Colour Centres in Alkali Metal Doped SrF₂

Abstract

Colour centres in SrF2:Na+ and SrF2:K+ are studied by optical spectroscopy, magnetic circular dichroism (MCD) and by EPR. It is shown that, in each of these two materials, there exist two kinds of FA centres, the weakly perturbed F A(1) and the more strongly perturbed F A(2). The improperly named F2A centre is paramagnetic and its MCD has no similarity at all with the one of the F2 centre in SrF2. In SrF2:A+, non paramagnetic colour centres of the “F 3A+“ type are observed, as in CaF2:A+, but no defect corresponding to the f centre of CaF2:Na+. On the other hand, in SrF2:Na+ can be produced a centre which is called c', comparable to “F 3A+“, but with a spectral shift toward shorter wavelengths.

A Theoretical Investigation about the “F” Centre in MeF2:A+ (MeCa, Sr; ALi, Na, K)

“…Thus the [(ground 'El) -+ (lo:) ( 0 : ) ' X : ] transition should effectively be observed as the first intense absorption band of symmetrical, linear FIA centres, with its excited state non-degenerate. 4, The corresponding result for the [(ground 'El) + ( a : ) (x,) 'nu] transition is non-zero because of configuration mixing which introduces some ( 0 " ) ' wave function into (ground 'Z,'). We did not perform a precise calculation, but we estimated that the square of the dipolar matrix element toward ( a : ) ( 7~~) 'II, is one order of magnitude smaller than toward (lo;) ( 0 : ) ' Z:and (lo;) (K,,) 'nu.…”