Call number: LD2668 .T4 1985 A42 / Master of Science

No description available.

L' intérêt des phases oxydes à base de terres rares est certes multiple et leurs propriétésont été explorées depuis longtemps: mais nous nous intéressons ici aux comportements de cesphases en tant que phases thermiques, catalytiques ou conductrices ioniques à hautetempérature. Il s'agit en particulier de développer des systèmes innovants de matériauxpouvant intervenir dans la conception de dispositifs pour la microélectronique, pour capteursde gaz ou membranes sélectives ou pour systèmes dépolluants.Les phases de structure pyrochlore ou fluorine de type TR2Ce207 où TR désigne unélément de Terre Rare présentent divers potentiels d' applications: elles ont été considéréescomme des phases pouvant résister à de hautes températures. Les oxydes de structurespérovskites, de formule générale ABO), présentent de multiples applications potentielles,notamment en tant que phases diélectriques pour condensateurs, ou phases conductricesioniques (en ions oxygène ou en protons) pour électrolytes solides, du fait même de leur hautestabilité chimique à haute température.Ce travail a été divisé en deux parties. La première a consisté à élaborer la phase« thermique)} de type pyrochlore TR2Ce20 7 (TR = La, Ce, ... ) en utilisant un minéralcomplexe à base d'allanite-monazite et de silico-aluminates issus de déchets industriels, doncà bas coût.La deuxième partie a consisté à élaborer BaCe03 et à étudier ses propriétéscatalytiques et conductimétriques en fonction de la température. Une nouvelle méthode desynthèse reposant sur l' utilisation du mélange EDTA-citrate a été utilisée afin d'élaborer unprécurseur, qui, traité thermiquement à 950°C, a permis d'élaborer des poudressubmicroniques de la phase BaCe03. L'activité catalytique du composé BaCe03 démarre à450°C pour atteindre la conversion totale à 675°C : dans cette gamme de température,l'efficacité catalytique de la phase BaCe03 est maximale. L'évolution de la conductivité enfonction de la température de pastilles compactées de BaCe03 a révélé l'existence d'une sériede modifications électriques fortement corrélées aux transitions structurales connues pourBaCe03 dans la littérature. À basse température (300 à 450°C), la faible conductivité de laphase orthorhombique, associée à la faible énergie d'activation, peut être liée à la migrationdes défauts extrinsèques (gaz adsorbés). Cependant, au-dessus de 500°C, la conductivité de laseconde phase orthorhombique augmente: ceci pourrait être attribué à une mobilité croissantedes atomes d'oxygène. / Rare earth elements have recently been involved in a range of advanced technologies like microelectronics, membranes for catalytic conversion and applications in gas sensors. In the family of rare earth elements like cerium can play a key role in such industrial applications. However, the high cost of these materials and the control and efficiencies associated processes required for its use in advanced technologies, are a permanent obstacle to its industrial development. In present study was proposed the creation of phases based on rare earth elements that can be used because of its thermal behavior, ionic conduction and catalytic properties. This way were studied two types of structure (ABO3 and A2B2O7), the basis of rare earths, observing their transport properties of ionic and electronic, as well as their catalytic applications in the treatment of methane. For the process of obtaining the first structure, a new synthesis method based on the use of EDTA citrate mixture was used to develop a precursor, which undergone heat treatment at 950 ° C resulted in the development of submicron phase BaCeO3 powders. The catalytic activity of perovskite begins at 450 ° C to achieve complete conversion at 675 ° C, where at this temperature, the catalytic efficiency of the phase is maximum. The evolution of conductivity with temperature for the perovskite phase revealed a series of electrical changes strongly correlated with structural transitions known in the literature. Finally, we can establish a real correlation between the high catalytic activity observed around the temperature of 650 ° C and increasing the oxygen ionic conductivity. For the second structure, showed clearly that it is possible, through chemical processes optimized to separate the rare earth elements and synthesize a pyrochlore phase TR2Ce2O7 particular formula. This "extracted phase" can be obtained directly at low cost, based on complex systems made of natural minerals and tailings, such as monazite. Moreover, this method is applied to matters of "no cost", which is the case of waste, making a preparation method of phases useful for high technology applications. / Elementos terras raras têm sido recentemente envolvido em uma ampla gama de tecnologias avançadas, como a microeletrônica, membranas para a conversão catalítica e aplicações em sensores de gás. Na família de terras raras, elementos como o cério pode desempenhar um papel chave em tais aplicações