Estudo estrutural e óptico do CaF2, SrF2 e LiCaAlF6 produzidos pelo método hidrotermal assistido por micro-ondas

• Autor(a) principal: Bezerra, Claudiane dos Santos
• Data de Publicação: 2016
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Repositório Institucional da UFS
• Texto Completo: https://ri.ufs.br/handle/riufs/5266
• topic: Física; Fluoreto de Cálcio; Fluoreto de estrôncio; Compostos de lítio; Método hidrotermal; Alteração hidrotermal; Microondas; CIENCIAS EXATAS E DA TERRA::FISICA

In this work, CaF2, SrF2 and LiCaAlF6 pure and doped with rare earths were produced by microwave-assisted hydrothermal synthesis, which is a promising method to produce nanostructured powders in a simple, low cost and fast way. The samples were produced with or without using chelating agent and synthesized at low temperature, under pressure and a short time period. The crystalline phases of the samples were identified by X-ray diffraction (XRD) and the morphology of the particles was determined by scanning electron microscopy (SEM). The particles present similar morphology to CaF2 and SrF2 samples produced with and without using chelating agent. While the LiCaAlF6 samples presented a different morphology when produced with EDTA. The study of the chemical composition of CaF2 was performed by X-ray Photoelectron Spectroscopy (XPS) and the results indicated the presence of reasonable amounts of hydroxyl groups and oxygen ions in the samples produced with chelating agent. Optical study was conducted by emission and excitation spectra to understand the band structure and to determine the band gap of the materials. The emission spectrum showed that the CaF2 and SrF2 presents an intrinsic luminescence with an band at approximately 300 nm associated with the exciton emission. The fundamental absorption associated to the band gap was estimated at 11.7 eV for CaF2, 10.9 eV for SrF2 and 12.1 eV for LiCaAlF6. The emission and excitation spectra were measured in the Toroidal Grating Monochromator (TGM) beamline of the Brazilian Synchrotron Light Laboratory (LNLS) and the results shown evidences that the formation energy of the exciton and band gap energy are smaller than the ones for the single crystal.