A. Bessière, P. Dorenbos, C. W. E. van Eijk, L. Pidol, K. W. Krämer and Hans U. Güdel
Spectroscopy and anomalous emission of Ce doped elpasolite Cs₂LiYCl₆
J. Phys.: Condens. Matter, 16, 1887-1897 (2004)                 

Abstract: A 10 ns fast luminescence was observed at 270 nm in Cs₂LiYCl₆:Ce³⁺ in addition to the 5d_t–4f Ce³⁺ doublet emission at 370 and 405 nm. This anomalous luminescence occurs exclusively for an excitation of the 4f–5d_e transitions of Ce³⁺ around 210 nm. It is not excited under across band gap excitation which makes it an uncommon phenomenon. The emission shows a large Stokes shift of 1.2 eV that must be related to an excited state with a very strong electron–lattice interaction or possible involvement of conduction band states. The 270 nm emission undergoes thermal quenching between 140 and 250 K while the 5d_t–4f Ce³⁺ emission gains intensity. The shape of the decay time spectra of the 5d_t–4f Ce³⁺ emission reflects a temperature activated transfer from the anomalous state to the 5d_t lowest Ce³⁺ level.