industriais. No entanto, o alto custo desses materiais e do controle e eficiências dos processos associados necessários para sua utilização em tecnologias avançadas, são um obstáculo permanente ao seu desenvolvimento industrial. No presente trabalho, foi proposto a obtenção de duas fases baseadas em elementos de terras raras que podem ser utilizados devido o seu comportamento térmico, condução iônica e propriedades catalíticas. Desta maneira, foram estudados dois tipos de estrutura (ABO3 e A2B2O7), a base de terras raras, observando suas propriedades de transporte iônico e eletrônico, bem como suas aplicações catalíticas no tratamento do metano. Durante o processo de obtenção da primeira estrutura, um novo método de síntese baseado no uso da mistura EDTA citrato foi usado para desenvolver um precursor, que submetidos a tratamento térmico a 950°C, resultou no desenvolvimento de pós submicrométricos da fase BaCeO3. A atividade catalítica desta perovskita começa a 450°C para alcançar a conversão completa em 675°C, onde nesta temperatura, a eficiência catalítica da fase é máxima. A evolução da condutividade em função da temperatura para a fase perovskita revelou uma série de mudanças elétricas fortemente correlacionada com transições estruturais conhecida na literatura. Finalmente, pode-se estabelecer uma correlação real entre a alta atividade catalítica observada em torno da temperatura de 650°C e o aumento da condutividade iônica de oxigênio. Para a segunda estrutura, mostrou-se claramente que é possível, através de processos químicos otimizados, separar os elementos terras raras e sintetizar uma fase pirocloro específica de fórmula TR2Ce2O7. Esta “fase extraída" pode ser obtida diretamente, de baixo custo, baseado em sistemas complexos feitos de minerais naturais e resíduos, como a monazita. Além disso, este método é aplicado a matérias de "custo zero", que é o caso dos resíduos, tornando um método de preparação de fases útil para aplicações de alta tecnologia.

Na década de 70 operou-se no IPEN/CNEN-SP uma instalação piloto para estudos do processamento de diferentes concentrados de tório obtidos do tratamento químico da monazita com intuito da obtenção de compostos de tório de pureza nuclear. Esta instalação passou a operar em escala industrial em 1985, gerando em torno de 25 toneladas de resíduo até meados de 2002, quando encerrou suas atividades. Este resíduo contendo tório e terras raras foi denominado Retoter (Resíduo de Tório e Terras Raras) e armazenado no galpão de Salvaguardas do IPEN. O presente trabalho estuda o tratamento deste resíduo, visando questões ambientais, radiológicas e tecnológicas. Estudaram-se dois processos cromatográficos para a separação do tório das terras raras. Um deles, a cromatografia de extração, onde o agente extrator fosfato de tri-n-butila foi suportado em resinas poliméricas Amberlite XAD16. O outro processo, estudado para fins comparativos, já que o material utilizado na cromatografia de extração é inédito no que diz respeito à separação do tório, foi a cromatografia de troca iônica utilizando resinas catiônicas fortes DOWEX 1-X8. Estudou-se, também, o processo cromatográfico de extração com o agente extrator DEHPA suportado em Amberlite XAD16 para o fracionamento, em grupos, dos elementos das terras raras. O tório foi separado com elevado grau de pureza para fins estratégicos e as terras raras recuperadas, livres de tório, foram testadas como catalisadores na reforma de etanol para a geração de hidrogênio, o qual é utilizado em células a combustível para a geração de energia elétrica. / In the 70s a pilot plant for studies of different concentrates processing obtained from the chemical processing of monazite was operated at IPEN / CNEN-SP, with a view to obtaining thorium of nuclear purity. This unity was operated on an industrial scale since 1985, generating around 25 metric tons of residue and was closed in 2002. This waste containing thorium and rare earths was named Retoter (Rejeito de Tório e Terras Raras, in portuguese) and stored in the IPEN Safeguards shed. This paper studies the treatment of the waste, aimed at environmental, radiological and technology. Were studied two cases for the chromatographic separation of thorium from rare earths. One of them was the chromatographic extraction, where the extracting agent tributyl phosphate was supported on polymeric resins Amberlite XAD16. The other method is studied for comparison purposes, since the material used in chromatographic extraction is unprecedented with regard to the separation of thorium, was the ion-exchange chromatography using DOWEX 1-X8 strong cationic resin. Was studied also the chromatographic process of extraction with the extracting agent DEHPA supported on Amberlite XAD16 for the fractionation in groups of rare earths elements. Thorium was separated with high purity for strategic purposes and rare earths recovered free from thorium, were tested as a catalyst for ethanol reforming to hydrogen obtaining which is used in fuel cells for power generation.

