The halogen vacancy, Tl-activator, and Tl-bound excitons in CsI:Tl scintillator

Recent decades have witnessed a concerted effort toward the discovery of new inorganic scintillators with higher light yield and better proportionality. There has been remarkable success as judged by the number of new scintillators developed. Despite this progress, the traditional scintillators, such as Tl-activated CsI (CsI:Tl) featuring a simple binary basis in a cubic lattice, remain important. In this work, we revisit CsI:Tl, examining its electronic properties from a computational perspective. Specifically, the halogen vacancy is investigated as a suspected electron trap and its role in nonradiative loss of carriers. We also discuss the self-trapping behavior of electrons and holes near the Tl-activator and associated lattice deformations. Finally, we explore Tl-bound, triplet exciton configurations that are likely linked to the observed Tl-luminescence bands.