Fabrication of polycrystalline (Y0.7Gd0.3)(2)O-3:Eu3+ ceramics: The influence of initial pressure and sintering temperature on its morphology and photoluminescence activity

Nanocrystalline (Y0.7Gd0.3)(2)O-3 powder, synthetised via polymer complex solution method, was compacted into 25 pellets applying high pressures (173-867 MPa) for 30 s that were subsequently sintered at different temperatures (800-1400 degrees C) for 18 h. The morphology and optical characteristics of the starting powder and prepared ceramic samples were monitored and discussed in order to identify the changes induced with the variations of initial compacting pressure, which influence is often neglected, and with sintering temperature. The grain size tends to decrease significantly with increasing pressure, even when elevated temperatures are used for annealing, while low compacting pressure resulted in grain coarsening and, in some cases, even in anomalous morphology of ceramic samples. Luminescence emission in ceramic samples decays faster than in nanopowders, that is in complete agreement with the grain formation and gradual transformation to the bulk material. Judd-Ofelt intensity parameters and branching ratios were calculated taking into account the difference in effective refractive index for nanopowder and ceramic samples. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved

Eu3+-doped (Y0.5La0.5)(2)O-3: new nanophosphor with the bixbyite cubic structure

New red sesquioxide phosphor, Eu(3+)doped (Y0.5La0.5)(2)O-3, was synthesized in the form of nanocrystalline powder with excellent structural ordering in cubic bixbyite-type, and with nanoparticle sizes ranging between 10 and 20 nm. Photoluminescence measurements show strong, Eu3+ characteristic, red emission (x = 0.66 and y = 0.34 CIE color coordinates) with an average D-5(0) emission lifetime of about 1.3 ms. Maximum splitting of the F-7(1) manifold of the Eu3+ ion emission behaves in a way directly proportional to the crystal field strength parameter, and experimental results show perfect agreement with theoretical values for pure cubic sesquioxides. This could be used as an indicator of complete dissolution of Y2O3 and La2O3, showing that (Y0.5La0.5)(2)O-3:Eu3+ behaves as a new bixbyite structure oxide, M2O3, where M acts as an ion having average ionic radius of constituting Y3+ and La3+. Emission properties of this new phosphor were documented with detailed assignments of Eu3+ energy levels at 10 K and at room temperature. Second order crystal field parameters were found to be B-20 = -66 cm(-1) and B-22 = -665 cm(-1) at 10 K and B-20 = -78 cm(-1) and B-22 = -602 cm(-1) at room temperature, while for the crystal field strength the value of 1495 cm(-1) was calculated at 10 K and 1355 cm(-1) at room temperature

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