A. P. A. Marques

Rietveld refinement, cluster modelling, growth mechanism and photoluminescence properties of CaWO4:Eu3+ microcrystals

CaWO4:Eu3+ microcrystals (with 0, 1, 2 and 4 mol% Eu3+) were synthesized by a co-precipitation (CP) method and grown in a microwave-assisted hydrothermal (MAH) system at 130 °C for 30 min. X-ray diffraction (XRD), Rietveld refinement, X-ray absorption near edge spectroscopy (XANES), Fourier-transform Raman (FT-Raman) and Fourier-transform infrared (FT-IR) spectroscopy indicated that all of the microcrystals have a scheelite-type tetragonal structure without deleterious phases. Structural refinement data were employed to model the [CaO8], [EuO8] and [WO4] clusters. XANES spectra confirmed that the presence of deltahedral [EuO8] clusters promotes small distortions of neighbouring tetrahedral [WO4] clusters in a global tetragonal lattice. Field emission scanning electron microcopy (FE-SEM) images revealed that the replacement of Ca2+ by Eu3+ ions changed the particles shapes, resulting in the different morphologies of the microcrystals. UV-vis diffuse reflectance spectra indicated a reduction in the optical band gap with the replacement of Ca2+ by Eu3+ ions. The photoluminescence (PL) properties of the Eu3+ ions in CaWO4 were studied as well as the chromaticity coordinates and lifetimes of these compounds.

Effect of calcium on the structural properties of Ba(1−x)CaxTiO3 particles synthesized by complex polymerization method

Ferroelectric materials, such as barium titanate (BaTiO3), have been extensively studied for application in electronic and optical devices. The substitution of Ba by Ca is an effective method to improve the piezoelectricity temperature stability, as it can greatly lower the tetragonal–orthorhombic phase transition temperature, whereas the change of the Curie point is negligible. Ba(1−x)CaxTiO3 (xxa0=xa00, 0.05, 0.10, 0.15, and 0.20) powders were prepared by complex polymerization method. The effect of calcium on the tetragonality of the BaTiO3 system was monitored using basic characterization techniques: X-ray diffraction, differential scanning calorimetry, and Raman spectroscopy. The results indicate that increased calcium contents raise the Curie temperature (Tc) and that the addition of calcium in the BT matrix reduces tetragonality.

Effect of different starting materials on the synthesis of Ba 0.8 Ca 0.2 TiO 3

Literature has reported the synthesis of barium calcium titanates by various synthesis methods such as solid state reaction, co-precipitation and polymer precursors. These compounds are usually obtained using calcium carbonate (CaCO3), barium carbonate (BaCO3) and titanium oxide as starting materials. This study investigated the effect of different starting reagents on the synthesis of Ba0.8Ca0.2TiO3 (BCT) by complex polymerization method (CPM). Two sets of starting precursors were used: titanium citrate, CaCO3 and BaCO3, and titanium citrate and Ba1−xCaxCO3 solid solution precursor. Samples were crystallized at a temperature range from 400 °C to 700 °C for different time. The obtained powders were characterized by X-ray diffraction (XRD), thermogravimetry (TG) and differential thermal analysis (DTA), and Raman and infrared spectroscopy. The infrared spectroscopy indicated that the chelation processes of Ba, Ca, Ti and CA ions are very similar. The results showed that the use of CaCO3 and BaCO3 or Ba1−xCaxCO3 solid solution as precursors does not affect the final properties of BCT powders obtained by CPM.

Optical Characterization of Europium-doped Indium Hydroxide Nanocubes Obtained by Microwave-Assisted Hydrothermal Method

Crystalline europium-doped indium hydroxide (In(OH)3:Eu) nanostructures were prepared by rapid and efficient Microwave-Assisted Hydrothermal (MAH) method. Nanostructures were obtained at low temperature. FE-SEM images confirm that these samples are composed of 3D nanostructures. XRD, optical diffuse reflectance and photoluminescence (PL) measurements were used to characterize the products. Emission spectra of europium-doped indium hydroxide (IH:xEu) samples under excitation (350.7 nm) presented broad band emission regarding the indium hydroxide (IH) matrix and 5D0 → 7F0, 5D0 → 7F1, 5D0 → 7F2, 5D0 → 7F3 and 5D0 → 7F4 europium transitions at 582, 596, 618, 653 and 701 nm, respectively. Relative intensities of Eu3+ emissions increased as the concentration of this ion increased from 0, 1, 2, 4 and 8 mol %, of Eu3+, but the luminescence is drastically quenched for the IH matrix.

Structural investigation and photoluminescent properties of ZnWO4:Dy3+ nanocrystals

In this study, ZnWO4:Dy3+ nanocrystals containing 0.5, 1, and 2xa0mol% of Dy3+ were synthesized by a coprecipitation method and grown in a microwave-assisted hydrothermal system at 140u2009°C for 1xa0h. X-ray diffraction, Rietveld refinement, and Fourier transform Raman and infrared spectroscopy analyses indicated that each of the crystals had a wolframite-type monoclinic structure, with no other phases present. Structural refinement was carried out to model the distorted octahedral [ZnO6], [DyO6], and [WO6] clusters. Furthermore, transmission scanning electron microscopy images revealed interesting crystal morphologies and a decrease of the average crystal size, which were dependent on the Dy3+ doping concentration. Ultraviolet–Visible diffuse reflectance spectra indicated that the optical band gap increases with increasing replacement of Zn2+ by Dy3+ ions. The photoluminescent properties, chromaticity coordinates, and lifetimes of the ZnWO4:Dy3+ nanocrystals were studied.

Novel Gd(OH)3, GdOOH and Gd2O3 Nanorods: Microwave-Assisted Hydrothermal Synthesis and Optical Properties

We present a study of the controlled synthesis and optical properties of single-crystals Gd(OH)3, GdOOH and Gd2O3 nanorods. In this work, Gd(OH)3 nanorods were synthesized by a simple and fast microwave-assisted hydrothermal method. This process combined with the thermal decomposition oxidation of Gd(OH)3 nanorods as precursors enabled the preparation of single-crystalline GdOOH and Gd2O3 structures with well-defined morphology at low temperatures. The crystal structure dependence on the optical properties was investigated. We observed a green shift effect on the photoluminescence (PL) emission spectra from Gd(OH)3 to Gd2O3 nanorods, which can be attributed to different types of surface defects, as well as intrinsic properties that contribute significantly to the modified PL behavior.

Structure, Morphology, and Optical Properties of (Cal(1-3x)Eu(2x)) WO4 Microcrystals

In this letter, we report the efficient, surfactant-free, microwave-hydrothermal method of synthesizing calcium europium tungstate [(Ca1−3xEu2x)WO4, x = 0, 0.05, 0.01, 0.02, and 0.04] microcrystals. The structure and morphology were investigated using X-ray diffraction (XRD), Fourier-transform Raman (FT-Raman) spectroscopy, and field emission scanning electron microscopy (FE-SEM). XRD patterns and FT-Raman spectra indicated that all (Ca1−3xEu2x)WO4 microcrystals has a scheelite-type tetragonal structure. FE-SEM images revealed that the Eu3+ ions systematically affect the crystal shape and that there are two different types of superstructures: rice- and dumbbell-like microcrystals. The photoluminescence emission of the doped microcrystals changed relative to that of pure CaWO4 owing to the presence of defects and new energy levels associated with the Eu3+ content, which promotes the appearance of intermediate electronic levels in the band gap.