NONEQUIVALENT PR3+ CENTERS IN GD3GA15O12

The Pr3+ spectra of Gd3Ga5O12 Czochralski-grown crystals, investigated by absorption, site-selective excitation and emission and fluorescence decays, shows a complex structure. Besides the spectra assigned to Pr3+ in dodecahedral c sites (D-2 local symmetry), Pr3+ in other sites is also significant. An attempt to assign the most intense lines to structural defects is made. Three of the most intense satellite lines are assigned to a Pr3+(c) ion perturbed by a nearby non-stoichiometric defect (Gd3+ in octahedral a sites) whose concentration is estimated to be about 7%. The spectra for perturbed Pr3+ centres show additional lines connected with a reduction in local symmetry. Two other lines have been assigned to Pr3+(cPr3+(c) pairs. The P-3(0) emission decays are almost exponential with similar lifetimes, except one that presents a very strong quenching. This line has been assigned to strongly coupled Pr3+(c)-Pr3+(c) nearest-neighbour pairs. The influence of pair quenching on the relative quantum efficiency of P-3(0) emission is also estimated.