Identifying and rationalizing the morphological, structural, and optical properties of β-Ag2MoO4 microcrystals, and the formation process of Ag nanoparticles on their surfaces: combining experimental data and first-principles calculations

We present a combined theoretical and experimental study on the morphological, structural, and optical properties of β-Ag2MoO4 microcrystals. β-Ag2MoO4 samples were prepared by a co-precipitation method. The nucleation and formation of Ag nanoparticles on β-Ag2MoO4 during electron beam irradiation were also analyzed as a function of electron beam dose. These events were directly monitored in real-time using in situ field emission scanning electron microscopy (FE-SEM). The thermodynamic equilibrium shape of the β-Ag2MoO4 crystals was built with low-index surfaces (001), (011), and (111) through a Wulff construction. This shape suggests that the (011) face is the dominating surface in the ideal morphology. A significant increase in the values of the surface energy for the (011) face versus those of the other surfaces was observed, which allowed us to find agreement between the experimental and theoretical morphologies. Our investigation of the different morphologies and structures of the β-Ag2MoO4 crystals provided insight into how the crystal morphology can be controlled so that the surface chemistry of β-Ag2MoO4 can be tuned for specific applications. The presence of structural disorder in the tetrahedral [MoO4] and octahedral [AgO6] clusters, the building blocks of β-Ag2MoO4, was used to explain the experimentally measured optical properties

Photoexpansion and photobleaching effects in oxysulfide thin films of the GeS2+Ga2O3 system

Oxysulfide systems undergo structural transformations upon illumination with laser light of near bandgap energy, as well as chalcogenide materials (glasses and films). In this paper, photoinduced effects such as photoexpansion and photobleaching were observed in GeS2+Ga2O3 (GGSO) films synthesized by electron beam evaporation. A surface expansion of the thin films and a shift to shorter wavelengths of the optical absorption edge were observed as a result of UV laser irradiation (wavelength of 351 nm) and they are dependent on laser power density, exposure time and film composition. These parameters were varied to evaluate and enhance the observed effects. In addition, the irradiated GGSO samples exhibited a decrease in refractive index, measured with a prism-coupling technique, which makes these films suitable candidates for applications as gratings and waveguides in integrated optics.FAPESP (05/58396-0

Effect of partial preferential orientation and distortions in octahedral clusters on the photoluminescence properties of FeWO4 nanocrystals

This communication is a report of our initial research to obtain iron tungstate (FeWO4) nanocrystals by the microwave-hydrothermal method at 170 degrees C for 45 min. X-ray diffraction patterns showed that the FeWO4 nanocrystals prepared with polyethylene glycol-200 have a partial preferential orientation in the (011) plane in relation to other nanocrystals prepared with sodium bis(2-ethylhexyl) sulfosuccinate and water. Rietveld refinement data indicates that all nanocrystals are monophasic with wolframite-type monoclinic structures and exhibit different distortions on octahedral [FeO6]/[WO6] clusters. High resolution transmission electron microcopy revealed an oriented attachment mechanism for the growth of aggregated FeWO4 nanocrystals. Finally, we observed that the photoluminescence properties of these nanocrystals are affected by partial preferential orientation in the (011) plane and distortions on [FeO6]/[WO6] clusters.Brazilian research financing institution FAPESPBrazilian research financing institution: FAPESP [2009/53189-8, 2009/50303-4]Brazilian research financing institution: CNPq [159710/2011-1]Brazilian research financing institution: CNPqBrazilian research financing institution: CAPESBrazilian research financing institution: CAPE

Microstructure, dielectric properties and optical band gap control on the photoluminescence behavior of Ba['Zr IND.0.25''Ti IND. 0.75]'O IND.3' thin films

Ba[Zr0.25Ti0.75]O3 (BZT) thin films were synthesized\ud by the complex polymerization method and heat\ud treated at 400 C for different times and at 700 C for 2 h.\ud These thin films were analyzed by X-ray diffraction\ud (XRD), Fourier-transform infrared (FT-IR) spectroscopy,\ud field emission gun-scanning electron microscopy (FEGSEM)\ud and atomic force microscopy (AFM), Ultraviolet–\ud visible (UV–vis) absorption spectroscopy, electrical and\ud photoluminescence (PL) measurements. FEG-SEM and\ud AFM micrographs showed that the microstructure and\ud thickness of BZT thin films can be influenced by the processing\ud times. Dielectric constant and dielectric loss of\ud BZT thin films heat treated at 700 C were approximately\ud 148 and 0.08 at 1 MHz, respectively. UV–vis absorption\ud spectra suggested the presence of intermediary energy\ud levels (shallow and deep holes) within the band gap of BZT\ud thin films. PL behavior was explained through the optical\ud band gap values associated to the visible light emission\ud components.CAPESCNPqFAPES

