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

Abstract

One of the most conspicuous colour centres in MeF, : A + (Me = Ca, Sr; A = Li, Na, K) is the so-called "Fe:,".It is investigated whether this centre may really be composed of three neighbouring fluorine vacancies, along a [0, 0, 11 direction, decorated by two electrons, with an alkaline impurity A + in the vicinity. This structure seems to be ruled out by a comparison of the experimental magnetic circular dichroism data of other authors with the results of present Hartree-Fock calculations of the energy levels of linear FiA centres in fluorite-like lattices. For this calculation, an H i hydrogen molecular ion model is used similar to the ones which have already proved efficient in several other colour centre problems.L'un des centres colores les plus importants dans MeF,:A+ (Me=Ca, Sr; A=Li, Na, K) est celui que I'on appelle "F:,". Nous examinons s'il peut gtre reellement constitub de trois lacunes de fluor voisines, alignkes le long d'un axe [0, 0, 11, decorees par deux electrons, avec une impureti alcaline A+ au voisinage. Cette structure semble exclue par la comparaison entre les donnees de dichroisme circulaire magnetique d'autres auteurs et les rksultats de notre present calcul Hartree-Fock des niveaux d'energie de centres lineaires F :, dans les reseaux de CaF, et SrF,. Nous avons utilise pour ce calcul un modele d'ion moleculaire hydrogene H i , analogue a ceux qui se sont deja reveles eficaces pour plusieurs autres problemes de physique des centres colores.

Photoluminescence studies of γ-irradiated CaF2:Dy:Pb:Na single crystals

“…This was attributed to the R þ A centre (also represented as F þ 3a centre) having a linear structure on the basis of polarization luminescence. Based on the results of magnetic circular dichroism and a suitable theoretical model it was suggested that the R þ A centre should have angular configuration rather than linear one [25]. Thus, the true structure of the centre giving rise to the absorption at 2.53 eV and emission at 2.23 eV is debatable.…”