Microstructural and optical characterization of CaWO4 and SrWO4 thin films prepared by a chemical solution method

Stoichiometric CaWO4 and SrWO4 thin films were synthesized using a chemical solution processing, the so-called polymeric precursor method. In this soft chemical method, soluble precursors such as strontium carbonate, calcium carbonate and tungstic acid, as starting materials, were mixed in an aqueous solution. The thin films were deposited on glass substrates by means of the spinning technique. The surface morphology and crystal structure of the thin films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Nucleation stages and surface morphology evolution of the thin films on glass substrates were studied by atomic force microscopy. The films nucleate at 300 degreesC, after the coalescence of small nuclei into larger grains yielding a homogeneous dense surface. XRD characterization of these films showed that the CaWO4 and SrWO4 phases crystallize at 400 degreesC from an inorganic amorphous phase. No intermediate crystalline phase was identified. The optical properties were also studied. It was found that CaWO4 and SrWO4 thin films have an optical band gap, E-gap=5.27 and 5.78 eV, respectively, of a direct transition nature. The excellent microstructural quality and chemical homogeneity confirmed that this soft solution processing provides an inexpensive and environmentally friendly route for the preparation of CaWO4 and SrWO4 thin films. (C) 2003 Elsevier B.V. All rights reserved.

Ferroelectric materials with photoluminescent properties

Amorphous LiNbO3 thin films processed by polymeric precursor method exhibited efficient luminescence at room temperature. The films were deposited on silicon substrates and treated at 200degreesC for different times. The photoluminescence emission yield decreases with the increase of the treatment time and disappears for crystalline films. A theoretical-experimental study was performed on amorphous and crystalline materials to understand the influence of the defects on the photoluminescence properties. The theoretical band gap obtained by the difference of energy between the HOMO and LUMO levels is larger for crystalline structure when compared with amorphous material. This result, which is in agreement with experimental band gaps obtained from optical measurements, revealed the emergence of new electronic levels for the amorphous material, which are localized in the wide band gap of the crystalline structure. These new electronic levels may explain the photoluminescence observed at room temperature for LiNbO3 amorphous films.

Structural Refinement and Photoluminescence Properties of MnWO4 Nanorods Obtained by Microwave-Hydrothermal Synthesis

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of Different Solvent Ratios (Water/Ethylene Glycol) on the Growth Process of CaMoO4 Crystals and Their Optical Properties

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Synthesis, growth process and photoluminescence properties of SrWO4 powders

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Wettability and photodegradation activity of sol-gel dip-coated zinc oxide films

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Synthesis, structural refinement and optical behavior of CaTiO3 powders: A comparative study of processing in different furnaces

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Synthesis, ferroelectric and optical properties of (Pb,Ca)TiO3 thin films by soft solution processing

Calcium modified lead titanate sol was synthesized using a soft solution processing, the so-called polymeric precursor method. In soft chemistry method, soluble precursors such as lead acetate trihydrate, calcium carbonate and titanium isopropoxide, as starting materials, were mixed in aqueous solution. Pb0.7Ca0.3TiO3 thin films were deposited on platinum-coated silicon and quartz substrates by means of the spinning technique. The surface morphology and crystal structure, dielectric and optical properties of the thin films were investigated. The electrical measurements were conducted on metal-ferroelectric-metal (MFM) capacitors. The typical measured small signal dielectric constant and dissipation factor at a frequency of 100 kHz were 299 and 0.065, respectively, for a thin film with 230 nm thickness annealed at 600degreesC for 2 h. The remanent polarization (2P(r)) and coercive field (E-c) were 32 muC/cm(2) and 100 kV/cm, respectively. Transmission spectra were recorded and from them, refractive index, extinction coefficient, and band gap energy were calculated. Thin films exhibited good optical transmissivity, and had optical direct transitions. The present study confirms the validity of the DiDomenico model for the interband transition, with a single electronic oscillator at 6.858 eV. The optical dispersion behavior of PCT thin film was found to fit well the Sellmeir dispersion equation. The band gap energy of the thin film, annealed at 600degreesC, was 3.56 eV. The results confirmed that soft solution processing provides an inexpensive and environmentally friendly route for the preparation of PCT thin films.

Photoexpansion and photorefraction in oxysulphide glasses

Oxysulphide glasses have been prepared in the pseudo binary system GeS(2.6)-Ga(2)O(3). The effect of addition of gallium oxide has been evaluated in term of thermal and optical properties. Structural behavior has been studied using Raman spectroscopy. Samples have been exposed above band gap energy (3.52 eV) varying power density and exposure time. Giant photoexpansion and photorefraction is obtained for samples containing 20% of Ga(2)O(3). (C) 2009 Elsevier B.V. All rights reserved.

A new processing method of CaZn2(OH)(6)center dot 2H(2)O powders: Photoluminescence and growth mechanism

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Cluster Coordination and Photoluminescence Properties of alpha-Ag2WO4 Microcrystals

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Structure and optical properties of [Ba1-xY2x/3](Zr0.25Ti0.75)O-3 powders

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Synthesis and photoluminescence behavior of Bi4Ti3O12 powders obtained by the complex polymerization method

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Photoluminescent behavior of BaWO4 powders processed in microwave-hydrothermal

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

(Sr,Tm)ZrO3 powders prepared by the polymeric precursor method: Synthesis, optical properties and morphological characteristics

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)