Na+, Li+ and cubic centres in rare-earth-doped CaF2 and SrF2

Go-doping of rare-earth (R3+)-doped CaF2 and SrF2 with LiF, NaF or KF enhan ces the concentration of single R3+ centres of cubic symmetry. C-2v centre are also produced in which the R3+ ions are charge-compensated by Li+, Naor K+ ions located in the nearest-neighbour Ca2+ or Sr2+ sites in the [1 1 0] direction. Infrared-absorption studies have been carried out for many R3 + co-doped crystals. The infrared-absorption lines of the cubic centres app ear as magnetic-dipole allowed transitions and Zeeman measurements confirm their cubic symmetry. Absorption lines of the Li+ and Na+ centres occur wit hin 10 cm(-1) of the cubic-centre lines and shift in going from Li+ to Naindicating different placements of these ions in the (1 10) position. (C) 2 000 Elsevier Science B.V. All rights reserved.