Bleaching and Recovery ofFCenters in KCl

Abstract

$F$ centers in KCl are optically bleached at room temperature with a minimum light energy of 20.1±1.0 ev per $F$ center. The $F$ band is recovered on further room-temperature x raying with a minimum energy of 69±5 ev per $F$ center. The increase in the $M$ and $R$ bands during optical bleaching of the $F$ band is nullified upon the recovery of the $F$ band by further x raying. The recovery kinetics are of second order in the number of optically bleached $F$ centers with a rate-constant of $(7.9\mathrm{}\pm 0.8)\times {10}^{-20\mathrm{}} {\mathrm{cm}}^3/F$ center-sec. The rate law requires an energy transfer from the bulk lattice and is consistent with an exciton mechanism.