First-principles Studies of Trapping States Associated with Impurities and Native Defects in Halide Scintillator Phosphor Materials and their Impact on Optical and Gamma Ray Detection Properties

Halide scintillator phosphors doped with Ce or Eu are amongst the brightest known new gamma ray detector materials (e.g. LaBr₃:Ce, BaBrI:Eu, SrI₂:Eu). The complete scintillation process in these materials is poorly understood and in particular the role of trapping states associated with impurities and native defects. We have performed first principles studies based on GGA, hybrid functionals and the GW method in tandem with experiments to understand the role of defect states in improving or degrading the gamma ray detection properties of this class of materials. In particular we have looked at hole, electron and exciton trapping at defect states and their mobility in terms of transfer to the Ce or Eu activator and how that can explain the very different optical and gamma ray detection properties of this class of scintillator materials.