Influência das fases hexagonal e monoclínica do SrAl2O4 nas propriedades ópticas de nanopós dopados com Eu e Dy

• Ano de defesa: 2012
• Autor(a) principal: Santos, Claudiane dos
• Orientador(a): Valério, Mário Ernesto Giroldo
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Programa de Pós-Graduação: Pós-Graduação em Física
• Palavras-chave em Português: Físico-química; Compostos de estrôncio
• Palavras-chave em Inglês: Chemistry, Physical and theoretical
• Área do conhecimento CNPq: CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA
• Link de acesso: https://ri.ufs.br/handle/riufs/5353

Ceramic nanopowders of strontium aluminate (SrAl2O4) were produced via the Sol-Gel Proteic method. In the present work we are investigating the influence of the conditions used to produce the samples on the concentration of both phases and the influence of that on the optical properties of doped SrAl2O4 samples. When doped with rare earths (RE) ions, SrAl2O4 has attracted much attention due to its potential applications as materials that exhibit long lasting phosphorescence (LLP). The SrAl2O4 presents two crystallographic phases, a monoclinic and an hexagonal one, with a reversible phase transition at approximately 650º C, as reported by the literature. The samples were analyzed through the techniques of X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), X-Ray Excited Optical Luminescence (XEOL), radioluminenscence (RL) and X-Ray Absorption Spectroscopy (XAS). XRD analyses showed that the cooling rate has influence on the concentration of the monoclinic and hexagonal phases. The pure and Dy doped samples showed higher amount of monoclinic phase when produced with cooling rate of 10º C/min, while for the Eu doped samples, the cooling rate of 2º C/min induced the stabilization of higher amounts of monoclinic phase. This resulted can be interpreted in terms of the energetic cost involved in stabilization of the two crystalline phases including also the energetic cost of defects created by the dopants. The luminescent properties are influenced by the monoclinic to hexagonal phases concentration ratios in the samples. It was found that the dependence of the radioluminescent intensity on the concentration of the crystalline phases is defined by the specific properties of defects induced by the dopants and their environment in each crystalline phase. RL combined with XEOL and luminescence decay time excited by X-ray pulses showed that the Dy ion participates actively in the luminescent process and this is an important factor in the LLP mechanism of SrAl2O4