O estudo dos processos de transferência de energia por íons opticamente ativos em matrizes rígidas vem recebendo bastante atenção por parte de pesquisadores, devido a importância destes processos em dispositivos de estado sólido, tais como laseres e materiais ópticos e eletrônicos. Esses materiais luminescentes (luminóforos) em solução aquosa podem ainda ser muito úteis como sensores ou sondas para análises de biomateriais. Neste contexto, íons de terras raras (TR) e as ciclodextrinas (CD) são muito importantes, já que podem participar no estado sólido e em solução. Algumas TRs – como o európio e o térbio – apresentam a propriedade da luminescência, enquanto que as CDs possuem uma cavidade apolar que pode incorporar moléculas (ou partes delas) em seu interior e protegê-las das moléculas do solvente, proporcionando assim uma matriz hidrofílica rígida em solução. Neste trabalho foi realizado o estudo de complexos de íons terras raras incorporados na cavidade da α-CD e, posteriormente, o estudo desses compostos (TR/α-CD) incorporados em matrizes inorgânicas através do método sol-gel. Inicialmente, foram sintetizados e caracterizados complexos de terras raras com β-dicetonas. A solubilização dos complexos em solução aquosa foi realizada pela incorporação destes na cavidade apolar da α-CD. Foram obtidos espectros de excitação, emissão e valores de tempo de vida do íon TR em ambiente aquoso. Observou-se que os íons apresentaram suas transições características no novo ambiente. Posteriormente, os compostos de α-CD foram estudados em matrizes inorgânicas, obtidas através do método sol-gel. Após a dopagem, a estabilidade térmica do composto aumentou e as linhas espectrais dos íons TR apresentaram-se mais definidas. / In recent years, there has been considerable research on the study of energy transfer process by active optically ions due to their great importance in solid state devices, e.g., lasers and optic-electronic materials. These luminescent materials (phosphors) in aqueous solution can also be very useful as sensors or probe in biomaterials analysis. In this context, the interest on rare earth ion (RE), as well as cyclodextrin (CD) in such systems are increasing due to their compatibility wish solid state and aqueous media. Some RE, like europium and terbium, present luminescent properties, while the CD’s have an apolar/hydrophobic cavity that can incorporate molecules, protecting them from solvent entities and resulting na a rigid hydrophobic matrix in solution. In the present work was performed the study of RE complexes incorporate into α-CD hydrophobic cavity, and then, the investigation on RE/α-CD compounds incorporated in inorganic matrices through the sol-gel method. First, RE complexes with β-diketones were synthesized and characterized. The solubilization of these complexes in aqueous solution was achieved by their incorporation into α-CD hydrophobic cavity. Excitation and emission spectra as well as lifetime measurements were performed for RE ions in aqueous media. It was observed that the RE ions present their characteristic transitions in the new environment. Therefore, RE/α-CD compounds in inorganic matrices obtained by sol-gel method were also studied. After doping, the thermal stability of these compounds increase and the detected RE ions emission lines presented a better definition than the ones in the α-CD incorporate RE/β-diketones in aqueous medium.

