Polarized laser-selective excitation and Zeeman infrared absorption of Sm3+ centers in CaF2 and SrF2 crystals

Laser-selective excitation and fluorescence and Zeeman infrared-absorption spectroscopy have been employed to study Sm3+ centers in doped CaF2 and SrF2 crystals. The dominant center present ih both host crystals has been determined to consist of a C-4 upsilon symmetry Sm3+-F- pair. A weakly fluorescing, nonlocally charge-compensated Sm3+ ion center has also been observed. These centers have cubic symmetry. In CaF2:Sm3+, absorption features at 17 809 and 17 828 cm(-1) yield no visible fluorescence upon resonant excitation. These transitions are associated with anion excess dimer and trimer centers of which the Sm3+ optical excitation is entirely quenched through nonradiative cross relaxation energy transfer. Codoping the crystals with La3+, Ce3+, Gd3+ or TD3+ ions creates heterogeneous clusters from which Sm3+ fluorescence is observed. However, in the case of codoping with Eu3+, efficient and complete Sm3+((4)G(5/2)) --> Eu3+ (D-5(0)) energy transfer is observed through multi-phonon-assisted processes. Treating the crystals with oxygen yields C-3 upsilon symmetry centers associated with O2- charge compensation. Crystal- and magnetic-field analyses of the O-h, and C-4 upsilon symmetry centers gives optimized crystal-held parameters which are consistent with those of other rare-earth ions and which well account for the magnetic splitting measured by Zeeman infrared absorption.