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The time delayed double excitation spectroscopy has been utilized to determine the conversion ratio to F-H center pairs from self-trapped excitons(STEL) at the lowest state (1ss`g;a1g). The final conversion ratios, ηF/(ηF+ηX), were 0.86, 0.49 and 0.20 for NaCl, KCl and RbCl at 14K, respectively. The conversion efficiency (η =ηF+ηX) from STEL to F-H center pairs(ηF) and to unknown states(ηX) were 0.25, 0.90 and 0.76 for the hole excitation to πg, while 0.03, 0.01 and 0.01 for the electron excitation to b1u, b2u or b3u, in NaCl, KCl and RbCl, respectively.

Photobleaching effects on radiation-induced absorption in silica glass have been studied in a spectral range from 1.5 to 6.5 eV. The broad absorption induced by γ-ray exposure on chlorine-containing silica glass was fractionally decomposed with light illumination by successive change of photon energies from 1.6 to 5.0 eV. The decomposed spectra show that the γ-ray induced absorption consists of nine Gaussian component bands with the peak energy of 2.2, 2.6, 3.1, 4.0, 5.0, 5.1, 5.5, 5.8, and 6.2 eV. Photobleaching effects observed in the ESR spectra suggest that the 2.6 or 3.1 eV band originates from chlorine atoms generated by γ-ray exposure on the glass. From the correlative bleaching behaviors of the respective bands, the possible origins and their formation mechanism are discussed.