Navegando por Palavras-chave "Optical properties"
Agora exibindo 1 - 6 de 6
Resultados por página
Opções de Ordenação
- ItemSomente MetadadadosEffect of process parameters on photophysical properties and barium molybdate phosphors characteristics(Elsevier B.V., 2014-06-01) Abreu, Maria Fernanda C. [UNIFESP]; Motta, Fabiana V.; Lima, Renata C.; Li, Maximo S.; Longo, Elson; Marques, Ana Paula de A. [UNIFESP]; Universidade Federal de São Paulo (UNIFESP); Universidade Federal de São Carlos (UFSCar); Univ Fed Rio Grande do Norte; Universidade Federal de Uberlândia (UFU); Universidade de São Paulo (USP)Barium molybdate particles (BaMoO4) with uniform shapes have applications in various fields such as phosphors, optical fibers, scintillators, magnets and catalysts. in this study, two synthesis methods (microwave-assisted hydrothermal (MAH) and Complex Polymerization (CP)) were used to prepare BaMoO4 particles. the effect of the applied synthesis methodology and experimental parameters on the morphology, particle size, sample uniformity and optical properties of the BaMoO4 were studied. Scheelite-type single crystalline structures of BaMoO4 were identified by X-ray diffraction (XRD) as well as Raman and Fourier transform infrared spectroscopy (FTIR). Octahedral morphologies were characterized by field-emission scanning electron microscopy (FE-SEM). Photoluminescence (PL) spectra of the samples exhibited different emission properties which indicates a relationship with surface defect states (shallow and deep level defects) where interfaces populate additional levels in the band gap. Electronic order-disorder at short- and intermediate-ranges is generated by utilizing the synthesis method and can be modified by applied experimental parameters. If the particle size and morphology are controlled, deep and shallow defects can be controlled, and PL properties can be modified accordingly with the optical properties desired. (C) 2014 Published by Elsevier Ltd and Techna Group S.r.l.
- ItemSomente MetadadadosEffects of microwave-assisted hydrothermal treatment and of use of capping reagent on the photophysical properties of SrMoO4 phosphors(Elsevier Science Bv, 2017) Paradelas, Sidney M. V. [UNIFESP]; Goncalves, Rosana F. [UNIFESP]; Motta, Fabiana V.; Lima, Renata C.; Li, Maximo S.; Longo, Elson; Marques, Ana Paula de A. [UNIFESP]Strontium molybdate particles (SrMoO4) with uniform shapes have applications in various fields such as phosphors, optical fibers, scintillators, magnets, sensors, and catalysts. SrMoO4 were prepared by Microwave Assisted Hydrothermal (MAH) method with variations in applied experimental parameters. The effect of the applied synthesis methodology and experimental parameters on the morphology, particle size, sample uniformity and optical properties of the SrMoO4 were studied. In this study, was observed that the microwave radiation favors an organization of material and that this organization can be changed with a capping agent, which provokes alterations in morphology, a disorder-order degree of material and variations of band gap energy. This study indicates that surface defect states favor an alteration in properties of the PL emission. The control of a surface state, the particle size and morphology can be a form to modify the property in accordance with optics characteristics the desired one.
- ItemSomente MetadadadosGrowth, structural and optical characterizations of LiLa(1-x)Eux(WO4)(2) single-crystalline fibers by the micro-pulling-down method(Elsevier B.V., 2012-03-01) Moraes, Jair Ricardo de; Baldochi, Sonia Licia; Leano Soares, Leonardo dos Reis; Mazzocchi, Vera Lucia; Ramos Parente, Carlos Benedicto; Courrol, Lilia Coronato [UNIFESP]; IPEN CNEN SP; Universidade Federal de São Paulo (UNIFESP)Transparent and uniform LiLa(1-x)Eux(WO4)(2) single-crystalline fibers where x = 0.005, 0.01, 0.03, 0.05, 0.07, 0.1, 0.15, 0.2, 0.25 and 1.0, with an average of 20-40 mm length were obtained by the micro-pulling-down method aiming structural and optical characterization. the optimum pulling rate was found to depend on the difference between alkali and rare earth ionic radii. Rietveld analysis from X-ray diffraction data and excitation spectroscopy at room temperature were applied to investigate the lattice changes due to the Eu3+ incorporation in the host. LiLa(1-x)Eux(WO4)(2) crystal fibers present red emission due to the electric dipole D-5(0) -> F-7(2) transition under 395 nm excitation showing a concentration quenching around 20 mol% of doping. the excitation spectra of the F-7(0) -> D-5(0) transition show small changes in the Eu3+ surroundings as function of dopant concentration. (C) 2011 Elsevier B.V. All rights reserved.
