Navegando por Autor "Longo, Elson"
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Artigo BaMoO4:Tb3+ phosphor properties: synthesis, characterization and photophysical studies(Elsevier, 2011) Marques, Ana Paula de Azevedo; Motta, Fabiana Villela da; Cruz, Mariana A.; Varela, José A.; Longo, Elson; Rosa, Ieda Lúcia VianaBaMoO4:Tb3+ powders were synthesized by the complex polymerization (CP) method and characterized by powder X-ray diffraction patterns (XRD), Fourier transform infra-Red (FTIR) and Raman spectroscopy as well as photoluminescence (PL) measurements. The results confirmed the presence of a crystalline scheelite-type phase in BaMoO4:Tb3+crystalline powers. Excitation spectra, λem. = 543 nm revealed the predominance of a broad band of charge transfer that was ascribed to the absorption of [MoO4]2- ionic tetragonal clusters. Emission spectra of BaMoO4:Tb3+ samples (λex. = 294 nm) have a group of sharp emission bands (456–487 nm; 543–546 nm; 581–589 nm and 617–620 nm) assigned to the 5D4 → 7 F6, 5D4 → 7 F5, 5D4 → 7 F4 and 5D4 → 7 F3 transitions of Tb3+ ions, respectively. The samples show the exponential decay curves of 5D4 → 7 F5 transition, λexc. = 294 nm and λem. = 543 nm, where the greater decay time was evaluated as 1.07 ms for the BaMoO4:Tb3+ annealed at 900 °CArtigo Effect of process parameters on photophysical properties and barium molybdate phosphors characteristics(Elsevier, 2014) Abreu, Maria Fernanda C.; Motta, Fabiana Villela da; Lima, Renata Cibely Freire de; Li, Maximo S.; Longo, Elson; Marques, Ana Paula de A.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 desiredArtigo Effects of microwave-assisted hydrothermal treatment and of use of capping reagent on the photophysical properties of SrMoO4 phosphors(Springer, 2017-12) Paradelas, Sidney M.V.; Gonçalves, Rosana F.; Motta, Fabiana Villela da; Lima, Renata Cibely Freire de; Li, Maximo S.; Longo, Elson; Marques, Ana Paula de A.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.Artigo Emissão luminescente no titanato de cálcio dopado com íons de terras-raras(Cerâmica, 2014-03) Pereira, S. C.; Paranhos, M. M.; Eduardo, Ariadne Canedo; Santos, M. A. B.; Li, Máximo Siu; Longo, Elson; Motta, Fabiana Vilella da; Figueiredo, Alberth Teixeira deAtravés do método dos precursores poliméricos foram sintetizadas amostras de Ca0,98Sr0,01X0,01TiO3 (X= Eu3+, Sm3+ ou Pr3+), que submetidas a diferentes tratamentos térmicos foram obtidas com níveis de ordem-desordem estrutural distintos. Os materiais sintetizados foram caracterizados por difração de raios X, confirmando a obtenção de um material homogêneo com estrutura perovsquita do tipo ortorrômbica. Essa caracterização permitiu ainda calcular o tamanho médio de cristalito das amostras, que varia em função do íon terra-rara presente. Os resultados da emissão fotoluminescente confirmaram a presença desse fenômeno óptico à temperatura ambiente e sua relação com o nível de ordem-desordem estrutural do sistema. A emissão fotoluminescente mais intensa ocorre nas amostras tratadas termicamente a 500 °C (independente do íon dopante), a variação do dopante influencia na intensidade da emissão devido à transferência de carga entre a matriz hospedeira e o íon terra-rara emissor, onde a amostra dopada com íon Pr3+ apresenta transferência de carga mais eficiente e consequentemente maior intensidade na emissão fotoluminescente. Outro fator que favorece a propriedade óptica das amostras é a compensação de carga, pois contribui para o aumento da desordem estrutural devido à formação de vacâncias do íon Ca2+.