Luminescence response of CsI:Na to electron pulse irradiation

This paper investigates the influence of activator concentration and temperature on the scintillation process in CsI:Na crystal which was excited by a pulsed electron beam (Eex = 0.25 MeV, t1/2 = 15 ns, W = 0.003…0.16 J/cm2) at temperature within 77–300 K. It has been established that the transition of Na-bound two halide exciton from singlet state causes 3 eV emission of CsI:Na. The capturing of Vk by Na+ ion determines the scintillation pulse shape. Thermal liberation of Vk from VkA centers results in an inertial rise of the emission pulse in lightly activated CsI:Na and in a mono-exponential decay of the emission pulse in heavily activated CsI:Na. The value of thermal dissociation energy of VkA centers is 0.24 ± 0.01 eV, which was obtained from the temperature dependences of the emission decay time constant for CsI:2.8∙10−3%Na and of the rise time constant for CsI:2.0∙10−4%Na.

► Processes of the energy transfer to emission centers in CsI:Na is explained.
► Mathematical description of the mechanism of energy transfer to activator emission centers is given.
► VkA thermal dissociation is the main factor in forming the scintillation pulse in CsI:Na.
► Activator emission centre in CsI:Na is Na-bound two halide exciton.