Luminescence and Color Center Foramation by the Optical Conversion of STE in KBr and NaCl

The optical conversion of self trapped excitons ( STE ) from 3 Σ + u state to 1 Σ + u state has been confirmed by observing the σ emission spectra in KBr and NaCl single crystals under the double excitation by a pulsed electron beam and a Q-switched ruby laser light. The conversion efficiencies are 0.3±0.1 and 0.6±0.1 for KBr (5.8 K) and NaCl (6.5 K), respectively, and decrease at higher temperatures. From their temperature dependence, thermal activation energies for the quenching of the conversion are estimated to be 5±1 meV (KBr) and 11±2 meV (NaCl). The conversion efficiency from the STE to the F centers is 0.7±0.2 in KBr. Possible relaxation process of the STE is discussed.