Este trabalho enfocou o levantamento de informações químicas e mineralógicas de detalhe em amostras de depósitos alcalinos e alcalino carbonatíticos brasileiros contento terras raras, de modo a fornecer subsídios para o desenvolvimento de processos de aproveitamento. Estes depósitos apresentam elevados volumes de recursos, baixos teores de elementos de terras raras (essencialmente terras raras leves) e elevada complexidade mineralógica. As amostras estudadas são provenientes de depósitos lateríticos, com teor total de óxidos de terras raras entre 1,27 e 6,45%, sendo a monazita o principal mineral portador desses elementos, exceto em uma das amostras, onde é predominante a bastnaesita; como minerais traços estão presentes cerianita, xenotima e um fosfato de escândio. Os minerais de terras raras tendem a concentrar-se em direção às frações granulométricas mais finas, mostram d50 de 15 µm nas frações acima de 0,008 mm e chegam a valores inferiores a 0,1 µm abaixo da mesma. Esses minerais ocorrem preferencialmente em íntimas associações com a ganga, sendo que valores superiores a 60% de liberação (em área) são observados apenas nas frações menores que 0,020 mm. O potencial de concentração desses minerais foi avaliado por separações físicas e extração hidrometalúrgica. Separações físicas em líquidos densos e magnéticas não possibilitaram a obtenção de produtos enriquecidos em terras raras. O resultado mais promissor refere-se à possibilidade de remoção de um produto contaminante magnético nas frações retidas em 0,020 mm e que responde por 30% do total de Fe2O3 contido nas amostras (em média), sem perdas significativas das terras raras. A condição experimental otimizada para a dissolução seletiva dos minerais de terras raras em meio ácido foi estabelecida a partir de um planejamento experimental baseado em princípios estatísticos. Para o material cominuído abaixo de 0,30 mm, a solubilização dos óxidos de terra raras é de 77%, considerando-se ácido sulfúrico concentrado, reduzida porcentagem de sólidos, temperatura ambiente e tempo de 4 horas. Maiores níveis de solubilização das terras raras podem ser alcançados, mas juntamente com elevação da solubilização da ganga. / This work focused on the acquisition of chemical and mineralogical detailed information in samples from Brazilian alkaline and alkaline-carbonatitic deposits containing rare earths, in order to provide subsidies for process development. These deposits present high volumes of resources, low contents of rare earth elements (essentially light rare earths) and high mineralogical complexity. The studied samples are lateritic materials, with a total content of rare earth oxides between 1.27 and 6.45%, being monazite the main rare earth bearing mineral, except in one of the samples, where bastnaesite is predominant; cerianite, xenotime and a scandium-phosphate occur as trace. Rare earth minerals tend to enrich toward the finest sieve fractions with an medium grain size of 15 µm in the fractions greater than 0.008 mm and decreasing below 0.1 µm in finer fractions. These minerals occur preferentially in intimate associations with the gangue; liberation greater than 60% (in area) are observed under 0.020 mm fractions. The concentration potential of these minerals was evaluated through physical separation and hydrometallurgical extraction. Physical separations (heavy liquid and magnetic) did not succeed in obtaining products enriched in rare earths. The most promising result were the possibility of removing magnetic phases above 0.020 mm (responsible for 30%, on average, of the total Fe2O3 contained in the samples) without significant losses of rare earths. The rare earths acid leaching protocols and conditions were established by statistical experimental design. For samples comminuted below 0.30 mm, the best rare earths solubilization (77%) and with minimum gangue leaching was obtained in concentrate sulfuric acid, low solids concentration, environmental temperature and four hours of reaction. Higher levels of rare earths solubilization can be achieved, however accompanied by higher gangue solubilization.

