Biblioteca Digital

Luminescence spectroscopy of solids at 77 K has been used to characterise the uranium(VI) species incorporated into [alpha]-alumina, [gamma]-alumina and zeolites Y and ZSM-20 by adsorption from solution and into ZSM-5 by chemical synthesis. With uranyl adsorbed from nitrate solutions onto [alpha]- and [gamma]-aluminas, the luminescence measurements show the dominant uranium species is schoepite, UO3·xH2O, in agreement with results from X-ray diffraction and Raman spectroscopy. With uranyl acetate, there are indications that a crystalline acetate species is also present. With zeolite-Y and ZSM-20, the main species is a dimer. In addition, some monomeric [UO2(H2O)5]2+ is also present. With ZSM-5, although this is not observed in X-ray diffraction, the luminescence spectrum shows the presence of a species, similar to the schoepite seen with the aluminas. It is suggested that this may be due both to closely related polymeric species, and to uranyl anions, such as [UO2(OH)4]2- and [UO2(OH)3]-.; http://www.sciencedirect.com/science/article/B6TGS-435M5SD-2D/1/1fcff58939e013c8fdee4bba2d901a3b

Er and Yb co-doped ZnAl(2)O(4) phosphors were prepared by solution combustion synthesis and the identification of Er and Yb were done by energy-dispersive X-ray analysis (EDX) studies. A luminescence at 1.5 mu m, due to the (4)I(13/2) ->(4)I(15/2) transition, has been studied in the NIR region in Er and Yb co-doped ZnAl(2)O(4) phosphors upon 980 nm CW pumping. Er-doped ZnAl(2)O(4) exhibits two thermally stimulated luminescence (TSL) peaks around 174A degrees C and 483A degrees C, while Yb co-doped ZnAl(2)O(4) exhibits TSL peaks around 170A degrees C and 423A degrees C. Electron spin resonance (ESR) studies were carried out to identify defect centres responsible for TSL peaks observed in the phosphors. Room temperature ESR spectrum appears to be a superposition of two distinct centres. These centres are assigned to an O(-) ion and F(+) centre. O(-) ion appears to correlate with the 174A degrees C TSL peak and F(+) centre appears to relate with the high temperature TSL peak at 483A degrees C in ZnAl(2)O(4):Er phosphor.; Seoul R&D program (2006); Seoul R&D program (2006); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); FAPESP, Brazil

Polycrystalline Eu(2+) and Dy(3+) doped barium aluminate materials, BaAl(2)O(4):Eu(2+),Dy(3+), were prepared with solid state reactions at temperatures between 700 and 1500 degrees C. The influence of the thermal treatments on the stability, homogeneity and structure as well as to the UV-excited and persistent luminescence of the materials was investigated by X-ray powder diffraction, SEM imaging and infrared spectroscopies as well as by steady state luminescence spectroscopy and persistent luminescence decay curves, respectively. The IR spectra of the materials prepared at 250, 700, and 1500 degrees C follow the formation of BaAl(2)O(4) composition whereas the X-ray powder diffraction of compounds revealed how the hexagonal structure was obtained. The morphology of the materials at high temperatures indicated important aggregation due to sintering. The luminescence decay of the quite narrow Eu(2+) band at ca. 500 nm shows the presence of persistent luminescence after UV irradiation. The dopant (Eu(2+)) and co-clopant (Dy(3+)) concentrations affect the crystallinity and luminescence properties of the materials. (C) 2009 Elsevier B.V. All rights reserved.; CNPq Conselho Nacional de Desenvolvimento; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Cientifico e Tecnologico (CNPq); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Fundacao de Amparo A Pesquisa do Estado de Sao Paulo (FAPESP); Rede de Nanotecnologia Molecular e de Interfaces (RENAMI); Rede de Nanotecnologia Molecular e de Interfaces (RENAMI); Instituto do Milenio de Materiais Complexos (IM²C); Instituto do Milenio de Materiais Complexos (IM²C); Graduate School of Materials Research (GSMR...

