Metastable F Aggregate Color Centers in Irradiated KCl

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Abstract
The absorption spectra and decay lifetimes of the M center triplet state (3M) and R center quartet state (4R) measured in irradiated KCl are similar to previous results in additively colored crystals. The wavelength dependence of the light‐induced decay indicates that the 3M center is deactivated by illumination in its absorption bands at 505, 590, and 685 mμ (85°K), and pumped by illumination in the M1 band and also in the F band and K band regions. The initial yield of 3M centers induced by pulse illumination is proportional to the M center density, both for crystals of different initial F center density bleached to maximum M band and for a crystal that was bleached through the growth and decline of the M band. The temperature dependence of the dark decay follows a configuration coordinate model in which a transition of 45‐sec half‐time competes with a thermally‐activated step of 0.064 eV activation energy. The 14‐sec dark decay half‐time of the 4R center absorption at 710 mμ was found to be independent of temperature from 85° to 200°K. Possible mechanisms of metastable center formation and decay are discussed.

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