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

摘要

New luminescent oxynitrides based on the apatite structure doped with Eu~(2+) and Ce~(3+) have been prepared by ammonolysis of oxysilicate or oxygermanate precursors. The host compounds have the general formula La_(10-x)Sr_x(Si/Ge)6O_(27-x/2-3y/2N_y. 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 Ce~(3+) activated oxynitridosilicates and oxynitridogermanates, with compositions La_(8.9)Ce_(0.1)SrSi6N_(0.37)O_(25.95), La_(8.9)Ce_(0.1)SrSi6N_(1.06)O_(24.91) (λ_(em) = 545 nm) and La_(9.9)Ce_(0.1)Ge6N_(2.46)O_(23.31) (λ_(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 °C to 1050-600 °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 N2 or N2-H2 flow.