Dosimetria usando Luminescência Opticamente Estimulada (OSL) é uma área em constante crescimento dentro da ciência e com excelentes perspectivas comerciais. O Óxido de Alumínio crescido na presença de uma atmosfera rica em Carbono (Al 2O3:C) tem fornecido bons resultados como detector luminescente. Esse material apresenta alta sensibilidade à radiação ionizante e boa resposta à estímulos ópticos. Estima-se que cerca de dois milhões de pessoas façam uso de dosímetros com detectores de Al 2O3:C em rotinas de dosimetria individual externa, que por apresentar varias vantagens experimentais acredita-se substituirá as outras duas técnicas dosimétricas mais adotadas: dosimetria fotográfica e termoluminescente. A certificação de uma técnica de dosimetria para uso comercial exige uma série de estudos. Neste trabalho apresentamos contribuições que complementam o entendimento e adoção da técnica de OSL em dosimetria pessoal. Nossa primeira contribuição consiste numa serie de testes de desempenho mostrando a eficácia da técnica para justificar nossa proposta de certificação de dosimetria individual externa usando OSL no Brasil. No intuito de relacionar centros paramagnéticos e o processo de luminescência, apresentamos resultados de espectros de EPR em detectores OSL. Detectamos e classificamos sinais de EPR relacionados a impurezas nas amostras...

Nesta dissertação, visamos o entendimento de processos intermediários que regem a transferência de energia e determinam as propriedades ópticas de polímeros conjugados, a fim de encontrar meios para aumentar a eficiência de emissão e o tempo de vida dos ?LED?s? orgânicos. Estudamos especificamente o polímero PPV, poli(p-fenileno vinilideno), sintetizado através de novo método desenvolvido no Grupo de Polímeros do Instituto de Física de São Carlos, por Marletta e colaboradores[1], na forma de filmes finos depositados pelas técnicas ?spincast? e de automontagem (LbL). Para o trabalho utilizamos técnicas espectroscópicas de luminescência, excitação seletiva e absorbância. Por meio de técnicas de engenharia molecular e através do ordenamento induzido da rede polimérica, avaliamos o peso que têm os eventos intermediários à emissão. Estiramos gradualmente filmes de PTHT/PPV depositados sobre Teflon, sob um eixo preferencial, e constatamos a dependência da polarização da luz emitida com processos de transferência de energia e com a anisotropia da matriz polimérica. Realizamos a separação das cadeias do copolímero a fim de analisar separadamente a transferência de energia entre os segmentos conjugados pertencentes a cadeias distintas (processos intercadeia) ou ao longo da cadeia (processos intracadeia). Esta separação intercadeia e intracadeia resultaram em um significativo aumento da eficiência da emissão...

Materiais com luminescência persistente são normalmente baseados em aluminatos e silicatos dopados com íons Eu2+, portanto buscam-se novos materiais com diferentes dopantes. Consequentemente, os materiais BaAl2O4:Eu2+,TR3+ (R: La-Lu) foram preparados pelo método de combustão com temperaturas de ignição entre 400 e 600 °C, assim como pelo método cerâmico a 1500 °C. Os sistemas mais versáteis CdSiO3:TR3+ foram preparados apenas pelo método cerâmico a 950 °C. Para estudar a estrutura e a pureza de fase dos materiais utilizou-se espectroscopia de absorção no infravermelho, difração de raios X (método do pó) e microscopia eletrônica de varredura. Os estados de oxidação e o ambiente ao redor dos íons terras raras foram investigados com a espectroscopia de absorção de raios X com radiação Síncrotron (XANES e EXAFS). As propriedades da luminescência persistente dos fósforos foram investigadas com as técnicas de termoluminescência (TL), fotoluminescência e espectroscopia com radiação Síncrotron na região do UV-UV vácuo. Baseado nas medidas de TL, a estrutura dos defeitos dos materiais BaAl2O4:Eu2+,TR3+ (TR: Nd e Dy) e CdSiO3:TR3+ (TR: Pr, Gd e Tb) mostrou-se ideal para a luminescência persistente a temperatura ambiente. Os espectros de XANES indicaram a presença dos estados divalente e trivalente do Eu dopado na matriz BaAl2O4...

