F and perturbed F(F*) centres in strontium chloride

Point-ion and ion-size calculations on F centres and F* centres (F centres perturbed by an alkaline impurity) in SrCl 2 are described. The point-ion calculation for the F centre gives a transition energy of 2.11 eV (experiment 2.13 eV) and a hyperfine interaction with the hearest 35 Cl nuclei of 45.7 MHz (experiment 23.8 MHz). Ion-size calculations lead to an improved value for the hyperfine interaction. A model of the F* centre with an interstitial alkali ion in a second-neighbour position and associated distortions explains the observed optical absorption spectra.