Luminescence Properties of Redispersible Tb3+-Doped GdPO4 Nanoparticles Prepared by an Ethylene Glycol Route

Nanoparticles of Tb3+-doped GdPO4 (Tb3+ = 0, 2, 5, 7, 10, and 20 atom-%) have been prepared at a relatively low temperature of 160 degrees C in ethylene glycol medium. The particles crystallize in a monoclinic structure with an average crystallite size of 30-50 nm. From the luminescence study of Tb3+-doped GdPO4, the magnetic dipole transition (D-5(4)-> F-7(5)) at 545 nm (green) was found to be more prominent than the electric dipole transition (D-5(4)-> F-7(6)) at 484 nm (blue). Maximum luminescence intensity and lifetime was observed for 7 atom-% Tb3+. Above 7 atom-% Tb3+, a decrease in luminescence was observed. This has been attributed to a concentration-quenching effect due to the cross-relaxation among Tb3+ ions. The highest luminescence intensity of Tb3+ was observed after excitation at 274 nm (S-8(7/2)-> I-6(11/2) of Gd3+) among various excitation wavelengths (including f-f absorptions of Tb3+). This is due to an efficient transfer of energy from Gd3+ to Tb3+ that shows GdPO4 to be a potential host for Tb3+. These nanoparticles are found to be redispersible in water and ethanol and are incorporated into polyvinyl alcohol film homogeneously. This film showed bright green emission.