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.

beta-ZnMoO4 microcrystals synthesized by the surfactant-assisted hydrothermal method: Growth process and photoluminescence properties

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)

The Role of the Eu3+ Concentration on the SrMoO4:Eu Phosphor Properties: Synthesis, Characterization and Photophysical Studies

SrMoO4 doped with rare earth are still scarce nowadays and have attracted great attention due to their applications as scintillating materials in electro-optical like solid-state lasers and optical fibers, for instance. In this work Sr1-xEuxMoO4 powders, where x = 0.01; 0.03 and 0.05, were synthesized by Complex Polymerization (CP) Method. The structural and optical properties of the SrMoO4:Eu3+ were analyzed by powder X-ray diffraction patterns, Fourier Transform Infra-Red (FTIR), Raman Spectroscopy, and through Photoluminescent Measurements (PL). Only a crystalline scheelite-type phase was obtained when the powders were heat-treated at 800 A degrees C for 2 h, 2 theta = 27.8A degrees (100% peak). The excitation spectra of the SrMoO4:Eu3+ (lambda(Em.) = 614 nm) presented the characteristic band of the Eu3 + 5L6 transition at 394 nm and a broad band at around 288 nm ascribed to the charge-transfer from the O (2p) state to the Mo (4d) one in the SrMoO4 matrix. The emission spectra of the SrMoO4:Eu3+ powders (lambda(Exc.) = 394 and 288 nm) show the group of sharp emission bands among 523-554 nm and 578-699 nm, assigned to the D-5(1)-> F-7(0,1and 2) and D-5(0)-> F-7(0,1,2,3 and 4), respectively. The band related to the D-5(0)-> F-7(0) transition indicates the presence of Eu3+ site without inversion center. This hypothesis is strengthened by the fact that the band referent to the D-5(0)-> F-7(2) transition is the most intense in the emission spectra.

Crystallographic, dielectric and optical properties of SrBi2Ta2O9 thin films prepared by the polymeric precursor method

Strontium bismuth tantalate thin films were prepared on several substrates (platinized silicon (PvTi/SiO2/Si), n-type (100)-oriented and p-type (111)-oriented silicon wafers, and fused silica) by the solution deposition method. The resin was obtained by the polymeric precursor method, based on the Pechini process, using strontium carbonate, bismuth oxide, and tantalum ethoxide as starting reagents. Characterizations by XRD and SEM were performed for structural and microstructural evaluations. The electrical measurements, carried on the MFM configuration, showed P-r values of 6.24 muC/cm(2) and 31.5 kV/cm for the film annealed at 800 degreesC. The film deposited onto fused silica and treated at 700 degreesC presented around 80 % of transmittance.

Study of the annealing temperature effect on the structural and luminescent properties of SrWO4:Eu phosphors prepared by a non-hydrolytic sol-gel process

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

High-efficient microwave synthesis and characterisation of SrSnO3

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Influence of synthesis conditions on carbonate entrapment in perovskite SrSnO(3)

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Influence of Cu(II) in the SrSnO3 crystallization

Perovskite type oxides have been intensively studied due to their interesting optical, electrical, and catalytic properties. Among perovskites the alkaline earth stannates stand out, being strontium stannates (SrSnO3) the most important material in ceramic technology among them due to their wide application as dielectric component. SrSnO3 has also been applied as stable capacitor and humidity sensor. In the present work, SrSnO3:Cu was synthesized by polymeric precursor method and heat treated at 700, 800, and 900 A degrees C for 4 h. After that, the material was characterized by thermal analysis (TG/DTA), X-ray diffraction (XRD), infrared spectroscopy, and UV-vis spectroscopy. Results indicated three thermal decomposition steps and confirmed the presence of strontium carbonate and Cu2+ reduction to Cu+ at higher dopant amounts. XRD patterns indicated that the perovskite crystallization started at 700 A degrees C with strontiatite (SrCO3) and cassiterite (SnO2) as intermediate phases, disappearing at higher temperatures. The amount of secondary phase was reduced with the increase in the Cu concentration.

BaMoO4:Tb3+ phosphor properties: Synthesis, characterization and photophysical studies

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Europium(III) Concentration Effect on the Spectroscopic and Photoluminescent Properties of BaMoO4:Eu

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

Aerosol Deposition of Ba0.8Sr0.2TiO3 Thin Films

In this work we optimized conditions for aerosol deposition of homogeneous, nano-grained, smooth Ba0.8Sr0.2TiO3 thin films. Investigation involved optimization of deposition parameters, namely deposition time and temperature for different substrates. Solutions were prepared from titanium isopropoxide, strontium acetate and barium acetate. Films were deposited on Si (1 0 0) or Si covered by platinum (Pt (1 1 1) /Ti/SiO2/Si). Investigation showed that the best films were obtained at substrate temperature of 85 degrees C. After deposition films were slowly heated up to 650 degrees C, annealed for 30 min, and slowly cooled. Grain size of BST films deposited on Si substrate were in the range 40-70 nm, depending on deposition conditions, while the same films deposited on Pt substrates showed mean grain size in the range 35-50 nm. Films deposited under optimal conditions were very homogeneous, crack-free, and smooth with rms roughness lower than 4 nm for both substrates.

Tipologia de zircao e razao inicial Sr87/86Sr em series granitoides

Sr87/86Sr initial ratio data based on the isochrons from 22 granitoid complexes of Brasiliano age (Late Precambrian) from S and E Brazil are presented. The complexes have been classified into different rock series with the aid of zircon typology. A correlation between the initial ratio and the zircon typology can be determined. Of particular interest is the systematic decrease of the Sr87/86Sr initial ratio in the range from the low, through medium to the high temperature calc-alkaline series which could indicate a gradual increasing of mantle material in the genesis of calc-alkaline granitoid of progressive greater depths. -from English summary

Microstructure and phase evolution of SrTiO3 thin films on Si prepared by the use of polymeric precursors

The use of polymeric precursors was employed in preparing SrTiO3 thin films by dip coating using Si (111) as substrate. Crack free films were obtained after sintering at temperatures ranging from 550 to 1000°C. The microstructure, characterized by SEM, shows the development of dense polycrystalline films with smooth surface and mean grain size of 52 nm, for films sintered at 1000°C. Grazing incident angle XRD characterization of these films shows that the SrTiO3 phase crystallizes from an inorganic amorphous matrix. No intermediate crystalline phase was identified.

Preparation and characterization of SrBi2Nb2O9 thin films made by polymeric precursors

A polymeric precursor solution was employed in preparing SrBi2Nb2O9 (SBN) powder and thin films dip coated onto Si(100) substrate. XRD results show that the SBN perovskite phase forms at temperatures as low as 600°C through an intermediate fluorite phase. This fluorite phase is observed for samples heat-treated at temperatures of 400 and 500°C. After heat treatment at temperatures ranging from 300 to 800°C, thin films were shown to be crack free. Grazing incident angle XRD characterization shows the occurrence of the fluorite intermediate phase for films also. The thickness of films, measured by MEV, was in the order of 80-100 nm.