A. Bessière, P. Dorenbos, C. W. E. van Eijk, K. W. Krämer, H. U. Güdel and A. Galtayries
Scintillation and anomalous emission in elpasolite Cs₂LiLuCl₆:Ce³⁺
J. Lumin. 117, 187-198 (2006)                 

Abstract: The luminescence and scintillation properties of Cs₂LiLuCl₆:0.5%Ce³⁺ are presented. Special attention is devoted to a 9.4 ns fast emission at 275 nm that can only be excited via the highest cubic field 5d_e state of Ce. Contrary to Cs₃LuCl₆ and Cs₂LiYCl₆, where the same type of fast emission was observed, the emission in Cs₂LiLuCl₆ is still observed at room temperature. Assuming that the 5d_e state is located inside the host conduction band (CB), we propose that the emission originates from a mixed state at or just below the bottom of the CB and ends at the 4f ground state of Ce³⁺. To proof this model we studied the thermal quenching of the anomalous luminescence and performed X-ray photoelectron spectroscopy. A model for a temperature-activated energy transfer from the anomalous state to the lowest 5d_t excited state of Ce³⁺ explains most of the results. Besides the 275 nm emission, the material shows 5d_t–4f Ce³⁺ emission at 370 and 406 nm and 2 ns fast core-valence luminescence when excited with 16–22 eV photons. The scintillation properties of Cs₂LiLuCl₆:Ce are briefly discussed.