Decay of the F– centre in some alkali halides

Abstract

The production and subsequent decay of the F^– centre in NaF, NaCI, KBr and KI has been studied by pulse radiolysis. The centre decays by a mixture of thermal and photolytic processes, with temperature-independent photolysis dominant at low termperature. The thermal decay exhibited frist order kinetic behaviour in all cases, with a rate constant which was independent of both the dose per pulse and the previous radiation history of the sample: this is used as evidence that decay is via thermal ionisation rather than the vacancy capture process postulated previously.

The temperature dependence of the rate constant leads to the following values for the Arrhenius activation energy: NaF: 1.5 ± 0.15, NaCl: 1.10 ± 0.04, KBr: 0.43 ± 0.03, KI: 0.47 ± 0.02 eV.