F-H Center Formation by the Optical Conversion in Self Trapped Excitons in KCl Crystal

Abstract

The formation of F and H centers under the double excitation by a pulsed electron beam and a Q-switched ruby laser has been observed in KCl crystals between 5 K and 16.5 K. The efficiency of the F center formation due to the conversion of the self trapped exciton ( STE ) from the 3 Σ u + (σ u ,1 s σ g ) state to a higher state, possibly to the \(^{3}\varPi_{g}(\sigma_{u},2p\pi_{u})\) state, is as high as 0.35∼0.50 in this temperature range, and the efficiency of the back conversion \(^{3}\varPi_{g}{\rightarrow}{^{3}\varSigma_{u}^{+}}\) is very small. This small efficiency suggests a process faster than the \(^{3}\varPi_{g}{\rightarrow}{^{3}\varSigma_{u}^{+}}\) transition, supporting fast formation time of F centers (11±9 ps) in KCl. Rest of the STE , i.e. 65%∼50% of them, appear to go down to the ground 1 Σ g + state nonradiatively. A possible formation process of F and H centers is discussed.