Síntese e caracterização do BaAl2O4 puro e dopado com Ce e Mn via sol-gel modificado com PVA

• Ano de defesa: 2018
• Autor(a) principal: Melo, Simone Santos
• Orientador(a): Valerio, 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: BaAl2O4; Propriedades ópticas; Aluminato de bário; Sol-gel; Síntese; Luminescência
• Área do conhecimento CNPq: CIENCIAS EXATAS E DA TERRA::FISICA
• Link de acesso: http://ri.ufs.br/jspui/handle/riufs/10742

Materials showing optical properties has been widely studied due to their wide applicability. Among them, the family formed by the calcium, strontium and barium aluminates have been studied due to the fact that some of these materials, when doped with certain ions, especially rare earth ones, are able to convert ionizing radiation to visible light. A material that can present such phenomenon is barium aluminate when doped with Cerium and/or Manganese, one of the materials that are object of study in the present work. The synthesis procedure was based on the PVA-assisted sol-gel route that shows some advantages, like methodologically simple, good homogeneity, process control phases, etc. In the first part of this work, the structural properties of barium aluminate on stoichiometry 1:2:4 (BaAl2O4) were studied upon varying the pH of the starting reactants from 1 to 4 and the synthesis temperature from 600°C to 1100°C during 5h. Samples doped with Ce or Mn and Ce and Mn were produced as well. The structural characterization of the samples was performed using Differential Thermal Analysis and Thermogravimetry (DTA/TG) techniques, showing the thermal events that occurred during the temperature variation, X-ray diffraction (XRD), allowing to find the phases present in the material and the Rietveld refinement, that was used to analyze the percentage amount of each phase in a given sample. The combined results indicated that the best condition to obtain single phase BaAlO4 is with a calcination plateau at 1100°C for 5h using the pH of the starting materials equal to 2. In the final part of this work, a study of the optical properties of the doped materials was carried out through the X-ray absorption Near Edge Structure (XANES), from where the valence of doping ions (Ce3+, 4+ and Mn2+, 3+) were analyzed, and X-Ray Excitation Optical Luminescence (XEOL) measurements in order to investigate the conversion processes that lead to the scintillation properties of these materials. Te results of the emission spectra of the samples , when excited with X-rays, presented the typical emission related to the electronic transitions of the dopant ions. The excitation spectra revealed that each one of the luminescence channels behaved differently when te excitation energy spams the energy range of the absorption edge of the matrix Ba ions or the absorption edges of the dopants. A mechanism based on the electron – hole pairs formation due to the absorption of X-rays, electron and/or hole trapping, charge recombination and energy transfer to the luminescence centres was presented.