Sensores ópticos possibilitam a determinação da temperatura de maneira rápida e à distância, em ambientes onde os sensores de contato padrão se mostram ineficientes, como centrais elétricas (fortes campos eletromagnéticos), circuitos eletrônicos e células biológicas (escala micrométrica). Estes dispositivos são baseados em variações de uma propriedade óptica de um dado material devido à variação de temperatura. A técnica da razão da intensidade de fluorescência (FIR) faz uso da variação das intensidades relativas das emissões de dois níveis termicamente acoplados de um centro emissor, muitas vezes um íon terra-rara trivalente. O neodímio (Nd3+) é comumente empregado por apresentar emissões na janela biológica óptica do infravermelho próximo. Neste trabalho, vidros fluorofosfatos dopados com Nd3+ são utilizados como materiais para determinação da temperatura através da FIR. As emissões são coletadas por uma fibra óptica conectada a um espectrômetro portátil, cujos espectros medidos são analisados por um software. Este sistema permite a determinação em tempo real das razões das intensidades de fluorescência e, consequentemente, da temperatura. Sensibilidades de até 1,96%/K são obtidas para a razão entre as emissões do Nd3+ em 800 e 870 nm. Já o uso da razão entre as intensidades das emissões em 750 e 870 nm resulta em sensibilidades que chegam a 2,46%/K. A adição de itérbio (Yb3+) aos vidros faz com que a sensibilidade chegue a 2,77%/K quando emissões de ambos os íons são comparadas. O papel dos fônons na transferência de energia entre os íons é analisado. Os valores de razão de fluorescência obtidos a partir da análise pela teoria de Judd-Ofelt são aproximadamente 25% inferiores aos obtidos experimentalmente, não permitindo, neste sistema, o cálculo a priori da curva de calibração do sensor. / Optical sensors enable fast and long-distance temperature measurements in environments where standard contact sensors are ineffective, such as power stations (strong electromagnetic fields), electronic circuits and biological cells (sub-micron scale). These devices are based on temperature induced changes in optical properties of a given material. The fluorescence intensity ratio technique (FIR) makes use of the relative emission intensities variation of two thermally coupled levels of an emission center, usually a trivalent rare-earth ion. Neodymium (Nd3+) is commonly employed as its emissions lie in the near-infrared biological optical window. Here, Nd3+-doped fluorophosphate glasses are employed as a temperature sensing material through the use of FIR. The emissions are collected by an optical fiber connected to a portable spectrometer, whose measured spectra are analyzed by a software. This system enables real-time determination of the fluorescence intensity ratios and, therefore, the temperature. Sensibilities as high as 1.96%/K are obtained through the ratio between 800 and 870 nm Nd3+ emissions. The use of the emission ratio between 750 and 870 nm results in 2,46%/K sensibilities. The addition of ytterbium (Yb3+) dopant to the glasses makes the sensibilities increase to 2,77%/K when the emissions from both ions are compared. The phonons role in the energy tranfer between the ions is analyzed. The fluorescence ratio values obtained via Judd-Ofelt analysis are approximately 25% lower than the experimentally obtained, thus preventing, in this system, a priori calculation of the sensors calibration curve.

