F Center Formation in KCl Crystals by Pulsed Electron Beam at 80°K

Abstract

The transient formation and decay of F centers in KCl crystals have been studied using a pulsed electron beam from a linear accelerator. The electron pulse has a 30 ns half width at 60 MeV and the maximum peak current is 1.2 amp. In “as received” crystals F center formation is of the fast type which takes place in very short time less than the pulse width and generated F centers bleach partially within ∼40 ns, probably due to the tunneling annihilation with H centers. In “irradiated” crystals which are discolored and bleached with white light, the F center formation consists of the fast and slow types. The slow type formation has a time constant of 0.60±0.02 μs at 80°K which is the same as the decay time of the F center luminescence. The slow type formation is, therefore, considered to take place when an electron is captured by an anion vacancy through the first excited state of the F center.