Luminescence and scintillation properties of CsI -- a potential cryogenic scintillator

TL;DR

This study investigates the luminescence and scintillation properties of CsI across a wide temperature range, providing insights into the underlying mechanisms and potential for cryogenic scintillator applications.

Contribution

It introduces a model explaining temperature-dependent luminescence changes in CsI based on self-trapped exciton dynamics and energy surface re-distribution.

Findings

Luminescence spectra vary with temperature due to exciton state populations.

The model explains the spectral changes through adiabatic potential energy surfaces.

Scintillation light yield's temperature dependence is analyzed via the Onsager mechanism.

Abstract

Caesium iodide is one of the more extensively studied scintillators. Here we present X-ray luminescence spectra, scintillation light output and decay curves as 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-centre 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-centre STE. The temperature dependence of the scintillation light yield is discussed in the framework of the Onsager mechanism.