Neodymium (Nd) isotopes have been increasingly used to trace the modern and past ocean circulation. This assumes that seawater Nd isotope ratios (εNd) effectively fingerprint different water masses and approximate expected values from water mass mixing. However, the decoupling of Nd isotopes and Nd concentration (the “Nd paradox”) in the water column, and the lack of understanding of sources and sinks of Nd, restrain our understanding of the “quasi-conservative” behavior of εNd in seawater. Nd is one of the lanthanide rare earth elements (REEs) with similar chemical characteristics that undergo some degree of fractionation. The shale-normalized REE patterns and REE ratios can be used to investigate potential sources/sinks of REEs. Combining REEs with εNd will provide additional information to study REE cycling in the ocean. To better understand the reliability of εNd as a water mass tracer, 17 high-resolution seawater profiles were sampled meridionally in the Southwest Atlantic (GEOTRACES GA02 Leg 3; RRS James Cook 057) and measured for εNd. This region involves the major water masses in the Atlantic Meridional Overturning Circulation: southward flowing North Atlantic Deep Water (NADW), northward flowing Antarctic Intermediate Water (AAIW) and Antarctic Bottom Water (AABW). Along the cruise track, there are potential sources (eolian dusts, marginal sediments, oceanic volcanism, and nepheloid layer) that could add external Nd to seawater and disturb the “quasi-conservative” behavior of εNd. Our results show strikingly that the Southwest Atlantic transect confirms “quasi-conservative” behavior of εNd in intermediate and deep water. Our evaluations of Nd isotopic deviations (ΔεNd) from conservative behavior show that out of 198 intermediate and deep samples, 49% of ΔεNd-values are within ± 0.25 εNd units (< analytical error: ± 0.30 εNd units) and 84% of ΔεNd-values are within ± 0.75 εNd units. Potential sources that could add external Nd to seawater from oceanic volcanism and the nepheloid layer do not show impact on seawater εNd. Terrigenous sources of Nd (e.g. eolian dusts from Africa and Patagonia, marginal sediments from South America) show influence on surface/subsurface water εNd but this εNd signature is not transferred to intermediate and deep water. To better understand the conservative vs. non-conservative behavior of REEs in the ocean, the dissolved REE concentrations were analyzed for the 17 seawater profiles in the Southwest Meridional Atlantic Transect (GEOTRACES GA02 Leg 3). The shale-normalized REE patterns are consistent with typical seawater patterns. To investigate whether and how much REE concentrations deviate from conservative water mass mixing, the REE concentration deviations were calculated for the intermediate and deep water. It is shown that within the SAMT, the intermediate and deep water REEs generally reflect water mass mixing and nearly conservative behavior. Along this transect, the potential sources that could add external REEs to seawater are dissolution of REEs from eolian dust to the surface/subsurface water, REEs released from dissolution of Fe-Mn oxides in the oxygen depleted zone, REEs from sediments near the continental margin, and dissolution of REEs from deep sea sediments. REEs and Nd isotopes of most intermediate and deep water masses passing the volcanic Rio Grande Rise (RGR) and Vitória-Trindade Ridge (VTR) do not show influence from RGR and VTR. REEs and Nd isotopes of the bottom water Lower Circumpolar Deep Water (LCDW) and AABW passing the RGR are influenced by dissolved REEs from the deep sea sediments. LCDW and AABW passing the VTR are influenced by dissolved REEs from the deep sea sediments as well as the volcanic VTR. In order to better understand the oceanic Nd cycling in the North Pacific, its sources and sinks in seawater must be better characterized. The high εNd of North Pacific Deep Water (NPDW, ~ −4) has been difficult to reconcile with the eolian inputs as reflected in surface waters (e.g. Jones et al., 2008), which have much lower εNd (~ −10), indicating potential addition of a component from Pacific volcanism. In order to constrain the REE sources in the North Pacific, we measured εNd and REEs of seawater from five stations across the subarctic North Pacific sampled by the Innovative North Pacific Experiment (INOPEX) Cruise SO202 (2009). In the surface water (~10 m), the highest εNd is observed at the station closest to the Aleutian-Kamchatka volcanic margin (Northwest station SO202-5), suggesting higher contribution of external REEs from volcanic ashes compared to the other stations. In the shallow water (100-400 m, depending on location), remineralization of REEs from volcanic ashes prevails over Asian dusts at Northwest station SO202-5 and near Japan stations SO202-44, 41, and 39, whereas remineralization of REEs from Asian dusts prevails over volcanic ashes at the Northeast station SO202-32 in the open ocean of the Alaska Peninsula. From the depths of North Pacific Intermediate Water (NPIW) to NPDW, seawater εNd and REEs show conservative water mass mixing of NPIW-NPDW. They also show conservative behavior along the water mass transport paths of NPIW and NPDW. Below the depths of NPDW, addition of external REEs is observed in the vertical profiles of εNd and REEs as well as along the transport path of LCDW. The potential sources that add external REEs to the bottom water are (1) sediments on the Kuril-Kamchatka-Aleutian volcanic margin along the LCDW transport path, and (2) sediments on the seafloor, both of which could interact with seawater and modify the seawater εNd and REE signatures.

