Synthesis, structure and properties of a calcium oxonitridosilicate phosphor showing green or red luminescence upon doping with Eu2+ or Ce3.

The phase LixCa16-xSi17N32-xO2+x was synthesized by solid-state metathesis at 1050 °C in weld-sealed niobium ampoules. The crystal structure was solved from powder X-ray diffraction data in the space group F4[combining macron]3m (a = 14.7391(1) Å, Z = 4); it is closely related to the previously reported structure of Ca16Si17N34. The structure of LixCa16-xSi17N32-xO2+x is based on a complex network of [SiN4] tetrahedra with interstitial voids filled by Ca ions, partially substituted by Li. This Li substitution is charge-compensated by replacement of N by O in the structure. Theoretical calculations confirm that the unit cell volume decreases with increasing stoichiometric factor x. Europium doped samples of this compound show intense Eu2+ emission at 536 nm on excitation with near-UV or blue radiation at 350-480 nm. Ce3+ doping yields orange to red emission with two broad emission bands at 600 and 665 nm.