Fotocromismo e luminescência de compostos a base de tungstênio e íons terras raras trivalentes via síntese hidrotérmica

• Autor(a) principal: Sobrinho, Josiane Aparecida [UNESP]
• Data de Publicação: 2015
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional da UNESP
• Texto Completo: http://hdl.handle.net/11449/124471
• topic: Tungstenio; Luminescencia; Fotocromismo; Terras raras; Raio X; Luminescence

Systems containing rare earth elements have many applications due to their spectroscopic and magnetic properties. On the other hand tungsten-based compounds form a large class of inorganic materials which exhibit interesting physical properties, particularly photochromism. Among W6+ compounds, oxy-hydroxide containing tungsten and rare earth ions, with formula TRW2O6(OH)3, stands out with few reports in the literature. Thus, the aim of this study is to evaluate the structural and spectroscopic properties of oxy-hydroxides with tungsten and trivalent cations of rare earth elements, synthesized via hydrothermal method, by which the phase is easily obtained. The addition of citric acid to the synthesis leads to effective control of particles morphology, and even remaining as a residue in samples in which it is employed, it does not cause significant distortion of the crystal structure. Furthermore, this additive promotes the reduction of W6+ ions to the oxidation state (V), which has a great influence on the optical properties of the studied phase. The reflectance data show an intense absorption band which extends over the entire visible and near infrared spectral range, assigned to the intervalence charge transfer transitions (IVCT) between W5+ and adjacent W6+ ions. Irradiation of the material with energies exceeding the bandgap leads to an increase in the band associated with the IVCT and subsequent color change of the material, which indicates the occurrence of photochromism; when the excitation is done in the ultraviolet spectral region, the photochromic effect is enhanced by the photodecomposition of citric acid residues. The increased bandwidth associated with the IVCT leads concomitantly to the suppression of emissions from Eu3+ 5D0 emitting level, resulting in an exponential decrease of the emission intensity profile as the material is continuously irradiated. This observation suggests that...