Structure and optical properties of [Ba(1-x)Y(2x/3)](Zr0.25Ti0.75)O3 powders

[Ba1–xY2x/3](Zr0.25Ti0.75)O3 powders with different yttrium concentrations (x = 0, 0.025 and 0.05) were prepared by solid state reaction. These powders were analyzed by X-ray diffraction (XRD), Fourier transform Raman scattering (FT-RS), Fourier transform infrared (FT-IR) and X-ray absorption near-edge (XANES) spectroscopies. The optical properties were investigated by means of ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL) measurements. Even with the addition of yttrium, the XRD patterns revealed that all powders crystallize in a perovskite-type cubic structure. FT-RS and FT-IR spectra indicated that the presence of [YO6] clusters is able to change the interaction forces between the O-Ti-O and O-Zr-O bonds. XANES spectra were used to obtain information on the off-center Ti displacements or distortion effects on the [TiO6] clusters. The different optical band gap values estimated from UV-vis spectra suggested the existence of intermediary energy levels (shallow or deep holes) within the band gap. The PL measurements carried out with a 350 nm wavelength at room temperature showed that all powders present typical broad band emissions in the blue region.FAPESP (09/50303-4)CNPqCAPESLNLS (D04B - XAFS1 - 8823

Intense blue and green photoluminescence emissions at room temperature in barium zirconate powders

Intense blue and green photoluminescence (PL) emissions were observed at room temperature in barium zirconate (BaZrO3) powders prepared by chemical method. The powders were analyzed by X-ray diffraction (XRD), X-ray absorption near edge spectroscopy (XANES), extended X-ray absorption spectroscopy (EXAFS) and ultraviolet–visible (UV–vis) absorption spectroscopy. The XRD patterns indicated the presence of a secondary phase of BaCO3 in BaZrO3 powders heat treated at 773 K. K-edge XANES data revealed that Zr atoms presents in at least two Zr environments. EXAFS investigations showed strong bond length dispersion in the first coordination shell around Zr atoms. EXAFS analysis indicated that Zr atoms are coordinated by 6 oxygen in BaZrO3 powders heat treated at 973 K. UV–vis measurements suggested the presence of intermediary energy levels into the band gap of BaZrO3 powders heat treated at 773 K. The intense PL emission in BaZrO3 powders can be attributed to the two Zr environments or ZrO5–ZrO6 clusters.CAPESFAPESPCNPQLaboratório Nacional de Luz Síncrotron (LNLS

Effect of different solvent ratios (water/ethylene glycol) on the growth process of CaMo'O IND.4' crystals and their optical properties

ABSTRACT: In this paper, calcium molybdate (CaMoO4) crystals (meso- and nanoscale) were synthesized by the coprecipitation\ud method using different solvent volume ratios (water/ethylene glycol). Subsequently, the obtained suspensions were\ud processed in microwave-assisted hydrothermal/solvothermal systems at 140 C for 1 h. These meso- and nanocrystals processed\ud were characterized by X-ray diffraction (XRD), Fourier transform Raman (FT-Raman), Fourier transform infrared (FT-IR),\ud ultraviolet-visible (UV-vis) absorption spectroscopies, field-emission gun scanning electron microscopy (FEG-SEM),\ud transmission electron microscopy (TEM), and photoluminescence (PL) measurements. XRD patterns and FT-Raman spectra\ud showed that these meso- and nanocrystals have a scheelite-type tetragonal structure without the presence of deleterious phases.\ud FT-IR spectra exhibited a large absorption band situated at around 827 cm-1, which is associated with the Mo-O antisymmetric\ud stretching vibrations into the [MoO4] clusters. FEG-SEM micrographs indicated that the ethylene glycol concentration\ud in the aqueous solution plays an important role in the morphological evolution of CaMoO4 crystals. High-resolution\ud TEM micrographs demonstrated that the mesocrystals consist of several aggregated nanoparticles with electron diffraction\ud patterns of monocrystal. In addition, the differences observed in the selected area electron diffraction patterns of CaMoO4\ud crystals proved the coexistence of both nano- and mesostructures. First-principles quantum mechanical calculations based on\ud the density functional theory at the B3LYP level were employed in order to understand the band structure and density of states\ud for the CaMoO4. UV-vis absorption measurements evidenced a variation in optical band gap values (from 3.42 to 3.72 eV) for\ud the distinct morphologies. The blue and green PL emissions observed in these crystals were ascribed to the intermediary energy\ud levels arising from the distortions on the [MoO4] clusters due to intrinsic defects in the lattice of anisotropic/isotropic crystals.FAPESP (09/50303-4)CNPqCAPE

