Site-selective spectroscopy of Tm3+ centers in CaF2:Tm3+

By polarized laser selective excitation, two single Tm3+ ion centers of tetragonal (C-4v) and trigonal (C-3v) symmetry have been identified in CaF2:0.05%Tm3+. Both of these centers exhibit blue, violet, and ultraviolet upconversion fluorescence under red-dye laser excitation. Crystal-field analyses of their assigned energy levels and fluorescence lifetime data are presented. By Zeeman infrared-absorption spectroscopy, a further Tm3+ center of cubic symmetry is identified. Measurement of the line strength of its single infrared-absorption line provides a direct method of determining relative Tm3+ center concentrations. With deuteration treatment, two families of D- centers derived from the C-4v and C-3v centers appear. Energy levels for four of the D--modified C-4v centers are reported. [S0163-1829(97)00841-2].