Fast 20 ns 5d–4f luminescence and radiation trapping in BaF2:Ce

Parity-allowed UV 5d–4f transitions characterized by a high oscillator strength make trivalent cerium an interesting activator for fast and efficient scintillator crystals. Indeed, several materials are known, in which the radiative lifetime of the Ce3+ ions is shorter than 20 ns (e.g. LuAlO3:Ce and YAlO3:Ce). For the case of BaF2:Ce, however, the value of 27 ns is known from literature. In this communication we show that the 5d–4f luminescence in BaF2:Ce is in fact faster. Having analyzed several series of time profiles recorded at various temperatures between 25 and 350 K, we conclude that the true radiative lifetime of the Ce3+ ions in BaF2 is close to 20 ns and it is the radiation trapping caused by the temperature-dependent reabsorption of cerium emission which prolongs the effective decay time.