Kinetic Monte Carlo Model of Scintillation Mechanisms in CsI and CsI(Tl)

We have developed a computational model of energy transfer processes in scintillators using the kinetic Monte Carlo (KMC) approach. In this publication, we focus on the alkali halide compound CsI both pure and doped with a range of thallium concentrations. The KMC model makes use of an explicit atomistic representation of the crystal lattice, activator sites, defect sites, and individual electron-hole pairs. The probability of individual diffusion, recombination, and scintillation events is calculated from rate equations parameterized with data published in the literature. Scintillation decay curves, relative intensities of emission peaks, and light yields are computed and found to be in good agreement with experimental data for a range of temperatures and thallium concentrations. This demonstrates that the KMC scintillation model is capable of reproducing both the kinetics and the efficiency of the scintillation process in CsI. In addition, novel predictions emerge from our simulations such as the diffusion distance distributions of self-trapped holes and excitons. Finally, the KMC scintillation model provides a framework for probing possible physical processes responsible for the nonlinear relationship between scintillation light yield and incident gamma-ray energy.