Laser-selective excitation, and fluorescence and Zeeman infra-red absorption spectroscopy, were used to study Sm3+ centers in doped crystals. The predominant center which was present in both crystals was found to consist of a C4v-symmetry Sm3+-F- pair. A weakly fluorescing non-locally charge-compensated Sm3+ ion center was also observed. These centers had cubic symmetry. In the case of CaF2:Sm3+, absorption features at 17809 and 17828/cm yielded no visible fluorescence upon resonant excitation. These transitions were associated with anion excess dimer and trimer centers where the Sm3+ optical excitation was completely quenched by non-radiative cross-relaxation energy transfer. Co-doping with La3+, Ce3+, Gd3+ or Tb3+ ions created heterogeneous clusters from which Sm3+ fluorescence was observed. In the case of co-doping with Eu3+, efficient and complete Sm3+(4G5/2)-->Eu3+(5D0) energy transfer occurred via multi-phonon assisted processes. Treating the crystals with O yielded C3v-symmetry centers that were associated with O2- charge compensation. Crystal- and magnetic-field analyses of the Oh and C4v symmetry centers yielded optimized crystal-field parameters which were consistent with those of other rare-earth ions and which could account for the magnetic splitting measured by Zeeman infra-red absorption.

Polarized Laser-Selective Excitation and Zeeman Infrared Absorption of Sm3+ Centers in CaF2 and SrF2 Crystals. J.P.R.Wells, R.J.Reeves: Physical Review B, 2000, 61[20], 13593–608