Effects of melt aging and off-stoichiometric melts on CsSrI3:Eu2+ single crystal scintillators

Abstract

Ternary halide scintillators are commonly prepared from a mixture of commercially available binary halides. The initial binary halides may contain excess halogen ions or have different volatilities, which could lead to loss of stoichiometry of the resulting ternary halide crystals and potentially negatively affect optical and scintillation properties. In this work, the effects of vacuum aging of the melt (melt aging) and use of off-stoichiometric melts via introduction of excess CsI on the crystal quality and scintillation properties of CsSrI₃:Eu²⁺, a promising scintillator for gamma-ray detection applications, are investigated. The phase purity of the grown samples was confirmed by powder X-ray diffraction and differential scanning calorimeter measurements, and the existence of matrix composition variations is revealed by energy-dispersive X-ray spectroscopy analyses. An abnormal relationship between the full energy peak and the shaping time, i.e. full energy peak broadening or existence of two full energy peaks, in the melt-aged and off-stoichiometric samples is observed. It is ascribed to a slow scintillation decay event in a time scale between 15 and 50 μs. For the CsSrI₃:Eu²⁺ single crystal grown from a stoichiometric melt without melt aging treatment, an energy resolution of 5.0% at 662 keV and a light yield of 48 000 ± 2000 photons per MeV can be achieved at a size of 1.4 cm³.