Luminescence and scintillation properties of CsI: A potential cryogenic scintillator

Caesium iodide is one of the most extensively studied scintillators. Here, we present X‐ray luminescence spectra, scintillation light output and decay curves as a function of temperature, from room temperature down to below 10 K. Features of the observed intrinsic luminescence are explained in terms of radiative recombination of on‐ and off‐center STE. A model permitting interpretation of the dynamics of luminescence changes in CsI with temperature is suggested. This model includes adiabatic potential energy surfaces (APES) associated with singlet and triplet states of self‐trapped excitons (STE) and explains the variation of the luminescence spectra with temperature as a result of re‐distribution in the population between on‐ and off‐center STE. The temperature dependence of the scintillation light yield is discussed in the framework of the Onsager mechanism.