Studies of first-stage F-centre production in alkali halides doped with strontium

KBr crystals doped with strontium have been X-irradiated at 293 K. The reduction in single impurity-vacancy dipole concentration has been measured using ionic thermocurrent techniques and is found to be proportional to and in quite close numerical agreement with F-centre growth in both first and second stage F-centre production, this being in agreement with previous results in KCl(Sr). The growth of the absorption band peaking at 263 nm was studied and was found to be proportional to F-centre growth during the earlier stages of colouration, indicating that the responsible centres are a major complement of the F-centres. Ionic conductivity experiments show little agreement between the decay of conductivity and the growth of F-centres during X-irradiation of KCl(Sr) crystals at 293 K. A model is developed in which interstitials are trapped at impurity-vacancy dipoles and in which the two stages of F-centre production is the result of dynamic processes involving modifications of the excitonic mechanisms or of back reactions. (author)