the features thereof can also be combined with one another in further working examples, even if such combinations are not shown explicitly in the figures. In addition, the working examples described in conjunction with the figures may have additional or alternative features according to the description in the general part.

LIST OF REFERENCE NUMERALS

[0124] EP1 emission peak [0125] EP2 emission peak [0126] EB emission band [0127] EM emission maximum [0128] LED light-emitting diode [0129] LER light yield [0130] FWHM half-height width [0131] λ.sub.dom dominant wavelength [0132] λ.sub.peak peak wavelength [0133] AB working example [0134] VB comparative example [0135] g grams [0136] I intensity [0137] mol % mole percent [0138] nm nanometers [0139] ° C. degrees Celsius