Abstract
AbstractIn several CaF2 single crystals grown by the Bridgman method and doped with CaO or in addition with SrF2 or NaF a luminescence band between 470 nm and 600 nm could be excited at 212 nm, its peak wavelength depending on the doping. With photo‐luminescence (PL) detected EPR five spin triplet centres were identified. Their axial fine structure constants D varied from 87 mT to 690 mT whereby the most intense spectra had the smallest D value. Theoretical calculations of the fine structure tensors and superhyperfine interactions show that the most intense and probable triplet centre consists of a pair of an OF– on a F– site next to a nearest neighbour F– vacancy which, compared to the well‐known F centre, is occupied by an excited electron in a shallow orbital and coupled to the 2p hole at the oxygen to form a S = 1 excited state. This centre can be excited optically at low temperature to a metastable new configuration where the F centre jumps into a 〈111〉 position opposite the OF–. The other triplet centres have probably also an O––F centre nearest neighbour configuration but have in addition a cation impurity or vacancy nearby. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
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