Petroff has examined several novel absorption bands produced by irradiating in the F-absorption band in additively colored alkali halide crystals. Specific models are given for the centers responsible for these absorption bands, and an interpretation of the photochemical and thermal transformations between these centers is presented. Trapping of electrons by dislocations and generation of pairs consisting of a positive and a negative ion vacancy at dislocations are discussed in detail. It is suggested that the clusters of vacancies, such as triplets or quartets, would not play a significant role, but the presence of dislocations should be of great importance in the photochemical processes. Many experiments are proposed which may provide a more stringent test of our models.
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