Neste trabalho foram preparadas as amostras Al2O3:TR3+ (TR3+=Eu, Gd) pelos métodos cerâmico, combustão e Pechini, calcinadas de 400 - 1400 ºC. Os difratogramas de raios X sugerem que as amostras calcinadas em menores temperaturas apresentam-se como sistemas amorfos, que com a elevação da temperatura de calcinação transformam-se na fase cúbica das aluminas ativadas (&#947;-Al2O3). A partir de 1200 ºC forma-se a fase hexagonal de &#945;-Al2O3, altamente cristalina e termoestável. O tamanho dos cristalitos foi determinado pelo método de Scherrer a partir dos respectivos difratogramas. Em geral, os espectros no infravermelho de Al2O3:Eu3+ apresentaram estiramentos relativos aos grupos tetraédricos [AlO4] condensados e/ou isolados indicando a presença de fase &#947;-alumina. Foi também observada a existência de bandas em regiões de menores energias atribuídas às freqüências de estiramento de grupos octaédricos [AlO6] relativas à fase &#945;-alumina (coríndon). A Microscopia Eletrônica de Varredura (MEV) indicou que as partículas obtidas pelo método cerâmico apresentam menor tamanho e uma morfologia mais uniforme comparados com aquelas obtidas pelos métodos de combustão e Pechini. Os espectros de emissão (&#955; exc. = 320 nm) do sistema Al2O3:Gd3+ não apresentam as bandas finas oriundas dos íons Cr3+ observadas nos espectros da alumina não dopada, indicando que íon Gd3+ suprime a luminescência destes íons. Os espectros de excitação das amostras Al2O3:Eu3+ preparadas pelo três métodos apresentam uma banda larga atribuída aos defeitos da matriz Al2O3 e à banda LMCT do O&#8594;Eu3+, enquanto que as bandas finas são atribuídas às transições 7F0#&8594;5DJ, 5HJ e 5LJ oriundas do íon Eu3+. Os espectros de emissão dos sistemas Al2O3:Eu3+ (1%), obtidos pelos métodos de combustão, cerâmico e Pechini, e calcinados de 400 - 1100 ºC (&#955;exc. = 394 nm) apresentam bandas alargadas atribuídas às transições 5D0&#8594;7FJ do íon Eu3+, sugerindo a ocupação de diferentes sítios de simetria neste sistema evidenciado através do alargamento inomogêneo das bandas atribuídas às transições 4f-4f do íon terra rara. A presença da inomogeneidade das transições eletrônicas 5D0&#8594;7FJ para Al2O3:Eu3+ (1%) calcinada de 400 a 1000 ºC sugere que este sistema apresenta predominância da fase gama (&#947;-Al2O3:Eu3+). A conversão da &#947;-Al2O3 (fase metaestável) em &#945;-Al2O3 (fase estável - coríndon) promove alterações significativas nos espectros de emissão (&#955;exc. = 394 nm). As amostras calcinadas de 1100 a 1400 ºC exibem um pico fino de alta intensidade (695 nm) atribuídas à linha R do íon Cr3+. A curva de decaimento luminescente do nível emissor 5D0 apresentou um comportamento bi-exponencial indicando que o íon Eu3+ encontra-se em um ambiente químico com diferentes sítios de simetria. O sistema Al2O3:Eu3+ preparado pelo método de combustão (400 - 1100 ºC) apresenta um aumento nos valores dos parâmetros de intensidades &#937;2 com o aumento da temperatura de calcinação promovendo uma elevação do caráter covalente da interação metal-doador. Os valores da eficiência quântica de emissão (&#951;) dos sistemas Al2O3:Eu3+ apresentam-se maiores comparados com outros sistemas vítreos. Observa-se que as coordenadas CIE dos compostos Al2O3:Eu3+ localizam-se próximas ao vértice correspondente à cor vermelha sugerindo uma grande contribuição desta cor. / In this work, Al2O3:TR3+ (TR3+=Eu, Gd) samples were prepared by ceramic, combustion and Pechini methods annealed at the temperature range of 400 - 1400 ºC. X-Ray diffraction -XRD patterns suggest that samples heated at lower temperatures are amorphous systems, but when the temperature increases, a change in the cubic phase of activated alumina (&#947;-Al2O3) is observed. The &#945;-Al2O3 phase showed high crystallinity and thermostability annealed at 1200 ºC. Crystallite size was determined by Scherrer\'s method using XRDs. In general, infrared spectra of Al2O3:Eu3+ show stretching frequencies related to condensed and/or isolated tetrahedral groups [AlO4] indicating the presence of &#947;-alumina phase. It was observed the existence of bands in lower energies attributed to stretching frequencies of octahedral groups [AlO6] from &#945;-alumina phase (corundum). The scanning