Low temperature radioluminescence spectra of CsI:Tl

Four radioluminescence bands associated with thallium at 400, 488, 550 and 593 nm, plus an intrinsic band at 340 nm have been observed in the temperature range 280-25 K in CsI:Tl. The temperature dependence of the emission intensity is obviously different from each band to another. The 488, 550 and 593 nm bands are associated with the decay of different type thallium perturbed V_K-e excitons, respectively, and the 340 nm band is related with the unperturbed H-F excitons. It is suggested that V_K centres are also involved in the emission of the 400 nm photons. The re-absorption of the 488 nm signals and the resulting increase of the 593 nm band have been discussed. At 25 and 290 K, the relative RL intensities between the four thallium associated bands do not change with the X-ray tube voltage from 15 to 40 kV. But the intensity of the 340 nm band increases faster than that of the thallium related bands when the tube voltage increases.