Luminescence of Eu-doped langasite nanopowders synthesized by a modified Pechini route

Abstract

Europium doped langasite (La3Ga5SiO14:Eu) nano-powders were synthesized by a modified Pechini route and annealed in air at various temperatures between 750°C and 1000°C. Luminescence was excited at 365nm (transition 7F0→5D4). The dependence of the integral luminescence on the annealing temperature is very similar to that of the integral absorption (on the excitation transition). Increasing the thermal treatment temperature, a narrowing of the luminescence lines and a slight blue shift of the 5D0→7F0 line are observed. The lifetime of 5D0 level is in the 1 milisecond domain, while those of 5D1 and 5D2 levels are of the order of tens of microseconds and, respectively, microseconds. Our analysis shows that the decay of 5D0 is mostly radiative, the decay of 5D1 is controlled mainly by multiphonon processes, whereas the decay of 5D2 is governed by multiphonon and cross-relaxation processes. For comparison, a europium-doped langasite single crystal is also analyzed.