Electronic structure, growth mechanism and photoluminescence of CaW'O IND. 4' crystals

In this paper, aggregated CaWO4 micro- and nanocrystals were synthesized by the co-precipitation method and processed under microwave-assisted hydrothermal/solvothermal conditions (160 °C for 30 min). According to the X-ray patterns, all crystals exhibited only the scheelite-type tetragonal structure. The data obtained by the Rietveld refinements revealed that the oxygen atoms occupy different positions in the [WO4] clusters, suggesting the presence of lattice distortions. The crystal shapes as well as its crystallographic orientations were identified by field-emission scanning electron microscopy and high-resolution transmission electron microcopy. Electronic structures of these crystals were evaluated by the first-principles quantum mechanical calculations based on the density functional theory in the B3LYP level. A good correlation was found between the experimental and theoretical Raman and infrared-active modes. A crystal growth mechanism was proposed to explain the morphological evolution. The ultraviolet-visible absorption spectra indicated the existence of intermediary energy levels within the band gap. The highest blue photoluminescence emission, lifetime and quantum yield were observed for the nanocrystals processed in the microwave-assisted solvothermal method.FAPESP (09/50303-4 09/53189-8/ 08/55585-5)CAPESCNP

Synthesis of (Ca,Nd)Ti'O IND.3' powders by complex polymerization, Rietveld refinement and optical properties

Neodymium calcium titanate, (Ca0.99Nd0.01)TiO3 powders were synthesized by the complex polymerization method and heat treated at different temperatures for 2 h under air atmosphere. The structural evolution of these powders as a function of heat treatment temperature was analyzed by X-ray diffraction (XRD) and micro-Raman (MR) spectroscopy. The optical properties were investigated by Ultraviolet–visible (UV–vis) absorption spectroscopy and Photoluminescence (PL) measurements. XRD patterns, Rietveld refinement and MR spectra indicated that the powders heated treated at 750 °°C for 2 h present an orthorhombic structure without secondary phases. UV–vis measurements suggested the presence of intermediary energy in disordered (Ca0.99Nd0.01)TiO3 powders. Broad and narrow bands were observed in the PL spectra of these powders when excited with 350 nm wavelength. The broad bands were associated to the structural defects and/or p–d electronic transitions while, the narrow bands were ascribed to f–f transitions arising from Nd3+ ions.CAPESCNPQFAPES

Retinoblastoma Loss Modulates DNA Damage Response Favoring Tumor Progression

Senescence is one of the main barriers against tumor progression. Oncogenic signals in primary cells result in oncogene-induced senescence (OIS), crucial for protection against cancer development. It has been described in premalignant lesions that OIS requires DNA damage response (DDR) activation, safeguard of the integrity of the genome. Here we demonstrate how the cellular mechanisms involved in oncogenic transformation in a model of glioma uncouple OIS and DDR. We use this tumor type as a paradigm of oncogenic transformation. In human gliomas most of the genetic alterations that have been previously identified result in abnormal activation of cell growth signaling pathways and deregulation of cell cycle, features recapitulated in our model by oncogenic Ras expression and retinoblastoma (Rb) inactivation respectively. In this scenario, the absence of pRb confers a proliferative advantage and activates DDR to a greater extent in a DNA lesion-independent fashion than cells that express only HRasV12. Moreover, Rb loss inactivates the stress kinase DDR-associated p38MAPK by specific Wip1-dependent dephosphorylation. Thus, Rb loss acts as a switch mediating the transition between premalignant lesions and cancer through DDR modulation. These findings may have important implications for the understanding the biology of gliomas and anticipate a new target, Wip1 phosphatase, for novel therapeutic strategies