Channels of Energy Losses and Relaxation in CsI:A Scintillators (${\rm A}={\rm Tl}$, In)

Radiative relaxation channels and energy losses in In and Tl doped CsI scintillation crystals have been investigated as a function of temperature and excitation conditions to evaluate scintillation efficiency of the activator channel. Two activator concentration series of crystals were grown by the Bridgman method. Temperature dependence of excitation and luminescence spectra were measured under VUV and X-ray excitation; thermostimulated luminescence was also studied. The observed drop of radioluminescence yield of doped CsI crystals at room temperature relative to the pure crystal is explained by the migration losses caused by charge carrier trapping on the activator centers. The energy losses in CsI:A at low temperatures are due to the trapping of charge carriers on different centers: self-trapping of holes and capture of electrons by the activator centers. We suppose that migration energy losses are the main reason for significantly lower luminescence yield of CsI:A at room temperature than that of self-trapped excitons in pure CsI crystal.