Annealing effects on the microstructure and photoluminescence of Eu3+-doped GdVO4 powders

This work explores the influence of annealing temperature on microstructure and optical characteristics of Eu3+ doped GdVO4 (0.5, 1, 2 and 3 at.% Eu3+) nanopowders produced via co-precipitation synthesis. Samples were annealed at different temperatures (300 degrees C, 600 degrees C, 800 degrees C and 1000 degrees C) for 2 h and XRD analyses confirmed their tetragonal zircon structure. As-synthesized powders were composed of nanorods (diameter similar to 5 nm, length similar to 20 nm) organized in bundles, which by annealing grew to faceted crystals of round and rectangular shape (50-150 nm in size). Energy band gap shifts to higher energy (3.56 eV -> 3.72 eV) with decreasing crystallite size (43 nm -> 13 nm). Photoluminescence emission spectra were recorded using two different excitation wavelengths: lambda(ex) = 330 nm and lambda(ex) = 466 nm, aiming to excite directly the host matrix and Eu3+ ions, respectively. The intensity of most pronounced red transitions is one order of magnitude higher for lambda(ex) = 330 nm due to a strong energy absorption of VO43- groups, followed by efficient energy transfer to Eu3+ ions. We investigated the influence of annealing temperature and concentration of Eu3+ ions on the optical properties, namely photoluminescence emission and excitation, and decay time. The maximum intensity of D-5(0) -> F-7(2) red emission is observed for sample treated at 1000 degrees C, containing 2 at.% of Eu3+ ions. With the increase of Eu3+ concentration (0.5-3 at.%) the decay time of D-5(0) -> F-7(2) transition decreases from similar to 1 ms to 0.5 ms. (c) 2013 Elsevier B.V. All rights reserved.