Short-living absorption and emission of CsI(Na)

This paper investigates the short-living absorption and the emission of CsI(Na) under a pulsed electron beam (Ee=0.25 MeV, t1/2=15 ns and W=0.003...0.16 J/cm2). The bands of singlet self-trapped excitons, as well as Na0 and Vk color centers have been detected in the transient absorption spectrum of CsI(Na). It has been found that the activator luminescence spectrum, peaking at 3.0 eV, fits a Gaussian (Em=3.0 eV and FWHM=0.44±0.02 eV at 80 K) and remains the same at different time delays within 10-8-10-3 s. The decay kinetics of the 3.0 eV emission has one nanosecond exponential component and two microsecond ones with time constants 1.0 and 3.0 μs, which remain unchanged within 78-150 K. It is concluded that the activator emission is due to the radiative annihilation of sodium-perturbed two halide excitons from the non-relaxed singlet state. The pathways of such excitons creation are discussed. - Highlights: → 3.0 eV emission in CsI(Na) caused by Na+ perturbed exciton (I2=)* in singlet state. → Na+ perturbed exciton can be formed due to Na0-Vk tunnel electron transition. → Short interspace {Na0 and Vk} pairs cause two stages of exponential emission decay. → Long interspace {Na0 and Vk} pairs cause hyperbolic emission decay.