Trapping and Recombination Centers in Cesium Hafnium Chloride Single Crystals: EPR and TSL Study

Abstract

Charge trapping phenomena and recombination centers were studied in three Cs2HfCl6 single crystals of slightly different stoichiometry grown by the vertical Bridgeman method. Electron paramagnetic resonance (EPR) spectra measured both before and after X-ray irradiation show creation of two distinct Vk centers. One of them was Vk(a) already known from a recent work by “R. Král, V. Babin, E. Mihoková, M. Buryi, V. V. Laguta, K. Nitsch, and M. Nikl, Luminescence and Charge Trapping in Cs2HfCl6 Single Crystals: Optical and Magnetic Resonance Spectroscopy Study, J. Phys. Chem. C 121, 12375–12382 (2017)”. Its quantity was different in each of the samples studied; the smallest, however, was in the one with the best stoichiometry. The second Vk center presently observed has never been described before. Its existence at an almost undetectable level was observed only in two of the three crystals. Thermally stimulated luminescence (TSL) spectra measured in the three samples were evidently composed of at least 2–3 strongly overlapped components within the 10–500 K temperature range. This suggested the existence of several recombination centers activated by the depletion of specific charge carrier traps. The corresponding TSL glow curves composed of seven complex peaks demonstrated significant decrease of the peaks amplitude in the sample with the best stoichiometry. Along with decreased radioluminescence amplitude, the combined EPR and TSL study allowed us to assume the reduction of both the recombination and trap center concentration with the increased crystal quality.