Scintillation and anomalous emission in elpasolite Cs2LiLuCl6:Ce3+

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 5de 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 5de 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 5dt excited state of Ce3+ explains most of the results. Besides the 275 nm emission, the material shows 5dt-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.