Phosphors which can be efficiently excited with ultraviolet, blue or green primary radiation and have an efficient emission in the blue, green, yellow, red or deep-red spectral range are of very great interest for the production of white and colored light-emitting diodes (LEDs). Such so-called conversion LEDs are used for many applications, for example for general lighting, display backlighting, signage, in automobiles and in numerous further consumer products. In order to obtain an increase in efficiency, a higher robustness, a better color quality, color space coverage and/or color fidelity of the conversion LEDs, in order firstly to improve the applications and secondly to extend the application spectrum of the conversion LEDs, there is great demand for new phosphors.
Known phosphors having an emission in the green to red spectral range with a relatively small full width at half maximum (FWHM) are, for example, EAS:Eu or EAGa2S4:Eu (EA=alkaline earth metals). However, these phosphors are not very robust and exhibit a temperature-dependent decrease in the intensity of the emitted radiation (thermal quenching).
Nitridosilicates and nitridoalumosilicates of the formula M2Si5N8:Eu, MAlSiN3:Eu or MM′Si2Al2N6:Eu where M, M′=Mg, Ca, Sr or M,M′=Mg,Ca,Sr,Ba emit in the orange to red spectral range and are very efficient and stable. What is disadvantageous about these phosphors is the relatively large full width at half maximum of the emission band, their expensive starting materials and a complex production method. In some instances, these phosphors are also not resistant to moisture.
Garnets of the formula A3B5O12:Ce (A=rare earth metal, B=Al,Ga) and their derivatives emit in the green and yellow spectral range and have a high resistance and a high conversion efficiency. What is disadvantageous about these phosphors is the relatively large full width at half maximum of the emission band and limited adjustability of the emission wavelength. In this regard, an emission in the red spectral range cannot be achieved, for example.
Orthosilicates and oxonitridoorthosilicates of the formula M2SiO4:Eu, M2−x−aRExEuaSiO4−xNx or M2−x−aRExEuaSi1−yO4−x−2yNx (M=Sr, Ba, Ca, Mg; RE=rare earth metal) emit radiation in the green to orange spectral range. The main disadvantages of these phosphors are a relatively large full width at half maximum of the emission band and a limited adjustability of the emission wavelength; an emission in the red spectral range cannot be achieved, for example. Moreover, the phosphors exhibit a thermal quenching behavior and are not very robust.
Oxonitridosilicates and SiAlONs of the formula MSi2O2N2:Eu, Si6−zAlzOzN8−z:RE or Si6−xAlzOyN8−y:REz (RE=rare earth metal) emit radiation in the blue to yellow spectral range. The main disadvantages of these phosphors are a relatively large full width at half maximum of the emission band and a limited adjustability of the emission wavelength. Moreover, the phosphors in some instances are not very efficient and stable and are expensive to produce inter alia owing to expensive starting materials.
Nitridoaluminates of the formula MLiAl3N4:Eu (M=Ca,Sr) emit in the deep-red spectral range and have a high radiation stability and a high conversion efficiency. A limited adjustability of the emission wavelength is disadvantageous; a narrowband emission in the green and yellow spectral range cannot be achieved, for example. Moreover, these phosphors are expensive to produce and moreover in some instances are not resistant to moisture influences.