Theoretical investigations on the high light yield of the LuI3:Ce scintillator

The extremely high scintillation efficiency of lutetium iodide doped by cerium is explained as a result of at least three factors controlling the energy transfer from the host matrix to activator. We propose and theoretically validate the possibility of a new channel of energy transfer to excitons and directly to cerium, namely the Auger process when Lu 4f hole relaxes to the valence band hole with simultaneous creation of additional exciton or excitation of cerium. This process should be efficient in LuI3, and inefficient in LuCl3. To justify this channel, we perform calculations of density of states using a periodic plane-wave density functional approach. The second factor is the increase of the efficiency of valence hole capture by cerium in the row LuCl3–LuBr3–LuI3. The third one is the increase of the efficiency of energy transfer from self-trapped excitons to cerium ions in the same row. The latter two factors are verified by cluster ab initio calculations. We estimate either the relaxation of these excitations and barriers for the diffusion of self-trapped holes (STH) and self-trapped exciton (STE). The performed estimations theoretically justify the high LuI3:Ce3+ scintillator yield.