electron microscopy (SEM) suggests that particles obtained by ceramic method show the smallest size and the most uniform morphology compared to those prepared by combustion and Pechini methods. Emission spectra (&#955; exc. = 320 nm) of AlAl2O3:Gd3+ system present no narrow bands arising from Cr3+ ions observed in the spectra of non-doped alumina indicating luminescence quenching by Gd3+ ion. Excitation spectra of Al2O3:Eu3+ samples prepared by three methods present a broad band attributed to defects of Al2O3 matrice and to LMCT state of O&#8594;Eu3+, on the other hand, the narrow bands are assigned to 7F0&#8594;5DJ, 5HJ and 5LJ transitions arising from Eu3+ ion. Emission spectra of Al2O3:Eu3+ (1%) system prepared by combustion, ceramic and Pechini methods, annealed from 400 to 1100 ºC (&#955;exc. = 394 nm) show broad bands for 5D0&#8594;7FJ transitions of Eu3+ ion suggesting that this ion is in different symmetry sites indicated by inhomogeneous line broadening of bands attributed to 4f-4f transition from rare earth ion. The presence of inhomogeneity of 5D0&#8594;7FJ transitions for Al2O3:Eu3+ (1%) annealed from 400 to 1000 ºC suggests that this system presents predominantly the &#947;-alumina phase. The conversion of &#947;-Al2O3 (metastable phase) to &#945;-Al2O3 (stable phase - corundum) changes significantly their emission spectra (&#955;exc. = 394 nm). The samples annealed from 1100 to 1400 ºC, exhibited a high intensity narrow peak around 695 nm assigned to R lines of Cr3+ ion. Luminescence decay curves of 5D0 emitter level have a bi-exponential behavior indicating that Eu3+ ion is found in a chemical environment with different symmetry sites. The Al2O3:Eu3+ system prepared by combustion method at 400 -1100 ºC presents an increase in the &#937;2 intensity parameter values with the increase of annealing temperatures enhancing the covalent character of metal-donator interaction. The values of emission quantum efficiencies (&#951;) of Al2O3:Eu3+ are higher than those for vitreous systems. CIE coordinates of Al2O3:Eu3+ are located near the corner corresponding to monochromatic red color.

Neste trabalho foram preparadas as amostras Al2O3:TR3+ (TR3+=Eu, Gd) pelos métodos cerâmico, combustão e Pechini, calcinadas de 400 - 1400 ºC. Os difratogramas de raios X sugerem que as amostras calcinadas em menores temperaturas apresentam-se como sistemas amorfos, que com a elevação da temperatura de calcinação transformam-se na fase cúbica das aluminas ativadas (&#947;-Al2O3). A partir de 1200 ºC forma-se a fase hexagonal de &#945;-Al2O3, altamente cristalina e termoestável. O tamanho dos cristalitos foi determinado pelo método de Scherrer a partir dos respectivos difratogramas. Em geral, os espectros no infravermelho de Al2O3:Eu3+ apresentaram estiramentos relativos aos grupos tetraédricos [AlO4] condensados e/ou isolados indicando a presença de fase &#947;-alumina. Foi também observada a existência de bandas em regiões de menores energias atribuídas às freqüências de estiramento de grupos octaédricos [AlO6] relativas à fase &#945;-alumina (coríndon). A Microscopia Eletrônica de Varredura (MEV) indicou que as partículas obtidas pelo método cerâmico apresentam menor tamanho e uma morfologia mais uniforme comparados com aquelas obtidas pelos métodos de combustão e Pechini. Os espectros de emissão (&#955; exc. = 320 nm) do sistema Al2O3:Gd3+ não apresentam as bandas finas oriundas dos íons Cr3+ observadas nos espectros da alumina não dopada, indicando que íon Gd3+ suprime a luminescência destes íons. Os espectros de excitação das amostras Al2O3:Eu3+ preparadas pelo três métodos apresentam uma banda larga atribuída aos defeitos da matriz Al2O3 e à banda LMCT do O&#8594;Eu3+, enquanto que as bandas finas são atribuídas às transições 7F0#&8594;5DJ, 5HJ e 5LJ oriundas do íon Eu3+. Os espectros de emissão dos sistemas Al2O3:Eu3+ (1%), obtidos pelos métodos de combustão, cerâmico e Pechini, e calcinados de 400 - 1100 ºC (&#955;exc. = 394 nm) apresentam bandas alargadas atribuídas às transições 5D0&#8594;7FJ do íon Eu3+, sugerindo a ocupação de diferentes sítios de simetria neste sistema evidenciado através do alargamento inomogêneo das bandas atribuídas às transições 4f-4f do íon terra rara. A presença