Propriedades fotoluminescentes e higroscopia do composto SrAl2O4 dopado com íons de Ni2+

• Autor(a) principal: Silveira Junior, Raimundo Nonato da
• Data de Publicação: 2015
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UERJ
• Texto Completo: http://www.bdtd.uerj.br/handle/1/12852
• topic: Optical spectroscopy; Optical properties; Photoluminescence; Crystal field; Espectroscopia óptica; Propriedades ópticas; Fotoluminescência. Campo cristalino; CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA::FISICA DA MATERIA CONDENSADA

Samples were prepared by the conventional solid-state reaction using high purity SrCO3, Al2O3 and NiO as starting reagents in stoichiometric amounts. X-ray diffraction measurements showed that only one phase is present in the samples: SrAl2O4. In this work, qualitative analysis is also obtained from scanning eletronic microscopy (SEM) images of SrAl2O4 samples doped with 0.1%, 0.5%, 1.0%, 2.0%, 5.0% and 10.0% of Ni2+ ions. Emission and excitation spectra were obtained for SrAl2O4 samples doped with 1.0% of Ni2+ ions while photoacoustic spectroscopy were performed in the samples doped with 1.0%, 2.0%, 5.0% and 10.0% of divalent nickel ions. These measurements were performed at room temperature and the aim was to investigate the electronic transitions of divalent nickel ions which entered substitutionally in the Sr2+ sites of the SrAl2O4 compound. The optical results showed the existence of three emission centers of Ni2+ ions. According to the literature, the structure of SrAl2O4 is composed of two distinct octahedral sites of Sr2+ ions, namely Sr12+ and Sr22+, whose average distances Sr1 O and Sr2 - O are, respectively, 2,800 Ǻ and 2,744 Ǻ. Since the Ni2+ ions tend to replace the Sr2+ ions, due to the fact that they have the same valence, it is considered that a part of the Ni2+ ions occupy the sites of Al3+ ions in the SrAl2O4 structure in order to justify the existence of a third emitting center of Ni2+ ions in the compound. A new octahedral site for Ni2+ ions was estimated from the edge of the tetrahedral site occupied by Al3+ ions in the SrAl2O4 compound network (considering the ionic radius of Ni2+as approximately 40% larger than the ionic radius of Al3+). The electronic transitions in the excitation and photoacoustic absorption spectra have allowed to determine the crystal field parameters (Dq) and Racah (B and C) for the three different sites occupied by Ni2+ ions in SrAl2O4. In this case, the results showed that site II occupied by Ni2+ ions is associated with Sr1 position and has a lower Dq parameter than Dq parameter associated with Ni2+ ions which have replaced the strontium ion at the site I, associated with the Sr2 position. Finally, site III has the lowest crystal field parameter Dq, then the largest ion-ligand distance is identified as the site related to the local octahedral rearrangement of the old positions of Al3+ ions. The hygroscopic features of SrAl2O4:Ni2+ are observed from the photoacoustic absorption spectra and the stretching vibrational modes of the Ni - OH and OH bonds are identified in the spectra.