Effect of the activator impurity on the scintillation yield in alkali‐halide crystals

, Phone: þ38(057) 341-01-67, Fax: þ38(057) 340-44-74The influence of different activator impurities on thescintillation yield of alkali halides has been investigated as afunction of temperature. Luminescence spectra of pure andactivated CsI and NaI scintillation crystals were measuredunder X-ray and VUV excitation at temperatures from 10 to300K. Inindium- andthallium-doped crystals activatorcenterscan capture electrons. Along with self-trapping of holes at lowtemperatures, electron capture by the dopant results in energystorage. This leads to a significant decrease of luminescenceyield. In Eu-doped NaI and CsI crystals activator centerscapture a hole first. In this way, at low temperatures electronsrecombine either with self-trapped holes (yielding STEemission), or with holes trapped by the activator (giving riseto Eu emission band). No energy loss at low temperature isevident in CsI:Eu and NaI:Eu crystals.