Navegando por Palavras-chave "Terras raras"

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    Desenvolvimento de fósforos cerâmicos nanoestruturados puros e dopados com terras raras
    (Universidade Federal de São Paulo, 2017-12-07) Tavares, Fabio dos Santos [UNIFESP]; Marques, Ana Paula de Azevedo [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    Molybdates, with the general formula AMoO4 (A = Ca, Sr, Ba) and crystalline structure scheelite, have optical properties that make them potential candidates for use in optical devices. In the present work, calcium molybdate (CaMoO4) was doped with three rare earth ions: cerium, terbium and europium. Five types of doped materials were synthesized via Complex Polymerization Method (MPC) in addition to CaMoO4, which were divided into: three types of molybdates doped with 1% TR in relation to the Ca2+ ion Ca0,99Eu0,01MoO4, Ca0,99Tb0,01MoO4 and Ca0,99Ce0,01MoO4: Ca 0.99Eu 0.01MoO 4, CaO, 99Tb0.01MoO4 and Ca0.99Ce0.01MoO4, and two types of calcium molybdates co-doped with Ce, Tb, Eu: Ca0,97Eu0,01Tb0,01Ce0,01MoO4 and Ca0,991Eu0,0033Tb0,0033Ce0,0033MoO4. The ceramic powders obtained were characterized by XRD, Raman, MEV, Photoluminescence, FTIR, Diffuse Reflectance and XPS. With the variation of the thermal treatment temperature (400-900 ° C), we observed the modification of the properties of the doped materials when compared to the CaMoO4. Among them, there was an increase in the organization of materials with increasing temperature. With a better organization of the materials, we obtained more homogeneous and rounded grains and an amplification of the luminescent properties, obtaining emissions in the green-yellow region, of the red and low emission in the blue. The co-doped molybdates presented variations in the color of the resulting emission dependent on the heat treatment temperature applied, ranging from orange to red. X-ray diffraction allowed us to identify the Scheelite structure in pure and doped molybdates. The lanthanide ions effectively replaced the modifier ion of the network (Ca2+). Through the characterization, we observed short and long range order in the studied materials. Typical modes of asymmetric stretch and stretch stretching were detected through FTIR. Diffuse reflectance spectroscopy was used mainly for the band gap calculation. The results of this work indicate that the photoluminescent emission characteristics of the doped and co-doped calcium molybdates are of interest for application in optical devices.
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    Estudo de compósitos formados a partir de nanopartículas de fluoreto de lantânio
    (Universidade Federal de São Paulo, 2015-10-16) Secco, Henrique de Lima [UNIFESP]; Philadelphi, Laura Oliveira Peres [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    The combination of materials to form hybrids with unique properties, different from those of the isolated components, is a strategy used to prepare functional materials with improved properties aiming to allow their application in specific fields. Lanthanum fluoride is one of the rare earth ionic compounds most extensively studied nowadays, mainly due to its high ionic conductivity, which makes it attractive for sensors applications, also due to the easy doping of its structure with other rare earth elements, because of the similarity between those elements. This strategy is commonly used to obtain luminescent particles, which may be useful to the manufacturing of electronic devices? displays and biological markers, for instance. In this work, nanoparticles of lanthanum fluoride, undoped and doped with cerium and europium, were synthesized through the co-precipitation method in aqueous solution. The dynamic light scattering analyses and the zeta potential showed that the dispersions present sizes within the nanoscale and good stability. The doping by substitution of the lanthanum by other rare earth elements resulted in smaller particle sizes; and that fact is in accordance with the smaller crystallite sizes calculated for the doped samples. Aiming the formation of solid state films, composites of nanoparticles in an elastomeric matrix, the nitrile rubber (NBR), were prepared. Luminescent films were prepared through the casting and spin coating techniques, based on LaF3 doped with europium and cerium, the films presented characteristic emissions in the violet (392 nm) and orange (592 nm) regions, respectively. The thermal analysis of the composites did not show a significant gain of stability when compared to the nitrile rubber alone. The scanning electron microscopy results indicate different sizes and dispersion of the nanoparticles in the polymeric matrix for each technique of film formation; these differences may result in different optical properties of the composites.
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    Síntese e propriedades de nanocompósitos luminescentes de terras raras e SBA-15
    (Universidade Federal de São Paulo, 2017-08-17) Takamori, Dante Yugo [UNIFESP]; Martins, Tereza da Silva [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    Currently the elements known as rare earths are the object of much research due to their unique properties, amongst them, the possibility of producing luminescent materials. However, the direct excitation of rare earths is inefficient due to its low molar absortivity, making it necessary to employ other species, called matrixes, which have the purpose of absorbing electromagnetic radiation and transfering energy to luminescent ions, forming nanocrystals. A virtually unexplored method for controlling the properties of this kind of material is the use of ionic liquids (IL), which modify the reaction medium and influence the particle size, morphology and crystalline phase, consequently altering the luminescent properties. Nanocomposites that combine those luminescent materials and mesoporous silica are of great interest as they provide better stability and resistence besides having the ability of adsorbing other species. This work aimed to prepare and characterize nanocomposites made from SBA-type ordered mesoporous silica and nanocrystals (sodium yttrium fluoride (NaYF4) and yttrium oxide (Y2O3)) doped with erbium and europium rare earths, using for the latter the IL 1-butyl-3-methylimidazolium bromide (BMIBr), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF4), 1-dodecyl-3-methylimidazolium bromide (DMIBr) and 1-dodecyl-3-methylimidazolium tetrafluoroborate (DMIBF4) in the reactium medium. The influence of the IL’s cations and anions on the properties of the material was studied, as well as the regular fluorescence phenomena (downshifting) in materials with europium and the upconversion phenomena in erbium doped samples preared with different matrixes, incorporated or not into SBA-15 (nanocrystal/nanocomposite mass proportion 0.2). It was possible to obtain luminescent materials for both matrixes, both with erbium and europium, even when incorporated into silica. Distinct morphologies were obtained for Y2O3 prepared with different IL, also resulting in different quantum yield for each morphology, although displaying the same cubic crystalline phase. For the composite prepared with BMIBr, the quantum yield was comparable to the unincorporated material. Obtaining a nanocomposite as luminescent as the pure crystal is interesting for its applicability, for its properties, stability and the possibility of its functionalization with drugs, allowing to track or photoactivate them in vivo using infrared excitation luminescence, as for the erbium doped material.