Structural refinement and photoluminescence properties of cube-like (Ca 1-xCu x)TiO 3 crystals synthesized by the microwave-hydrothermal method

In this work, (Ca 1-xCu x)TiO 3 crystals with (x = 0, 0.01 and 0.02), labeled as CTO, CCTO1 and CCTO2, were synthesized by the microwave-hydrothermal method at 140°C for 32 min. XRD patterns (Fig. 1), Rietveld refinement and FT-Raman spectroscopy indicated that these crystals present orthorhombic structure Pbnm. Micro-Raman and XANES spectra suggested that the substitution of Ca by Cu in A-site promoted a displacement of the [TiO6]-[TiO6] clusters adjacent from its symmetric center, which leads distortions on the [CaO 12] clusters neighboring and consequently cause the strains into the CaTiO3 lattice. FE-SEM images showed that these crystals have an irregular shape as cube like probably indicating an Ostwald-ripening and self-assemble as dominant mechanisms to crystals growth. The powders presented an intense PL blue-emission.

Structural refinement, growth mechanism, infrared/Raman spectroscopies and photoluminescence properties of PbMoO4 crystals

Lead molybdate (PbMoO4) crystals were synthesized by the co-precipitation method at room temperature and then processed in a conventional hydrothermal (CH) system at low temperature (70 °C for different times). These crystals were structurally characterized by X-ray diffraction (XRD), Rietveld refinement, micro-Raman (MR) and Fourier transformed infrared (FT-IR) spectroscopies. Field emission scanning electron microscopy images were employed to observe the shape and monitor the crystal growth process. The optical properties were investigated by ultraviolet-visible (UV-Vis) absorption and photoluminescence (PL) measurements. XRD patterns and MR spectra indicate that these crystals have a scheelite-type tetragonal structure. Rietveld refinement data possibilities the evaluation of distortions in the tetrahedral [MoO 4] clusters. MR and FT-IR spectra exhibited a high mode ν1(Ag) ascribed to symmetric stretching vibrations as well as a large absorption band with two modes ν3(Eu and Au) related to anti-symmetric stretching vibrations in [MoO 4] clusters. Growth mechanisms were proposed to explain the stages involved for the formation of octahedron-like PbMoO4 crystals. UV-Vis absorption spectra indicate a reduction in optical band gap with an increase in the CH processing time. PL properties of PbMoO4 crystals have been elucidated using a model based on distortions of tetrahedral [MoO4] clusters due to medium-range intrinsic defects and intermediary energy levels (deep and shallow holes) within the band gap. © 2012 Elsevier Ltd. All rights reserved.

The effects of water molecules on the electronic and structural properties of peptide nanotubes

The self-assembly of short amino acid chains appears to be one of the most promising strategies for the fabrication of nanostructures. Their solubility in water and the possibility of chemical modification by targeting the amino or carboxyl terminus give peptide-based nanostructures several advantages over carbon nanotube nanostructures. However, because these systems are synthesized in aqueous solution, a deeper understanding is needed on the effects of water especially with respect to the electronic, structural and transport properties. In this work, the electronic properties of l-diphenylalanine nanotubes (FF-NTs) have been studied using the Self-Consistent Charge Density-Functional-based Tight-Binding method augmented with dispersion interaction. The presence of water molecules in the central hydrophilic channel and their interaction with the nanostructures are addressed. We demonstrate that the presence of water leads to significant changes in the electronic properties of these systems decreasing the band gap which can lead to an increase in the hopping probability and the conductivity. © the Owner Societies 2013.

Synthesis, structural characterization and photophysical properties of highly photoluminescent crystals of Eu(III), Tb(III) and Dy(III) with 2,5-thiophenedicarboxylate

Lanthanide compounds of general formula [Ln2(2,5-tdc) 3(dmf)2(H2O)2] ·2dmf·H2O (Ln = Eu(III) (1), Tb(III) (2), Gd(III) (3) and Dy(III) (4), dmf = N,N′-dimethylformamide and 2,5-tdc2- = 2,5-thiophedicarboxylate anion) were synthesized and characterized by elemental analysis, X-ray powder diffraction patterns, thermogravimetric analysis and infrared spectroscopy. Phosphorescence data of Gd(III) complex showed that the triplet states (T1) of 2,5-tdc2- ligand have higher energy than the main emitting states of Eu(III), Tb(III) and Dy(III), indicating that 2,5-tdc2- ligand can act as intramolecular energy donor for these metal ions. An energy level diagram was used to establish the most relevant channels involved in the ligand-to-metal energy transfer. The high value of experimental intensity parameter Ω2 for the Eu(III) complex indicate that the europium ion is in a highly polarizable chemical environment. The emission quantum efficiency (η) of the 5D0 emitting level of Eu(III) was also determined. The complexes act as possible light conversion molecular devices (LCMDs). © 2013 Elsevier B.V. All rights reserved.

