F+2-center in potassium chloride crystals. - Part I : Formation and bleaching kinetics

Abstract

A quantitative analysis of the higher transitions of the M center in the UV at ¡Ü5.0 eV in KCl crystals with a high [M]:[F] ratio and unaligned and aligned M center shows several new excitations (LM bands). Assuming that the LM excitation leads to conductive states, a simple electron kinetic model shows that UV irradiation of the F + M center system produces ionized F and M center (¦Á and F2+) while competing capture processes partially destroy them or form F' and M' center. The F2+ center production spectrum should closely follow the absorption ratio of LM:LF while the bleaching spectrum should follow the F' and M' spectrum. Experimental confirmation of this model is presented. By x-raying the crystal (containing F + M centers) at LHeT, extra electron traps are introduced into the crystal and shift the equilibrium of the reaction to higher amount of F2+ center, which are not stabilized by F' and M' centers. These extra F2+ center anneal out near 40¡ãK in parallel with the 3rd stage annealing of x-ray produced ¦Á-center-interstitial anions.