Navegando por Palavras-chave "Rare earths"

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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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    Dosimetria ambiental de areia monazítica das praias do litoral norte de São Paulo
    (Universidade Federal de São Paulo, 2021-02-23) Teissiere, Luigi Leite [UNIFESP]; Tatumi, Sonia Hatsue [UNIFESP]; http://lattes.cnpq.br/5410340106554020; http://lattes.cnpq.br/2287413815393341; Universidade Federal de São Paulo (UNIFESP)
    Algumas praias do litoral norte de São Paulo apresentam areias monazíticas, que são areias que contêm terras raras e isótopos radioativos, deste modo, é possível afirmar que emite radiação gama. Quando o ser humano é exposto a doses de radiação, pode resultar em alguns danos celulares, podendo evoluir para um câncer. O objetivo deste trabalho é estabelecer uma análise da dose de radiação gama emitida pela areia e comparar com os limites estabelecidos pelos órgãos reguladores. Foi utilizado o Detector de Germânio Puro de Camberra e a Rigaku MiniFlex 300 para as análises de dose anual das areias colhidas e as suas estruturas cristalinas. As doses das amostras da Praia da Mococa foram as que mais se aproximaram do limite natural de 10 mSv/ano estabelecido pela CNEN. E também foram encontradas estruturas de terras raras com o método de Difração de Raios X.
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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.