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In this work we studied the structural and optical properties of lithium tantalate (LiTaO3) powders doped with Eu3+ ions. We have examined the different sites occupied by the rare earth ion through the correlation of the DRX data analyzed with the Rietveld method and some spectroscopic parameters derived from the Eu3+ luminescence. A direct relation was established between the lattice parameters and the “occupation fraction” of Eu3+ in each LiTaO3 site. The occupation fraction was set as the relative population of Eu3+ ions for each site obtained by means of the intensity, baricenter, and the spontaneous emission coefficients of the 5D0→7F0 transitions. We concluded that the unit cell parameter a presents the same behavior of the Eu3+ occupation fraction in Ta5+ sites as a function of the Eu3+ content in LiTaO3. The same was observed for the variation in Eu3+ occupation fraction in the Li+ site and the unit cell parameter c with the Eu3+ content. [ABSTRACT FROM AUTHOR]

Abstract The present work reports on the synthesis, structural and optical properties of (Y 1-x Eu x) 4 Al 2 O 9 powders, with x ranging from 0.001 to 0.030. We prepared the materials using a modified polymeric precursors method, and the effect of annealing temperature and Eu3+ concentrations were evaluated. Structural and microstructural parameters, such as cell parameters, crystallite size and grain size were determined and evaluated by using the results from X-ray diffraction and high-resolution transmission electron microscopy techniques. An annealing temperature of 800 °C was enough to obtain single Y 4 Al 2 O 9 crystalline phase with good distribution of Eu3+ ions. Diffuse reflectance spectra and optical bandgap of 4.52 eV for (Y 0.995 Eu 0.005) 4 Al 2 O 9 – determined by Kubelka-Munk model – showed good optical quality of the samples, which were considered non-conducting. All doped samples possessed visible photoluminescence emission from Eu3+ ions under excitation at 393 nm, with higher emissions occurring in the red region from 5 D 0 → 7 F 2 transition, with R/O relation of 1.69 for the sample with x = 0.010. Analyzing photoluminescence emission spectra, the lifetime values and Judd-Ofelt parameters, we determined that Eu3+ occupied three different sites of the Y 4 Al 2 O 9 (YAM) structure, replacing Y3+ ions, with the quenching concentration occurring between x = 0.020 and x = 0.030. We noted that Eu3+ ions are in a chemical environment with low polarization, and their degree of covalence is low. Finally, samples with x = 0.020 (Y 0.980 Eu 0.020) 4 Al 2 O 9 seems to be useful as red phosphors. Graphical abstract fx1 [ABSTRACT FROM AUTHOR]

Abstract: Lead Titanate Zirconate (PZT) perovskite powders were synthesized by microwave hydrothermal method (M-H) at 180°C for different time periods (2, 4, 8 and 12h) with the presence of aqueous polyvinyl alcohol (PVA) solution 0.36gL−1. The X-Ray diffraction (XRD), SE-FEG as well as the measurements of photoluminescence (PL) emission were used for monitoring the formation of a perovskite phase with random polycrystalline distortion in the structure. Emission spectra with fixed excitation wavelength of 350nm showed higher value for the powder obtained after undergoing 8h of treatment. A theoretical model derived from previous calculations allows us to discuss the origin of photoluminescence emission in the powders, which can be further related to the local disorder in the network of both ZrO6 and TiO6 octahedral, and dodecahedral PbO12. The new morphology initially observed from the PZT perovskite crystal growth bearing the shape of fine plates is found to be directly related to photoluminescence emission with energy lower than that present in the PZT with cube-like morphology that emits in 560nm. [Copyright &y& Elsevier]

Abstract: This work reports the pure lithium tantalate (LiTaO3), europium (III)-doped LiTaO3 and magnesium (II)–europium (III)-doped LiTaO3 preparation by the polymeric precursor method, using four different powered samples of Eu3+ ion concentrations 0.1 and 1at%, observing their effect on the luminescent property of the material. Results indicated LiTaO3 phase free of secondary phases at 650°C and the photoluminescence (PL) emission spectra showed the characteristic sharp emission bands given by Eu3+ ions when they are excited at a wavelength of 399nm. An increase of dopants led us to a non-homogeneous broadening and showed a slightly larger one when Mg was added. A displacement of the transition 5D0→7F0 to shorter wavelengths as function of Eu3+concentration was also noticed. [Copyright &y& Elsevier]

Abstract: The synthesis, structure characterization, as well as luminescence properties of LaTaO4 ceramics were investigated in this study. The materials were prepared through the Pechini method. The characterization techniques, including the X-ray diffraction (XRD) as well as the scanning electron microscopy (SEM) were used to analyze the structure and microstructure, respectively. Details of emissions as a result of the type V O * (or V O **) defects were determined using photoluminescence (PL) measurements. [Copyright &y& Elsevier]

Tb 2 TeO 6 crystalline phase was prepared by solid-state reaction synthesis, presenting an orthorhombic structure with lattice parameters a = 5.2907(2) Å, b = 9.1079(30 Å, and c = 10.0113(3) Å. Thermal analysis measurements revealed two distinct thermal events, one of them associated to phase decomposition around 1230 °C and another more complex from 300 °C up to 1100 °C probably related to the Tb3+/Tb4+ oxidation reaction. The optical band gap was estimated to 4.36 eV. A high reflectance in the visible and near infrared regions was measured, as well the photoluminescence with bands centered at λ = 490, 548, 585, and 620 nm, attributed to electronic transitions of Tb3+ ions. [Display omitted] • The orthorhombic Tb 2 TeO 6 phase is stable until decomposition. • Tb 2 TeO 6 showed high emission at 548 nm (5D 4.→7F 5) characteristic of Tb3+ ions • Redox reaction occurs between 300 °C and 1100 °C. • The redox reaction is reversible under cooling but kinetically limited. • Remaining Tb+4 ions generate crystalline defects that disappear after aging time. [ABSTRACT FROM AUTHOR]

Abstract: Micro-cube-shaped lead zirconate titanate was synthesized using the microwave-assisted hydrothermal method. Photoluminescence and field emission scanning electron microscopy were used for monitoring the formation of mesocrystals. Based on these results, a growth mechanism was then proposed which involved nanoparticle aggregation, nanoplate self-assembly on specific architecture and the final formation of mesoscopic micro-cube-shaped lead zirconate titanate. [Copyright &y& Elsevier]