Non-equivalent Pr3+centres in Gd3Ga15O12

The Pr 3+ spectra of Gd 3 Ga 5 O 12 Czochralski-grown crystals, investigated by absorption, site-selective excitation and emission and fluorescence decays, shows a complex structure. Besides the spectra assigned to Pr 3+ in dodecahedral c sites (D 2 local symmetry), Pr 3+ 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 Pr 3+ (c) ion perturbed by a nearby non-stoichiometric defect (Gd 3+ in octahedral a sites) whose concentration is estimated to be about 7%. The spectra for perturbed Pr 3+ centres show additional lines connected with a reduction in local symmetry. Two other lines have been assigned to Pr 3+ (c)-Pr 3+ (c) pairs. The 3 P 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 Pr 3+ (c)-Pr 3+ (c) nearest-neighbour pairs. The influence of pair quenching on the relative quantum efficiency of 3 P 0 emission is also estimated.