SITE-SELECTIVE SPECTROSCOPY OF PR3-ALUMINA CRYSTALS( IONS IN SODIUM BETA)

We report on the results of a low-temperature optical spectroscopy stu dy of Pr3+-exchanged sodium beta-alumina single crystals (Na+/Pr3+ bet a-Al2O3), containing different amounts of luminescent ions, in which e xcitation and fluorescence spectra have been carried out in sigma and pi polarization. The P-3(0)--> H-3(4) emission spectra, obtained under broad band excitation, show an intriguing structure consisting of sev eral components even with crystals containing low Pr3+ concentrations. The excitation spectra indicate the presence of at least two sets of different sites, available to Pr3+ in the conduction plane of beta-alu mina. Independently of the crystal composition, a quite satisfactory s ite-selective emission from each sets of centres has been achieved und er cw excitation of the 465.8 nm and 476.5 nm lines of an Ar+ ion lase r.