Time-resolved optical spectroscopy of CsI(Tl) crystals by pulsed electron beam irradiation

Properties of the color and emission centers induced with an electron pulse beam at temperature within 80–300 K have been studied in CsI(Tl) crystals. It has been established by optical spectrometry with time resolution that initial color centers in this crystal are only Tl0 and Vk centers, which spontaneously recombine emitting visible light at 2.25 and 2.55 eV. It has been shown that the emission decay kinetics at 80 K include two fast exponential components with decay constants 3 and 14 μs as well as slow hyperbolic component with the power index depending on the wavelength of the emitting light. The temperature effect on the emission kinetics has been studied and it has been directly proved that the emission rise stage at the temperature above 170 K is caused by the recombination of electrons, which are thermally released from single Tl0 centers, with VkA centers. The origin of scintillations in CsI(Tl) crystal is discussed in terms of the tunnel electron transitions from ground state of Tl0 centers to ground state of Vk centers at different distances from each other.