In several CaF2 single crystals grown by the Bridgman method and doped with

CaO or in addition with SrF2 or NaF a luminescence band between 470nm and

600nm could be excited at 212nm, its peak wavelength depending on the doping.

With photo-luminescence-detected EPR five spin triplet centres were identified.

Their axial fine structure constants D varied from 87 to 690mT whereby the most

intense spectra had the smallest D value. Theoretical calculations of the fine

structure tensors and superhyperfine interactions showed 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, was 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.

Luminescence-Detected EPR of Oxygen-Fluorine Vacancy Complexes in CaF2.

U.Rogulis, R.C.Baetzold, J.M.Spaeth: Physica Status Solidi B, 2009, 246[5], 1099-

104