Color Center Formation and Bleaching in KCl and NaCl by Electron Pulse at 15°K

Abstract

Primary effects of ionizing radiation in alkali halides have been studied by the pulsed electron beam. In KCl, F and H centers are produced mainly by a fast process as reported previously. The half width of the F band, however, was ∼0.3 eV at ∼20 ns after the electron shot and decreased to ∼0.18 eV at ∼10 μS. The fast process as well as the wide half width of the F band suggest that the primary products are not negative ion vacancies and charged interstitials, but F and H centers. In NaCl most F centers are produced by a slow process within about 1 μS due to the trapping of an electron at a negative ion vacancy. Absorption bands considered to originate from triplet states of self trapped excitons are observed at 660 mμ and 610 mμ in KCl and NaCl, respectively. In connection with the decay time of these bands and with the growth time of the F band, mechanism of the F center formation is discussed.