First-principles Studies of Tl activated Scintillator Phosphor Materials: Towards an understanding of the Scintillation mechanism*

Tl doped halide scintillator phosphors are amongst the most commonly used gamma ray detector materials for medical imaging, high energy physics and nuclear materials detection applications (e.g. CsI:Tl, NaI:Tl). Even so the complete scintillation process in these materials is poorly understood. Recently there has been interest in co-doping these materials to try and improve their detection performance. We have performed first-principles studies based on GGA, hybrid functionals and the GW/BSE method in tandem with experiments to understand the scintillation mechanism in these materials and how it could be improved by co-doping. In particular we have looked at the Tl exciton optical emission states and energy transfer mechanisms from the gamma ray to the Tl. Recently there has also been interest in new Tl bulk scintillators such as TLYC (Tl₂LiYCl₆) which we have also studied.