Orientador: Keizo Yukimitu / Resumo: Com a crescente populacional a demanda pelos polímeros aumentou significativamente, levando assim a pesquisas cientificas visando adequar materiais as nossas necessidades. O PMMA ou acrílico é muito utilizado em nosso cotidiano, sendo um material muito versátil com aplicabilidade em diversos setores. O intuito deste trabalho foi realizar a produção de um filme de acrílico [Poli(metil-metacrilato)] isento de bolhas e transparente, a qual tivesse uma repetibilidade. Foi realizada a dopagem com terras raras, sendo o Óxido de Érbio e o Óxido de Itérbio escolhidos como dopantes em diferentes concentrações de gramas/mol por gramas/mol (0 % referência, 5 %, 10%, 15% e 20 %). Logo após foi feita a caracterização dos filmes, determinando o índice de refração das amostras utilizando o Interferomêtro de Michelson com laser He-Ne (vermelho) de comprimento de onda de 632,8 nm. Notamos que o índice de refração do PMMA na amostra de referência aumentou gradativamente com as dopagens, o laser diodo na cor verde de comprimento de onda de 532 nm também foi utilizado e os resultados demostraram comportamentos similares. A Espectroscopia no Infravermelho por Transformada de Fourier (FTIR) foi realizada, observando o aparecimento de picos característicos dos elementos dopantes nas amostras e que esses picos aumentavam conforme a concentração de dopagem aumentava. A Difração de Raios-X (DRX) nos mostrou a incidência picos de cristalinidade referentes aos elementos dopantes em contraste com o espec... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: With the growing population demand for polymers has increased significantly, leading to scientific research aimed at adapting materials to our needs. PMMA or acrylic is widely used in our daily lives, being a very versatile material with applicability in several sectors. The purpose of this work was to produce an acrylic film [Poly (methyl-methacrylate)] which had a repeatability. Rare earth doping was performed, with Erbium Oxide and Ytterbium Oxide chosen as dopants in different concentrations of grams / mole per gram / mole (0% reference, 5%, 10%, 15% and 20%). After the characterization of the films, determining the refractive index of the samples using the Michelson Interferometer with He-Ne (red) laser of wavelength of 632.8 nm, we noticed that the refractive index of the PMMA in the sample of reference period increased gradually with doping, the green diode laser wavelength of 532 nm was also used and the results demonstrated similar behaviors. Fourier Transform Infrared Spectroscopy (FTIR) was performed, observing the appearance of characteristic peaks of the dopant elements in the samples and that these peaks increased as the doping concentration increased. X-ray Diffraction (XRD) showed us the incidence of crystallinity peaks relative to the dopant elements in contrast to the normal PMMA spectrum demonstrating the insertion of the rare earths into the matrix structure. / Mestre

Neste trabalho são relatadas as propriedades fotoluminescentes e eletroluminescentes dos compostos de β-dicetonato de terras raras trivalentes (onde TR3+ = Eu, Sm e Gd) contendo ligantes fosfinóxidos e sulfóxidos. A preparação dos complexos foi feita pela reação do precursor β-dicetonato hidratado [TR(TTA)3(H2O)2] (TTA = tenoiltrifluoroacetonato) com os ligantes fosfinóxidos [trifenilfosfinóxido (TPPO)] e sulfóxidos [dibenzilsulfóxido (DBSO) e difenilsulfóxido (DPSO)] em solução etanólica. Os complexos foram caracterizados por análise elementar, análise termogravimétrica, DRX pelo método do pó e monocristal e espectroscopia IV. Os dados de microanálise e titulação complexométrica evidenciaram que os complexos apresentam a fórmula geral [TR(TTA)3(L)2]. As curvas TG/DTG apresentaram etapas de decomposição térmica bem definidas para os compostos anidros e indicaram que os complexos sintetizados mostram maior estabilidade térmica que o complexo hidratado. Os espectros de absorção na região do infravermelho indicaram que a coordenação do ânion TTA- e ligantes fosfinóxidos e sulfóxidos ao íon TR3+ ocorre através dos átomos de oxigênio. Através da técnica de difratometria