- ItemSomente MetadadadosInfluence of ionic liquid on the photoelectrochemical properties of ZnO particles(Elsevier Sci Ltd, 2018) Trindade, Leticia Guerreiro da; Minervino, Gabriela Bosco [UNIFESP]; Trench, Aline Barrios; Carvalho, Maria Helena; Assis, Marcelo; Li, Maximo Siu; Oliveira, Adilson Jesus Aparecido de; Pereira, Ernesto Chaves; Mazzo, Tatiana Martelli [UNIFESP]; Longo, ElsonZnO particles synthesized by the microwave-assisted hydrothermal method were sensitized with different amounts of ionic liquid (IL) 1.3-dimethylimidazolium iodide (MMI.I). The structure of the modified and unmodified ZnO particles were characterized by X-ray diffraction, Raman spectroscopy, field emission gun-scanning electron microscopy (FEG-SEM), ultraviolet-visible (UV-vis) absorption spectroscopy, photoluminescence (PL), and photoelectrochemical measurements. While the sensitization of ZnO particles by the ionic liquid does not change the ZnO phase, it reduces the particle size and converts shallow defects to deep defects. These changes cause the photocurrent density of the ZnO/IL films to increase significantly from 0.05 mA cm(-2) for pure ZnO to 0.52 and 1.24 mA cm(-2) for the ZnO films containing 20% and 35% by mass of the IL, respectively, at 1.08 V vs. Ag/AgCl. This about 24-fold increase in the photocurrent density of the ZnO/IL35 sample may indicate that the MMI.I IL may be acting as a dye, since it is constituted by an organic part, MMI+. This good performance presented by this sample indicates that this is a promising material for photoanode in solar cells.
- ItemSomente MetadadadosThe relationship between aerosol particles chemical composition and optical properties to identify the biomass burning contribution to fine particles concentration: a case study for Sao Paulo city, Brazil(Springer, 2017) de Miranda, Regina Maura; Lopes, Fabio; Rosario, Nilton Evora do [UNIFESP]; Yamasoe, Marcia Akemi; Landulfo, Eduardo; Andrade, Maria de FatimaThe air quality in the Metropolitan Area of Sao Paulo (MASP) is primarily determined by the local pollution source contribution, mainly the vehicular fleet, but there is a concern about the role of remote sources to the fine mode particles (PM2.5) concentration and composition. One of the most important remote sources of atmospheric aerosol is the biomass burning emissions from Sao Paulo state's inland and from the central and north portions of Brazil. This study presents a synergy of different measurements of atmospheric aerosol chemistry and optical properties in the MASP in order to show how they can be used as a tool to identify particles from local and remote sources. For the clear identification of the local and remote source contribution, aerosol properties measurements at surface level were combined with vertical profiles information. Over 15 days in the austral winter of 2012, particulate matter (PM) was collected using a cascade impactor and a Partisol sampler in Sao Paulo City. Mass concentrations were determined by gravimetry, black carbon concentrations by reflectance, and trace element concentrations by X-ray fluorescence. Aerosol optical properties were studied using a multifilter rotating shadowband radiometer (MFRSR), a Lidar system and satellite data. Optical properties, concentrations, size distributions, and elemental composition of atmospheric particles were strongly related and varied according to meteorological conditions. During the sampling period, PM mean mass concentrations were 17.4 +/- 10.1 and 15.3 +/- 6.9 mu g/m(3) for the fine and coarse fractions, respectively. The mean aerosol optical depths at 415 nm and Angstrom exponent (AE) over the whole period were 0.29 +/- 0.14 and 1.35 +/- 0.11, respectively. Lidar ratios reached values of 75 sr. The analyses of the impacts of an event of biomass burning smoke transport to the Sao Paulo city revealed significant changing on local aerosol concentrations and optical parameters. The identification of the source contributions, local and remote, to the fine particles in MASP can be more precisely achieved when particle size composition and distribution, vertical profile of aerosols, and air mass trajectories are analyzed in combination.
- ItemSomente MetadadadosTm3+ doped barium molybdate: A potential long-lasting blue phosphor(Elsevier Science Sa, 2018) de Azevedo Marques, Ana Paula [UNIFESP]; Kunzel, Roseli [UNIFESP]; Umisedo, Nancy K.; Latini, Renato Mazin [UNIFESP]; Yoshimura, Elizabeth Mateus; Okuno, EmicoMolybdates have applications in various fields such as phosphors, optical fibers, scintillators, magnets, sensors and catalysts. Thulium ion is an excellent blue activator and plays an important role in the design of persistent luminescent materials. This paper reports the investigation of the structural and luminescent properties of Barium Thulium Molybdate (Ba1-xTmx)MoO4 microcrystals (with x = 0, 0.01 or 0.03). The scheelite-type crystalline structure was identified from XRD and Raman studies. Under ultraviolet (359 nm) excitation, photoluminescence (PL) spectra present the characteristic emission bands at 453 nm and 545 nm which are due to the D-1(2) -> F-3(4) and D-1(2) -> H-3(4,5) transitions, respectively, from Tm3+ ions. Thermoluminescence (TL) measurements were performed with powdered samples previously irradiated with beta radiation. The depth of traps, associated with trap levels located inside the band-gap, was determined from TL data using different methods of glow curve analysis. The kinetic parameters, determined from thermoluminescent glow curves, provide evidence about a possible persistent luminescence emission from the (Ba0.97Tm0.03)MoO4 sample. This is a potential blue-light or ultraviolet long-lasting phosphor, with a trapping level lifetime, at room-temperature (300 K), of about 6 days. (C) 2017 Elsevier B.V. All rights reserved.