Navegando por Palavras-chave "Optical-Properties"

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    CaTiO3 and Ca1-3xSmxTiO3: Photoluminescence and morphology as a result of Hydrothermal Microwave Methodology
    (Elsevier Sci Ltd, 2016) Pinatti, Ivo Mateus; Mazzo, Tatiana Martelli [UNIFESP]; Goncalves, Rosana de Fatima [UNIFESP]; Varela, Jose Arana; Longo, Elson; Rosa, Ieda Lucia Viana
    Calcium titanate (CaTiO3 - CT) and samarium doped calcium titanate (CaTiO3:Sm3+ - CT:Sm) powders in different Sm3+ concentrations (0.5-5.0% molar ratio of Sm3+) were obtained by the Hydrothermal Microwave Methodology at 140 degrees C for 16 min. These crystals were structurally characterized by X-ray diffraction (XRD) and micro-Raman (MR) spectroscopy. Field emission scanning electron microscopy images were employed to observe the shape and size of the crystals. The optical properties were investigated by ultraviolet visible (UV Vis) absorption and photoluminescence (PL) measurements. The XRD indicated structural organization at long range while MR revealed short range order for all undoped and Sm-doped samples. Morphological analysis revealed a new cubic morphology for CT:Sm, presenting an average size of 3.0 mu m. Further, the ultraviolet visible absorption spectra indicated the existence of intermediary energy levels within the band gap. The maximum intensity PL emission occurred due to (4)G(5/2) -> H-6(7/2) and (4)G(5/2) -> H-6(9/2), transitions of Sm3+. CIE chromaticity coordinates of the samples were determined and support these materials are promising candidates for applications as phosphors in the visible orange range. This research concluded that the methodology employed here was responsible for the presence of unusual and interesting properties for these new luminescent materials. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
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    CaTiO3 and Ca1-3xSmxTiO3: Photoluminescence and morphology as a result of Hydrothermal Microwave Methodology
    (Elsevier Sci Ltd, 2016) Pinatti, Ivo Mateus; Mazzo, Tatiana Martelli [UNIFESP]; Gonçalves, Rosana de Fátima [UNIFESP]; Varela, Jose Arana; Longo, Elson; Rosa, Ieda Lucia Viana
    Calcium titanate (CaTiO3 - CT) and samarium doped calcium titanate (CaTiO3:Sm3+ - CT:Sm) powders in different Sm3+ concentrations (0.5-5.0% molar ratio of Sm3+) were obtained by the Hydrothermal Microwave Methodology at 140 degrees C for 16 min. These crystals were structurally characterized by X-ray diffraction (XRD) and micro-Raman (MR) spectroscopy. Field emission scanning electron microscopy images were employed to observe the shape and size of the crystals. The optical properties were investigated by ultraviolet visible (UV Vis) absorption and photoluminescence (PL) measurements. The XRD indicated structural organization at long range while MR revealed short range order for all undoped and Sm-doped samples. Morphological analysis revealed a new cubic morphology for CT:Sm, presenting an average size of 3.0 mu m. Further, the ultraviolet visible absorption spectra indicated the existence of intermediary energy levels within the band gap. The maximum intensity PL emission occurred due to (4)G(5/2) -> H-6(7/2) and (4)G(5/2) -> H-6(9/2), transitions of Sm3+. CIE chromaticity coordinates of the samples were determined and support these materials are promising candidates for applications as phosphors in the visible orange range. This research concluded that the methodology employed here was responsible for the presence of unusual and interesting properties for these new luminescent materials. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
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    Using femtosecond lasers to modify sizes of gold nanoparticles
    (Spie-int soc optical engineering, 2016) Cordeiro, Thiago da Silva; de Matos, Ricardo Almeida [UNIFESP]; de Oliveira Silva, Flavia Rodrigues; Vieira, Nilson Dias, Jr.; Courrol, Lilia Coronato [UNIFESP]; Samad, Ricardo Elgul
    Metallic nanoparticles are important on several scientific, medical and industrial areas. The control of nanoparticles characteristics has fundamental importance to increase the efficiency on the processes and applications in which they are employed. The metallic nanoparticles present specific surface plasmon resonances (SPR). These resonances are related with the collective oscillations of the electrons presents on the metallic nanoparticle. The SPR is determined by the potential defined by the nanoparticle size and geometry. There are several methods of producing gold nanoparticles, including the use of toxic chemical polymers. We already reported the use of natural polymers, as for example, the agar-agar, to produce metallic nanoparticles under xenon lamp irradiation. This technique is characterized as a "green" synthesis because the natural polymers are inoffensive to the environment. We report a technique to produce metallic nanoparticles and change its geometrical and dimensional characteristics using a femtosecond laser. The 1 ml initial solution was irradiate using a laser beam with 380 mW, 1 kHz and 40 nm of bandwidth centered at 800 nm. The setup uses an Acousto-optic modulator, Dazzler, to change the pulses spectral profiles by introduction of several orders of phase, resulting in different temporal energy distributions. The use of Dazzler has the objective of change the gold nanoparticles average size by the changing of temporal energy distributions of the laser pulses incident in the sample. After the laser irradiation, the gold nanoparticles average diameter were less than 15 nm.