Submitted by Ronan Geraldo Ferreira null (ronangf@hotmail.com) on 2017-10-03T15:35:46Z No. of bitstreams: 1 dissertação.pdf: 5250871 bytes, checksum: d36c87eede9dd24c78834e601f6fe208 (MD5) / Approved for entry into archive by Monique Sasaki (sayumi_sasaki@hotmail.com) on 2017-10-03T16:50:50Z (GMT) No. of bitstreams: 1 ferreira_rg_me_araiq.pdf: 5250871 bytes, checksum: d36c87eede9dd24c78834e601f6fe208 (MD5) / Made available in DSpace on 2017-10-03T16:50:50Z (GMT). No. of bitstreams: 1 ferreira_rg_me_araiq.pdf: 5250871 bytes, checksum: d36c87eede9dd24c78834e601f6fe208 (MD5) Previous issue date: 2017-09-19 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Os cintiladores são compostos que podem absorver radiações ionizantes e convertê-las eficientemente em radiações UV-VIS. Avanços na tecnologia de detecção, a busca por novos cintiladores com alta eficiência e a compreensão do mecanismo de cintilação ainda é o foco de várias pesquisas nesta área. Os compostos GdP3O9 dopados com Eu3+, Tb3+ e Sm3+ são materiais cintiladores promissores, os átomos de Terras raras na estrutura de GdP3O9 são isolados um do outro a uma grande distância (5 a 7 Å) , aumentando o concentração máxima necessária para atingir a supressão por concentração e melhores propriedades de luminescência, uma vez que eles têm alta densidade, valores elevados de coeficiente de atenuação de massa e propriedades espectroscópicas relevantes, como emissão brilhante, vida útil de mili ou microssegundos e transferência de energia eficiente de íons Gd3+ para os ativadores. Este trabalho descreve a preparação de GdP3O9 nominalmente puro e dopado com Eu3+, Tb3+ e Sm3+ pelo método de precipitação homogênea (utilizando o precursor nanoparticulado Gd(OH)CO3) e o estudo de suas propriedades estruturais e espectroscópicas (fotoluminescência e excitação por raios X ). O perfil espectral da emissão de GdP3O9 dopado com Eu3+ indica a ocupação de dois locais diferentes pelos íons dopantes, um sitio de alta simetria e um sitio de baixa simetria. A intensidade de emissão aumenta ao incorporar Eu3+ e Tb3+ no hospedeiro GdP3O9 até a concentração de 8%, enquanto que na amostra dopada com Sm3+ observa-se uma supressão por concentração em concentrações superiores a 4%. / Scintillators materials are compounds that can absorb ionizing radiations and efficiently convert them into UV-VIS radiations. Advances in the technology of detection, the search for new scintillators materials with high efficiency and for the understanding of the scintillation mechanism is still the focus of research in this area. The compounds GdP3O9 doped with Eu3+, Tb3+ and Sm3+ are promising scintillators materials, The RE atoms in GdP3O9 structure are isolated from each other for a big distance(5 to 7 Å) , which may lead to a higher quenching concentration and better luminescence properties, since they have high density, high values of mass attenuation coefficient and relevant spectroscopic properties, such as bright emission, lifetime of milli or microseconds and the efficient energy transfer from Gd3+ ions to the activators. This work describes the preparation of GdP3O9 nominally pure and doped with Eu3+, Tb3+ e Sm3+ by the homogeneous precipitation method (using the nanoparticulate precursor Gd(OH)CO3) and the study of their structural and spectroscopic (photoluminescence and X-rays excited optical luminescence) properties. Emission spectral profile of Eu3+- doped GdP3O9 indicates the occupation of two different sites by the dopant ions, a high symmetry site and a low symmetry site. The emission intensity increases by incorporating Eu3+ and Tb3+ in the GdP3O9 host until the concentration of 8 at.%, while in the Sm3+ doped sample a quenching concentration is observed at concentrations greater than 4. %.

<p>Silicon nanostructures formed in silicon-rich silicon nitride (SRSN) and cerium and terbium doped silicon oxide thin films grown using different types of plasma-enhanced chemical vapour deposition have been studied through photoluminescence (PL) and synchrotron-based X-ray absorption spectroscopies to determine the effects of deposition and processing parameters on the luminescent and structural properties of these materials. The SRSN films exhibited bright PL attributed to quantum confinement effects in the silicon nanoclusters (Si-ncs) as well as radiative defects in the silicon nitride host matrix. The peak emission energy could be tuned from the near-infrared across the entire visible spectrum by controlling the film composition and the post-deposition annealing temperature and time to change the size of the Si-ncs. Preliminary experiments on cerium doped SRSN samples indicated that although the cerium ions coordinate in the optically active trivalent oxidation state, they were not effectively sensitized by Si-ncs in the films tested, most likely due to the nanoclusters having bandgap energies that were unsuitable for this purpose. In cerium and terbium co-doped silicon oxide films, cerium disilicate (Ce₂Si₂O₇) nanocrystallites were formed by annealing at temperatures of 900°C and higher. The A-Ce₂Si₂O₇, G-Ce₂Si₂O₇, and Ce₆[Si₄O₁₃][SiO₄]₂ phases of cerium disilicate were observed to form under different deposition and annealing conditions. All three phases exhibited extremely bright violet-blue PL and were found to efficiently sensitize green emission from co-dopant Tb³⁺ ions in the films. The Tb³⁺ luminescence predominantly corresponded to the ⁵D₄→⁷F_3–6 emission lines, although weak ⁵D₃→⁷F_2–6 emission lines were also observed in films containing relatively high concentrations of terbium indicating that the sensitization of Tb³⁺ ions occurred through the ⁵D₃, ⁵L₁₀, or ⁵D₂ energy levels.</p> / Doctor of Philosophy (PhD)