Estudo do cristal CaSO4 dopado com Eu3+ por campo cristalino e por simulação de defeitos

• Ano de defesa: 2019
• Autor(a) principal: Otsuka, André Massao
• Orientador(a): Santos, Marcos Antonio Couto dos
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Programa de Pós-Graduação: Pós-Graduação em Física
• Palavras-chave em Português: CaSO4 : Eu3+; Európio; Sulfato de cálcio; Modelo de recobrimento simples; Método dos primeiros vizinhos equivalentes; Batista-Longo Improved Model (BLIM); GULP (Software)
• Palavras-chave em Inglês: Simple overlap model; Method of equivalent nearest neighbours
• Área do conhecimento CNPq: CIENCIAS EXATAS E DA TERRA::FISICA
• Link de acesso: http://ri.ufs.br/jspui/handle/riufs/11270

This work presents a theoretical study on the e ect of the crystal eld on the trivalent europium ion doping the calcium sulfate. Studies on CaSO4 : Eu3+ are largely done due to its use in thermoluminescent dosimeters because of its high sensitivity and simple preparation methods. Its spectroscopic properties allow the structural analysis of the local luminescent site and the energy levels that participate of the radiative transitions. From the experimental point of view, four possibilities of local sites have been identi ed in related literature. From the simulation point of view, the ve possible sites investigated here were obtained using the GULP software. Our new set of potentials seems to be more appropriate than those published elsewhere to simulate the dopiness of the Eu3+. The model of ionic polarization instead of the rigid-ion approximation was considered. The determination of sites followed post-analysis of defect formation energy. The Simple Overlap Model (SOM) was used together with the Method of Equivalent Nearest Neighbours (MENN) for the predictions of the Stark levels through the crystal eld parameters. The value of the charge of the central ion gEu is predicted by the Batista-Long Improved Model (BLIM) and proved to be greater than the europium ion valence. Our calculations indicated that the Eu3+ replaces sites of Ca2+ with Ca2+ vacancies as charge compensators, and there is also the possibility of formation of interstitial oxygen. In addition, after uorescence measurements to verify the 5D0 7F0 transition, the number of lines exhibited in the emission spectrum has led to the suggestion that the Eu ion occupies a distorted local symmetry which can be a combination of D2 and C2v point groups.