Since the literature suggests sensitivity to impurities, material was obtained from more than one supplier. The single-crystal CsI samples used in this work were provided by the Harshaw Company, USA and the Zhongjing Company, Beijing, China. The samples were cut into slices with a thickness of 1mm for the RL and TL measurements. The spectra were recorded on the Sussex high-sensitivity wavelength multiplexed TL system, which has two detectors covering the wavelength ranges 200–480 and 480–800nm. (Therefore, there may be a trace in the figures of the matching point of the two detectors.) Signals with different wavelengths were recorded simultaneously with time steps of 3 s. Spectra were corrected for the spectral sensitivity of the recording system. The resolution used in this work was 5 nm. The X-ray irradiation was performed in vacuum at low temperature with an in situ Philips tungsten X-ray tube. The voltage and current used in this work were 11–40 kV and 4–15mA, respectively. The rate of both heating and cooling was 6 K/min. The integration time for data collection was unchanged when different voltages were used.