da inomogeneidade das transições eletrônicas 5D0&#8594;7FJ para Al2O3:Eu3+ (1%) calcinada de 400 a 1000 ºC sugere que este sistema apresenta predominância da fase gama (&#947;-Al2O3:Eu3+). A conversão da &#947;-Al2O3 (fase metaestável) em &#945;-Al2O3 (fase estável - coríndon) promove alterações significativas nos espectros de emissão (&#955;exc. = 394 nm). As amostras calcinadas de 1100 a 1400 ºC exibem um pico fino de alta intensidade (695 nm) atribuídas à linha R do íon Cr3+. A curva de decaimento luminescente do nível emissor 5D0 apresentou um comportamento bi-exponencial indicando que o íon Eu3+ encontra-se em um ambiente químico com diferentes sítios de simetria. O sistema Al2O3:Eu3+ preparado pelo método de combustão (400 - 1100 ºC) apresenta um aumento nos valores dos parâmetros de intensidades &#937;2 com o aumento da temperatura de calcinação promovendo uma elevação do caráter covalente da interação metal-doador. Os valores da eficiência quântica de emissão (&#951;) dos sistemas Al2O3:Eu3+ apresentam-se maiores comparados com outros sistemas vítreos. Observa-se que as coordenadas CIE dos compostos Al2O3:Eu3+ localizam-se próximas ao vértice correspondente à cor vermelha sugerindo uma grande contribuição desta cor. / In this work, Al2O3:TR3+ (TR3+=Eu, Gd) samples were prepared by ceramic, combustion and Pechini methods annealed at the temperature range of 400 - 1400 ºC. X-Ray diffraction -XRD patterns suggest that samples heated at lower temperatures are amorphous systems, but when the temperature increases, a change in the cubic phase of activated alumina (&#947;-Al2O3) is observed. The &#945;-Al2O3 phase showed high crystallinity and thermostability annealed at 1200 ºC. Crystallite size was determined by Scherrer\'s method using XRDs. In general, infrared spectra of Al2O3:Eu3+ show stretching frequencies related to condensed and/or isolated tetrahedral groups [AlO4] indicating the presence of &#947;-alumina phase. It was observed the existence of bands in lower energies attributed to stretching frequencies of octahedral groups [AlO6] from &#945;-alumina phase (corundum). The scanning electron microscopy (SEM) suggests that particles obtained by ceramic method show the smallest size and the most uniform morphology compared to those prepared by combustion and Pechini methods. Emission spectra (&#955; exc. = 320 nm) of AlAl2O3:Gd3+ system present no narrow bands arising from Cr3+ ions observed in the spectra of non-doped alumina indicating luminescence quenching by Gd3+ ion. Excitation spectra of Al2O3:Eu3+ samples prepared by three methods present a broad band attributed to defects of Al2O3 matrice and to LMCT state of O&#8594;Eu3+, on the other hand, the narrow bands are assigned to 7F0&#8594;5DJ, 5HJ and 5LJ transitions arising from Eu3+ ion. Emission spectra of Al2O3:Eu3+ (1%) system prepared by combustion, ceramic and Pechini methods, annealed from 400 to 1100 ºC (&#955;exc. = 394 nm) show broad bands for 5D0&#8594;7FJ transitions of Eu3+ ion suggesting that this ion is in different symmetry sites indicated by inhomogeneous line broadening of bands attributed to 4f-4f transition from rare earth ion. The presence of inhomogeneity of 5D0&#8594;7FJ transitions for Al2O3:Eu3+ (1%) annealed from 400 to 1000 ºC suggests that this system presents predominantly the &#947;-alumina phase. The conversion of &#947;-Al2O3 (metastable phase) to &#945;-Al2O3 (stable phase - corundum) changes significantly their emission spectra (&#955;exc. = 394 nm). The samples annealed from 1100 to 1400 ºC, exhibited a high intensity narrow peak around 695 nm assigned to R lines of Cr3+ ion. Luminescence decay curves of 5D0 emitter level have a bi-exponential behavior indicating that Eu3+ ion is found in a chemical environment with different symmetry sites. The Al2O3:Eu3+ system prepared by combustion method at 400 -1100 ºC presents an increase in the &#937;2 intensity parameter values with the increase of annealing temperatures enhancing the covalent character of metal-donator interaction. The values of emission quantum efficiencies (&#951;) of Al2O3:Eu3+ are higher than those for vitreous systems. CIE coordinates of Al2O3:Eu3+ are located near the corner corresponding to monochromatic red color.

