New luminescent rare earth activated oxynitridosilicates and oxynitridogermanates with the apatite structure

New luminescent oxynitrides based on the apatite structure doped with Eu2+ and Ce3+ have been prepared by ammonolysis of oxysilicate or oxygermanate precursors. The host compounds have the general formula La10-xSrx(Si/Ge)(6)O27-x/2-3y/2Ny. When doped with divalent europium or trivalent cerium they present blue, green, yellowish green or orange luminescence under UV/blue excitation. Remarkable long wavelength emissions centred beyond 500 nm are observed for the Ce3+ activated oxynitridosilicates and oxynitridogermanates, with compositions La8.9Ce0.1SrSi6N0.37O25.95, La8.9Ce0.1SrSi6N1.06O24.91 (lambda(em) = 545 nm) and La9.9Ce0.1Ge6N2.46O23.31 (lambda(em) = 590 nm). The treatment of precursor oxides with the required cationic ratios in NH3 gas was used as a convenient general method to prepare the oxynitride materials at moderate temperatures. This allowed decreasing the nitriding temperature from 1600-1400 degrees C to 1050-600 degrees C with respect to the method generally used for the synthesis of luminescent (oxy)nitride silicates, the solid state reaction between oxides, nitrides and carbonates under a N-2 or N-2-H-2 flow.