de raios-X por monocristal elucidou-se a estrutura molecular do complexo bis(trifenilfosfinóxido )-tris(tenoilfluoracetonato )európio(III) [Eu(TTA)3(TPPO)2]. O complexo em questão apresenta sistema triclínico, com grupo espacial P-1. Oito átomos de oxigênio estão coordenados ao íon central e a esfera de coordenação apresenta-se como um antiprisma quadrado com moléculas de TPPO ocupando faces opostas. Os espectros de emissão mostram que os desdobramentos das transições 5D0→7Fj (J = 0 a 4) para os complexos de Eu3+ e 4G5/2 → 6HJ (J = 5/2-11/2) para o Sm3+ obedecem à regra de seleção do número máximo de componentes, sugerindo um grupo pontual de baixa simetria. O alto valor dos parâmetros de intensidade Ω2 dos complexos de Eu3+ reflete o comportamento hipersensível da transição 5D0→7F2, indicando que o íon Eu3+ encontra-se em um ambiente químico altamente polarizável. As curvas de decaimento, para os sistemas com os íons Eu3+ e Sm3+, ajustam-se a uma exponencial de primeira ordem, sugerindo que não há outro processo de depopulação para o nível 5D0 e o valor do tempo de vida indica que o processo de transferência de energia é bastante operante. Os compostos preparados com os ligantes sulfóxidos e fosfinóxidos apresentam maior tempo de vida em relação ao complexo [Eu(TTA)3(H2O)2], este fato está associado a ausência de processos de desativação não radiativa referente ao acoplamento vibrônico com as moléculas de água. Os complexos contendo ligantes sulfóxidos e fosfinóxidos apresentam maiores valores de eficiência quântica e rendimento quântico de emissão experimental em relação ao complexo hidratado devido à substituição das moléculas de água, extinguindo assim, a supressão da luminescência pelos osciladores OH. O espectro de fosforescência do composto [Gd(TTA)3(TPPO)2] apresenta bandas referentes aos estados tripletos (T) do TTA- (~ 525 nm). Estas bandas não são observadas no espectro de emissão dos complexos de Eu3+ e Sm3+ indicando que a transferência de energia do estado T de menor energia do TTA- para os níveis emissores 5D0 (Eu3+) e 4G5/2 (Sm3+) é bastante eficiente. O complexo [Eu(TTA)3(TPPO)2] foi utilizado como camada emissora na construção de dispositivos eletroluminescentes com estruturas: ITO/TPD/[Eu(TTA)3(TPPO)2]/Alq3/Al,ITO/MTCD/[Eu(TTA)3(TPPO)2]/Alq3/Al e ITO/MTCD/[Eu(TTA)3(TPPO)2]/Al apresentaram valor máximo de eficiência EL em torno de 0,0011 cd/A em 23 V. Os espectros EL apresentaram emissão características das transições 5D0→7FJ oriundas do íon Eu3+. As coordenadas da Comissão Internacional de l\'Eclairage (CIE) foram determinadas e mostraram que os dispositivos emitem cor vermelha monocromática. / In this work the photo and electroluminescent properties of the trivalent rare earth (RE3+ = Eu, Sm and Gd) β-diketonate compounds with phosphine oxide and sulfoxide ligands are related. The TR3+ complexes were prepared by the reaction between the hydrated β-diketonate [TR(TTA)3(H2O)2] (TTA = thenoyltrifluoroacetonate) and the phosphine oxides and sulfoxides ligands in ethanolic solution. The complexes were characterized by elemental analysis, thermogravimetric analysis, XRD by powder and monocrystal methods, and IR spectroscopy. The microanalysis and complexometric titration data evidenced that complexes present the general formula [RE(TTA)3(L)2] (where L = triphenilphosphine oxide TPPO, diphenilsulfoxide DPSO and dibenzilsulfoxide DBSO). The TG/DTG curves ofthe anhydrous compounds showed well-defined stages with higher thermal stability when compared to the hydrated complex. The absorption spectra in the infrared region showed that the coordination of TTA anion and ligands to RE3+ ions occurs through the oxygen atoms. The molecular structure of the complex europium (III) tris(α-tenoyltrifluoroacetonate) bistriphenylphosphine oxide [Eu(TTA)3(TPPO)2] was elucidated utilizing the monocrystal X-ray difractometry technique. This complex has a triclinic system, with spatial group P-1, where eight oxygen atoms are coordinated to the rare earth ion and the coordination polyhedron which is best approximated as a squared antiprism whereas there are two TPPO molecules occupying the opposite faces. The emission