The F3centre in alkaline earth fluorides. I

Abstract

A zero-phonon line has been observed in additively coloured CaF₂ at 677-4 nm and in additively coloured SrF₂ at 769.2 nm with an associated broad absorption band on the high energy side. The broad band shows a partly resolved phonon structure related to the single phonon density of states of the crystal. The zero-phonon line and associated broad band are also observed in fluorescence. The excitation spectrum for the fluorescence has been investigated. It is suggested that the centre giving rise to the spectrum is an F₃ complex composed of three nearest neighbour F centres aligned along (100). It is shown that the F₃ complex may be reoriented by linearly polarized bleaching light.