SITE-SELECTIVE SPECTROSCOPY OF TB3+ CENTERS IN SRF2 AND CAF2

Laser-selective excitation techniques have been used to establish sets of energy levels for both the fluoride and hydrogenic varieties of th e tetragonal symmetry (C-4 upsilon) centers and for five multihydrogen ic centers observed in SrF2:Tb3+ and CaF2:Tb3+. Infrared-absorption me asurements identified additional energy levels for the principal C-4 u psilon F- centers and crystal-field fits are reported for these. Polar ization studies of the various spectral lines of the C-4 upsilon F- ce nters were used to determine the symmetry labels of energy levels, up to the D-5(4) multiplet. Both electric- and magnetic-dipole contributi ons to the intensities of absorption and fluorescence lines need to be included to account for the observed polarization behavior. The multi hydrogenic ion centers exhibit varied forms of bleaching behavior asso ciated with light-induced hydrogenic ion motion. One center is strikin gly unusual as it increases in intensity on irradiation in the region of its D-5(4) multiplet transitions. D-5(4) multiplet fluorescence lif etimes are closely similar for the H- and D- varieties of all the hydr ogenic centers, indicating essentially radiative lifetimes.