Probing of inversion symmetry site in Eu3+-doped GdPO4 by luminescence study: Concentration and annealing effect

Eu3+-doped gadolinium orthophosphate (GdPO4) (Eu3+ at%=0, 2, 5, 7, 10, 15, 20 and 30) nanoparticles have been prepared by ethylene glycol route and subsequently heated at 500 and 900 deg. C. The crystallite size increases with increasing heat-treatment temperature. Luminescence study shows that magnetic dipole transition (5D0→7F1) is prominent over the electric dipole transition (5D0→7F2), which has been attributed to occupancy of inversion symmetry site by more Eu3+ ions in Eu3+-doped GdPO4. The luminescence intensity is enhanced as heat-treatment temperature increases from 500 to 900 deg. C due to the improved crystallinity. Optimum luminescence is observed for 5-7 at% Eu3+ in GdPO4 nanoparticles. Above this concentration, luminescence intensity decreases due to concentration quenching effect. This is supported by lifetime study.