Flavonoids from the leaves of Deguelia utilis (Leguminosae): structural elucidation and neuroprotective properties

Das folhas de Deguelia utilis foram isolados cinco flavonoides: 5,3'-di-hidróxi-4'-metóxi2'',2''-dimetilcromeno-(5'',6'':6,7)-di-hidroflavonol (1), 5,3'-di-hidróxi-7,4'-dimetóxi-6,8dimetilalil-di-hidroflavonol (2), 5,3'-di-hidróxi-4'-metóxi-8-prenil-2'',2''-dimetilcromeno(5'',6'':6,7)-flavanona (3), 5,3'-di-hidróxi-7,4'-dimetóxi-6,8-dimetilalil-flavanona (4), 3,5,3'-tri-hidróxi-7,4'-dimetóxi-6,8-dimetilalil-flavanol (5), juntamente com os estilbenos: 4-metoxilonchocarpeno (6) e lonchocarpeno (7). Suas estruturas químicas foram elucidadas com base nos seus dados de NMR (ressonância magnética nuclear) e HRESITOF-MS (espectrometria de massas de alta resolução por tempo de vôo, com ionização por eletrospray). Além disso, a fim de investigar o potencial efeito citoprotetor desses flavonoides, foi utilizada uma fração eluída com hexano:AcOEt contendo os sete flavonoides, em um modelo in vitro de neurodegeneração, utilizando culturas primárias do hipocampo de ratos neonatal (PND2-P3) expostos à rotenona, um inibidor mitocondrial do complexo I. Houve uma redução significativa da viabilidade celular (19,4 ± 1,6%), quando as culturas foram expostas à rotenona 30 nmol L^-1 por 72 h. A exposição concomitante das culturas a FR3 (5 µg mL^-1) e rotenona 30 nmol L^-1 resultou em valores de viabilidade celular semelhante ao grupo controle (99,6 ± 4,8%), sugerindo um efeito citoprotetor para essa fração.

Structural refinement, optical and ferroelectric properties of microcrystalline Ba(Zr0.05Ti0.95)O-3 perovskite

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Structural, electronic and optical properties of Fe(III) complex with pyridine-2,6-dicarboxylic acid: A combined experimental and theoretical study

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

Investigation of the structural, optical and dielectric properties of highly (100)-oriented (Pb0.60Ca0.20Sr0.20)TiO3 thin films on LaNiO3 bottom electrode

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

Electrical and Superconducting Properties in Lap Joints for YBCO Tapes

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Structural, ferroelectric, and optical properties of Pb0.60Ca0.20Sr0.20TiO3, Pb0.50Ca0.25Sr0.25TiO3 and Pb0.40Ca0.30Sr0.30TiO3 thin films prepared by the chemical solution deposition technique

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

Effect of Fe-doping on the structural, microstructural, optical, and ferroeletric properties of Pb1/2Sr1/2Ti1-xFexO3 oxide prepared by spin coating technique

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

Correlation between structural and electronic order-disorder effects and optical properties in ZnO nanocrystals

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

Influence of the preparation route on the structural, morphological and spectroscopic properties of SrTiO3 and SrTiO3:eu3+ powders

This research shows the influence of the synthesis route in the structural and morphological characteristics as well as in the luminescent properties of doped with europium and pure SrTiO3 (STO) powders prepared by microwave assisted hydrothermal synthesis, MWH, and by the polymeric precursor method, PPM. The XRD at room temperature of the STO powders nominally pure obtained by PPM at 700°C for 3 hours, as well as by the MWH at 190°C by 30 minutes present all the reflection peaks for the cubic perovskite structure (JCPDS-ICDD 35-734). The morphology varies according to the synthesis route. The particles of pure STO obtained by PPM presents morphology in the form of plates and the morphology of the particles synthesized by MWH is spherical with approximately 150 nm. The photoluminescent analysis shows for pure STO wide bands associated with the transition of charge transfer from the titanates group (TiO3)2- that are centered on 450 nm. In both preparation methods the emission bands obtained in the composites spectra were found to be asymmetric and low intense. However, in the case of the STO prepared by the PPM a bigger FWHM of the band can be observed. The excitation of the samples was done using a laser (Coherent Innova) with wavelength of 350 nm.

A relationship between structural and electronic order-disorder effects and optical properties in crystalline TiO2 nanomaterials

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

Synthesis, structural characterization, luminescent properties and theoretical study of three novel lanthanide metal-organic frameworks of Ho(III), Gd(III) and Eu(III) with 2,5-thiophenedicarboxylate anion

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)