One of the fundamental properties of bulk metals is the cancellation of electric fields. The free charges inside of a metal will move until they find an arrangement where the internal electric field is zero. This implies that the electric dipole moment of a metal particle should be exactly zero, because an electric dipole moment requires a net separation of charge and thus a nonzero internal electric field. This thesis is an experimental study to see if this property continues to hold for tiny sub- nanometer metal particles called clusters (2 - 200 atom, R < 1 nm). We have measured the electric dipole moments of metal clusters made from 15 pure elements using a molecular beam electric deflection technique. We find that the observed dipole moments vary a great deal across the periodic table. Alkali metals have zero dipole moments, while transition metals and lanthanides all have dipole moments which are highly size dependent. In most cases, the measured dipole moments are independent of temperature (T = 20 - 50 K), and when there is a strong temperature dependence this suggests that there is a new state of matter present. Our interpretation of these results are that those clusters which have a non- zero dipole moment are non-metallic, in the sense that their electrons must be localized and prevented from moving to screen the internal field associated with a permanent dipole moment. This interpretation gives insight to several related phenomena and applications. We briefly discuss an example cluster system RhN where the measured electric dipole moments appear to be correlated with a the N2O reactivity. Finally, we discuss a series of magnetic deflection experiments on lanthanide clusters (Pr, Ho, Tb, and Tm). The magnetic response of these clusters is very complex and highly sensitive to size and temperature. We find that PrN (which is non-magnetic in the bulk) becomes magnetic in clusters and TmN clusters have magnetic moments lower than the atomic value as well as the bulk saturation value implying that the magnetic order in the cluster involves non-collinear or antiferromagnetic order. HoN and TbN show very similar size dependent trends suggesting that these clusters have similar structures.

A combination of 169Tm-Mo??ssbauer spectroscopy and inelastic neutron scattering (INS) has been used to investigate the crystal field (CF) interaction at the rare earth site for the tetragonal series RT2Si2 (where R = rare earth) and the orthorhombic series RNiAl4. Single phase specimens were prepared in an argon arc furnace and characterised using x-ray powder diffraction, specific heat and magnetic measurements. For the RT2Si2 series previous investigations were extended to include T = Mn and Cr whose sub-lattices are antiferromagnetic well above room temperature. However, the rare earth sub-lattices were confirmed to order close to liquid helium temperature. With the assistance of the lattice electric field gradient (EFG) for isostructural GdCr2Si2 (determined elsewhere using 155Gd-Mo??ssbauer spectroscopy) and the within-rank CF parameter ratios for HoCr2Si2 (determined elsewhere using INS), the experimental 169Tm quadrupole interaction data were analysed to arrive at CF parameters for the Tm3+ site in TmCr2Si2. The final CF parameters match well with the trend observed for other members of the series RT2Si2 (T = Fe, Co, Ni, Cu). CF schemes were also determined for Tm3+ in TmMn2Si2 and Er3+ in both ErCr2Si2 and ErMn2Si2. For the RNiAl4 series, TmNiAl4 was determined to be antiferromagnetic below TN = 4.7 K with the 169Tm-Mo??ssbauer spectra retaining a magnetic appearance up to 80 K due to the effect of slow spin-lattice relaxation. The relaxation data are consistent with a well-isolated ground state doublet (or pseudo-doublet) whose eigenfunctions have high components of mJ = ??6 states and with the relaxation proceeding via an excited state at 350 K. Because of the relaxation effect, the 169Tm-Mo??ssbauer data could not be interpreted in terms of CF parameters in the usual way. Instead, the INS spectra recorded for ErNiAl4 were analysed using a novel semi-empirical approach that coupled rank 2 CF parameters converted from the EFG tensor for isostructural GdCr2Si2 (determined elsewhere using 155Gd-Mo??ssbauer spectroscopy) with simple point-charge model calculations of the rank 4 and 6 within-rank CF parameter ratios. The first full set of CF parameters for this series was then determined for the Er3+ site in ErNiAl4.