First principles computation study of Ce scintillation in YI3

Reports on high light output in yttrium triiodide doped with cerium in combination with its high stopping power, make this compound a good candidate for a successful scintillation detector. We present a thorough theoretical analysis of the processes that occur in YI3:Ce during scintillation. Our method includes first principles electronic structure calculations for the cerium-doped compound using density functional based methods to determine the positions of the 4f and 5d states relative to the valence and conduction bands of the host materials. This method has been developed as an integral component of a High Throughput Scintillator Discovery facility based at the Lawrence Berkeley National Lab. The method has been used for over 70 different compounds doped with cerium and shown to have consistent correspondence with experiment and good predictive power. In addition to the ground state calculations, we simulate excited state (Ce3+)* by constraining the occupancy of states so that it mimics the excitation. In this work, we report the results of host crystal energy gap computation, ionic relaxation for cerium-yttrium substitution, density of states calculated for ground state and excited state cases, Stokes shift relaxation, and the spatial distribution of the excited state wave function. Previously, we have established that the scintillation luminosity is influenced by the combination of the following parameters: (1) the size of the host material bandgap, (2) the energy difference between the valence band maximum of the host material and the Ce 4f level valence, and (3) the level of localization of the (Ce3+)* electron state on the Ce atom. All three of these parameters have been calculated for YI3:Ce and are in full correspondence with high luminosity reported for this compound.