spectra showed that the 5D0→7Fj (J = 0-4) and 4G5/2 → 6HJ (J = 5/2-11/2) transitions of the europium and samarium complexes, respectively splitting in the maximum number components, indicating that the rare earth ions are in a low site symmetries. The high value of the intensity parameters Ω2 of the Eu3+ complexes reflect the hypersensitive behavior of the 5D0→7F2 transition indicating that the Eu3+ ion is in a highly polarizable chemical environment. The luminescence decay curves of the systems containing Eu3+ and Sm3+ ions, adjust to a first order exponential, suggesting that there is no other channel for the depopulation to the level 5D0 and the value of lifetime indicate that the transfer energy process is operant. The [Eu(TTA)3(TPPO)2] has a higher lifetime value than europium tris(thenoyltrifluoroacetonate) dihydrate [Eu(TTA)3(H2O)2] due to the absence of the deactivation channel non-radiative by the vibronic coupling from the water molecules. It has been observed an increase in the emission quantum yield ( and emission quantum efficiency) of β-diketonate complexes when the TPPO, DPSO and DBSO ligands substitute the two water molecules. The phosphorescence spectrum of the [Gd(TTA)3(TPPO)2] complex shows bands referent to the triplet states (T) of the TTA-. These bands are not observed in the emission spectra of the Eu3+ e Sm3+ complexes, corroborating that the energy transfer from the lower energy T of the TTA- to the emitting level 5D0 (Eu3+) e 4G5/2 (Sm3+) is very effective. The [Eu(TTA)3(TPPO)2] complex was utilized as emitting layer in the construction of electroluminescent devices with the structure ITO/TPD/[Eu(TTA)3(TPPO)2]/Alq3/Al, ITO/MTCD/[Eu(TTA)3(TPPO)2]/Alq3/Al and ITO/MTCD/[Eu(TTA)3(TPPO)2]/Al and showed high efficiency around 0.0011 cd/A at 23 V The EL spectra presented characteristic emission originated from the Eu3+ ion. The chromaticity coordinates of the Commission Internationale de l\'Eclairage (CIE) was determined and showed that the constructed devices emit a monochromatic red light.

A produção de energia limpa e renovável é uma preocupação crescente da sociedade. Dentre as alternativas para produção de energia estão as células a combustível. Dentre os vários tipos de células, existem as PEMFC (Proton Exchange Membran Fuel Cell) que possuem vantagem de operar em baixa temperatura e podem utilizar como combustível hidrogênio ou álcoois. Porém as células PEM que utilizam álcool como combustível, ainda apresentam um rendimento inferior aquelas que operam com hidrogênio, além disso essas células requerem platina ou outros metais nobres porque somente estes materiais são relativamente estáveis nestas condições de pH. Nos últimos anos as células combustíveis alcalinas tem ganhado destaque devido à maior estabilidade dos eletrocalisadores, aumentando a possibilidade de utilização de metais não nobres ou óxidos metálicos. Neste trabalho, catalisadores do tipo Pt/C-CeO2 foram sintetizados sobre carbono de alta área superficial, variando-se a quantidade de CeO2 entre 0 a 10%. Os eletro-catalisadores contendo menor quantidade de óxidos apresentaram maior atividade frente a oxidação do etanol em meio básico. / The production of clean and renewable energy is a growing concern of society. Among the alternatives for energy production are fuel cells. Among the various types of cells, there are PEMFCs (Proton Exchange Membranes) which have the advantage of operating at low temperature and can use hydrogen or alcohols as fuel. However, PEM cells that use alcohol as fuel still have lower yields than those operating on hydrogen. In addition, these cells require platinum or other noble metals because only these materials are relatively stable under these pH conditions. In recent years alkaline fuel cells have gained prominence due to the greater stability of the electrocatalyst, increasing the possibility of using non-noble metals or metal oxides. In this work, catalysts like Pt-CeO2/C type were synthesized on carbon of high surface area, varying the amount of CeO2 between 0 and 10% (m/m). The electrocatalysts containing less oxides showed higher activity against the oxidation of ethanol in a basic medium.

