Jpr. Wells et Rj. Reeves, Polarized laser-selective excitation and Zeeman infrared absorption of Sm3+ centers in CaF2 and SrF2 crystals, PHYS REV B, 61(20), 2000, pp. 13593-13608
Laser-selective excitation and fluorescence and Zeeman infrared-absorption
spectroscopy have been employed to study Sm3+ centers in doped CaF2 and SrF
2 crystals. The dominant center present ih both host crystals has been dete
rmined to consist of a C-4 upsilon symmetry Sm3+-F- pair. A weakly fluoresc
ing, 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 excitatio
n. These transitions are associated with anion excess dimer and trimer cent
ers of which the Sm3+ optical excitation is entirely quenched through nonra
diative cross relaxation energy transfer. Codoping the crystals with La3+,
Ce3+, Gd3+ or TD3+ ions creates heterogeneous clusters from which Sm3+ fluo
rescence 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 compensatio
n. Crystal- and magnetic-field analyses of the O-h, and C-4 upsilon symmetr
y centers gives optimized crystal-held parameters which are consistent with
those of other rare-earth ions and which well account for the magnetic spl
itting measured by Zeeman infrared absorption.