Illuminant and light source containing the same, and method for producing said illuminant
View Patent ↗An illumination from the class of oxynitridosilicates, doped with bivalent europium and comprising a cation M2+, said illuminant corresponding to the basic formula M (l-c) Si 2 0 2 N 2 :D c wherein the following holds good: M=Sr (1-x) Ba x mit 0.3<x<0.7.
1. A process of making a high-efficiency phosphor from the class of oxynitridosilicates with a cation M 2+ and an empirical formula M (1-c) SiO 2 N 2 :D c , where M 2+ simultaneously contains as constituents Sr 2+ and Ba 2+ , and where D is a divalent dopant with at least europium, wherein Sr (1-x) Ba x , where 0.45≦x≦0.55, is used for M, the oxynitridosilicate completely or predominantly comprising a mixed sion phase which corresponds neither to that of pure Sr sion phase nor that of pure Ba sion phase, the dominant wavelength of the mixed sion phase with the given doping content being shifted by at least 6 nm, with respect to the dominant wavelength of the pure Sr sion phase with the same doping content towards longer wavelengths, wherein the europium makes up from 5 to 12 mol % of M, wherein the process comprises:
1) mixing carbonates of Sr and of Ba intensively together with SiO 2 and a flux as well as with an Eu precursor,
2) annealing the mixture obtained in step 1) to synthesize an orthosilicate,
3) mixing the orthosilicate with a substantially stoichiometric batch of Si 3 N 4 , and
4) annealing the mixture obtained in step 3) in a slightly reducing atmosphere.
2. The process according to claim 1 , wherein the annealing in step 2) is conducted in the presence of forming gas.
3. The process according to claim 1 , wherein the annealing in step 2) is conducted in an Al 2 O 3 crucible in the presence of forming gas.
4. The process according to claim 1 , wherein the annealing in step 2) is conducted stepwise for a period of several hours at a temperature of up to approximately 1100-1400° C.