Abstract
The emission spectra of the F center by irradiation into F, K, L1, L2 and L3 bands have been observed in KCl, KBr and KI crystals additively colored. The peak positions and the half widths of the emission band by the L1 light excitation were 1.21 eV, 0.26 eV; 0.96 eV, 0.21 eV; 0.88 eV, 0.14 eV in KCl, KBr and KI crystals, respectively, at liquid helium temperature, which were almost the same as those by the K or F light excitation. The ratio of the quantum yield of the emission by the L light to that by the F light, ηL⁄ηF, was between 0.44 and 0.83 in crystals examined. The emission intensity by the L band excitation dropped at temperatures above 100°K, 80°K and 60°K in KCl, KBr and KI crystals, respectively. This behavior of the emission intensity is similar fashion to that by the F light excitation. These results suggest that at low temperatures some of conduction electrons originating from either F or F′ centers by the stimulation into the L bands are captured at negative ion vacancies to form F* centers. Then, F* centers emit the ordinary F emission with the electronic transition to the ground state.
