Theory of F centres in alkaline earth fluorides

The point symmetry of the anion site in alkaline earth fluorides is T 3d and the F centre (an electron in an anion vacancy) in these crystals lacks inversion symmetry. Point ion calculations have been performed for the F centre in alkaline earth fluorides with trial functions of sufficient flexibility to incorporate the anisotropy of the potential. The predicted strong admixture of s and f orbitals in the ground Gamma 1 state yields calculated fluorine hyperfine interactions in substantial agreement with results of Endor measurements. An even stronger admixture of p and d orbitals in the first excited state leads to a linear Stark effect and the magnitude of this effect has been calculated for the F band. Experimental investigation of the Stark effect of the F band in SrF 2 provides an upper bound to the linear Stark splitting which is consistent with the predicted value. The quadratic Stark effect is discussed.