Bleaching of F-Centers and Formation of Complex Centers in Gamma-Irradiated KCl at Room Temperature

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Abstract
The optical bleaching of F centers in gamma-irradiated KCl at various dosage was measured. The amount of F centers which bleached quickly, denoted by N q , was studied as a function of irradiation dose and bleaching temperature. It was found that N q includes the decrease of F center concentration due to complex center formation and due to recombination with positive holes, that the latter part of N q is closely related to the F centers formed in the first stage of gamma-irradiation, and that the complex centers are only formed by the bleaching of F centers formed in the second stage of irradiation. The rate of complex center formation by intermittent light pulses was studied, the results indicating that the amount of complex centers formed by a given number of pulses depends on the time interval between successive light pulses. The relaxation time for the formation of complex center was obtained at various temperatures from these results, and the activation energy (0.95±0.2) eV was obtained. An analysis of quickly bleached part of F center was tried taking the facts into consideration that F center formed in the first stage and the second stage of irradiation have quite different bleaching character and that complex center are formed after some ionic processes when second stage F center are bleached.