On a global scale, the deployment of wind power plants is soaring. However, the availability of their construction materials could be a potential bottleneck, a problem rarely discussed in literature so far. Rare earth elements represent the most critical materials in terms of high economic importance, supply risk and environmental risk. This study therefore provides a market analysis of rare earths, ascertaining that geological scarcity is not the main problem. Instead, four kinds of market failure are identified: market power, co-production, by-production and negative externalities. Altogether, the market for rare earth metals is in a state of severe disequilibrium. Subsequently, an estimate of future rare earth demand patterns based on the wind power industry by 2050 reveals that the current level of supply is unlikely to be sufficient in the long run. To allow for a more elaborate analysis, two options of including a rare earth side condition in an integrated assessment model are finally suggested.

Rare-earth oxides used in oxide dispersion strengthening are known to provide excellent strength and deformability over ordinary dispersion strengthening. It has been suggested that this may be due to the development of molybdate compounds instead of pure dispersed oxide particles. These alloys are produced by dispersing particles of certain rare-earth oxides in a molybdenum matrix and forming the mixture into a composite ingot. During the high-temperature consolidation process, the oxides are converted into rare-earth molybdates. With subsequent processing, these molybdate phases undergo deformation to form high-surface-area ribbons that serve to inhibit dislocation movement, thus improving the mechanical properties of the molybdenum matrix. It is still unknown what specific compounds, phases, and crystal structures provide these metal-oxides with their high strength and deformability. Because the molybdate phases are formed at high temperatures and low oxygen partial pressures, little is also known of the high-temperature phase equilibria of the REO-Mo systems under these conditions. The primary goal of this study was to deifine phase equilibria on systems of Mo with rare-earth oxides. The project aimed to identify compounds, phases, and specific oxidation states of molybdenum at various processing conditions. Systems of LaO1.5-MoOx, YO1.5-MoOx, and ZrO2- MoOx were investigated at temperatures of 1000??nd 1200??and O2 partial pressures ranging from 10-4 Pa to 10-13 Pa. Samples were prepared using powder starting materials of Mo and rare-earth oxides were combined in stoichiometric ratios. The samples were then electrically heated in a ceramic tube furnace in which the oxygen partial pressure was controlled by means of a combined flow of H2 and CO2 gas. Characterization was performed using x-ray diffraction, with published powder diffraction files for phase identification.

This thesis covers the synthesis and the characterization of sodium lanthanide oxide phosphates, rare earth added strontium pyrophosphates and the Rietveld structural analysis of rare earth orthoborates. Solid state and microwave-assisted synthesis method was employed for the synthesis of desired materials. The formation of the produced phases was confirmed by X-ray Diffraction (XRD), Infrared FT-IR, Raman, Scanning Electron Microscopy (SEM) methods. By using Rietveld Refinement method, structural analysis of rare earth orthoborates were done and three dimensional crystal structures were found. In the first part of the thesis, some new sodium lanthanide oxide phosphates were synthesized by solid state reaction method from Ln2O3 (where Ln= La, Nd, Sm, Gd, Dy, Ho, Er, Yb), Na2CO3, NH4H2PO4 at 1100 oC. Na2LaOPO4, Na2NdOPO4, and Na2SmOPO4 produced with the space group is Pmm2. With the help of the same procedure new orthorhombic Na2DyOPO4, Na2HoOPO4, Na2ErOPO4, and Na2YbOPO4 were synthesized for the first time in the literature at 1100 oC with the same space group Pmm2. v In the second part of the thesis, Sr2P2O7 - ZrP2O7 solid solution was obtained by the solid state reaction and they were characterized for the first time in literature and subjected to thermoluminescence measurements showing Sr2P2O7 has glow curve around 100 oC. Then CuO and some rare earth