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

Abstract

This work explores the influence of annealing temperature on microstructure and optical characteristics of Eu3+ doped GdVO4 (0.5, 1, 2 and 3at.% Eu3+) nanopowders produced via co-precipitation synthesis. Samples were annealed at different temperatures (300°C, 600°C, 800°C and 1000°C) for 2h and XRD analyses confirmed their tetragonal zircon structure. As-synthesized powders were composed of nanorods (diameter∼5nm, length∼20nm) organized in bundles, which by annealing grew to faceted crystals of round and rectangular shape (50–150nm in size). Energy band gap shifts to higher energy (3.56eV→3.72eV) with decreasing crystallite size (43nm→13nm). Photoluminescence emission spectra were recorded using two different excitation wavelengths: λex=330nm and λex=466nm, 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 λex=330nm 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 5D0→7F2 red emission is observed for sample treated at 1000°C, containing 2at.% of Eu3+ ions. With the increase of Eu3+ concentration (0.5–3at.%) the decay time of 5D0→7F2 transition decreases from ∼1ms to 0.5ms.