oxides (Y2O3, La2O3, CeO2, Pr6O11, Nd2O3, Sm2O3, Eu2O3, Gd2O3, Tb2O3, Dy2O3, Ho2O3, Er2O3, Tm2O3, Yb2O3, Lu2O3) 0.5-15% (by weight) were added to pure Sr2P2O7. After structural determinations by XRD, thermoluminescence studies showed two glow peaks of Pr, Ho, and Nd along with Cu-added samples, one of them is always at around 90 oC and the other TLthermoluminescence- peak around 180, 275, and 285 oC, respectively. This study showed that rare earth added Sr2P2O7 materials can be promising material for dosimetric applications. In the third part of this work, time saving microwave-assisted synthesis method was applied to produce pure LnBO3 (Ln=La, Nd, Dy, Ho) by using urea and sucrose as a microwave active organic additive. For LaBO3 and NdBO3, space group found as Pnma and for DyBO3 and HoBO3 powders crystallized in hexagonal unit cell with P-6c2 space group. All microwave-assisted products have particle sizes lower than 1 micrometer. In the final part of this study, pure LnBO3 (Ln=Y, La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu) powder samples were produced by using solid state reactions of Ln2O3 and H3BO3 (ratio=1:2) heated at 900 oC for 10 hours and 1000 oC for 5 hours. The crystallographic studies conducted with rietveld structural refinement and unit cell parameters, background functions, profile parameters, zero shift, atomic positions, and unisotropic thermal parameters were refined. LaBO3 and NdBO3 were solved based on Pnma orthorhombic structure while the crystal structure of YBO3, DyBO3 and HoBO3 were monoclinic C2/c. SmBO3 showed triclinic P-1 structure.

Impurity trapped excitons (ITEs) occurring in divalent ytterbium doped calcium and strontium fluoride crystals have been investigated by exploiting the radically different radiative decay rates of the lowest exciton state and higher excited states, utilizing a novel two-colour transient photoluminescence enhancement experiment. The ITE energy levels have been directly measured with the observation of sharp transitions occurring from the changes of states of the localized hole and broad bands associated with changes of state of the delocalized electrons. The dynamic behaviour under excitation by time delayed ultra-violet (UV) and infrared (IR) pulses has been observed allowing for the identification of excitation and decay pathways between the ITE states. The position and transition intensities of the sharp lines within the IR excitation spectrum have been successfully matched using a semi-empirical effective Hamiltonian crystal field model. In CaCaF₂:Yb²⁺ the lines occurring at 249 and 1145 cm⁻¹ were matched with the crystal field parameter B4 = 800 cm⁻¹ and the exchange parameter G3(fs) = 5900 cm⁻¹. In SrCaF₂:Yb²⁺ these lines were observed at 178 and 1284 cm⁻¹ and matched with B4 = 600 cm⁻¹ and G3(fs) = 7278 cm⁻¹. Local heating and direct absorption by intra-excitonic transitions are found to be the causes of the broad band observed in the spectrum and have been deconvolved by studying the dynamic behaviour of the monitored emission at different IR excitation frequencies. Through this modeling, higher lying ITE states have been identified occurring at 785 cm⁻¹ in SrCaF₂:Yb²⁺ and in between 740 - 820 cm⁻¹ in CaCaF₂:Yb²⁺. The dynamic model developed successfully simulates the temporal behaviour of the emission under IR excitation under a variety of parameters including IR fluence, excitation frequency, sample temperature and UV - IR pulse delay. Examination of the SrCaF₂:Yb²⁺ dynamic behaviour over a time scale of 100 ms shows UV driven trap population at a rate of approximately 3% per pulse, which are liberated and recycled to the Yb²⁺ ground state by the IR pulse. The two-colour technique is applied to MgCaF₂:Yb²⁺, a candidate for possible ITE emission. Temperature dependent emission spectra obtained under UV excitation indicates the possibility of an ITE state, independently populated from the 5d level of the Yb²⁺. Typical 5d emission is also observed from this system. Under IR excitation, liberation of shallow traps and possible local heating is observed. No ITE emission is conclusively found with IR probing.

Thesis (Ph.D.)--McMaster University (Canada), 1990. / Source: Dissertation Abstracts International, Volume: 62-13, Section: A, page: 0000.