O abafamento da luminescência em materiais contendo impureza de ferro é um fenômeno que ainda merece ser cuidadosamente investigado para que se possa chegar a uma descrição detalhada dos processos envolvidos. A matriz hospedeira escolhida para a realização deste trabalho foi o vidro 20 Al IND 2 o IND 3 ; 50 B IND 2 o IND 3 ; 30 BaO (mol%), do qual foram preparadas amostras às quais foram adicionadas quantidades variando de 10 POT -3 a 0,8 at% de Fe. A razão desta escolha prende-se ao fato de que a cinética de recombinação entre o centro de elétron do boro (BEC) e o centro de lacuna do boro e oxigênio (BOHC) em vidros boratos irradiados com raio-X a 77 K, responsável por uma intensa luminescência azul, já se conhece em detalhe através de resultados recentes de ressonância paramagnética eletrônica (RPE). A partir destes dados foi identificado cada um dos centros envolvidos na reação e foi possível acompanhar detalhadamente a cinética dos respectivos decaimentos térmicos. Com o apoio destas informações, os dados de termoluminescência (TL) deste trabalho puderam ser interpretados com maior segurança. Um arranjo experimental foi especialmente construído para a realização de medidas de TL na faixa de temperaturas entre 77 e 300 K. As medidas mostraram uma queda exponencial da TL em função da concentração de Fe. A supressão total da luminescência foi obtida para amostras contendo -0...

The luminescence properties of solid hydrated lanthanide squarates (Ln2(C4O4)3(H2O) x; x = 8 or 13;Ln3+ = Gd, La, Eu, Tb, Pr) are reported for temperatures down to 4.2K. The luminescence of the squarate group is observed for the Gd3+ and La3+ compounds at low temperatures (below 150K). The Pr3+ compound does not show any emission at all, not even at 4.2K. This is ascribed to the quenching of the Pr3+ emission by multiphonon relaxation and/or concentration quenching. The quantum efficiencies of the 5D0 emission of Eu3+ and of the 5D4 emission of Tb3+ in these squarate complexes are strikingly different. Whereas the Tb3+ emission shows a temperature independent quantum efficiency of 50% upon ligand excitation, the Eu3+ emission is strongly quenched, showing a temperature dependent quantum efficiency of 0.8% at 4.2K upon ligand excitation. This quenching is ascribed to the low energy position of the charge-transfer state of Eu3+ in these compounds.

Pós-graduação em Química - IQ; Les travaux présentés dans ce manuscrit concernent l’étude de nouvelles vitrocéramiques transparentes à base de chalco-halogénures dopées par des ions de terres pour la luminescence dans le visible. L’addition de différents halogénures d’alcalins à des verres du système Ga2S3-GeS2 a été étudiée avec l’objectif d’étendre leur transparence vers l’ultraviolet. Des verres du système Ga2S3- GeS2-CsCl complètement transparents dans le visible (400-750 nm) jusqu’au moyen infrarouge (11,5 μm) ont été obtenus. Des vitrocéramiques transparentes et homogènes ont ensuite été préparées de manière contrôlée à partir de plusieurs verres à différentes teneurs en CsCl dans le système Ga2S3-GeS2-CsCl. Des nanocristallites de taille homogène et uniformément dispersées dans la matrice amorphe sont formées de manière reproductible par des traitements thermiques appropriés. Une étude d’un point de vue structural de la cristallisation a été réalisée par diffraction de rayons X et résonance magnétique nucléaire à l’état solide sur les noyaux 71Ga et 133Cs. Le rôle d’agent de nucléation du gallium a été mis en évidence dans cette matrice avec la cristallisation d’une phase Ga2S3. Un meilleur comportement mécanique a également été observé pour les matériaux composites préparés. Des vitrocéramiques dopées par des ions de terres rares (praséodyme Pr3+ et néodyme Nd3+) ont été synthétisées dans le système Ga2S3-GeS2-CsCl. L’évolution de la luminescence dans le visible des ions Pr3+ et Nd3+ a été étudiée en fonction des conditions de traitement thermique. Au vu des résultats obtenus...

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Processo FAPESP: 12/21450-1; Solid-state compounds of the general formulae [ML3] (M = Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y; L = ketoprofen) were synthesized and characterized using infrared, diffuse reflectance and luminescence spectroscopies. IR data suggested that the carboxylate group in ketoprofen is coordinated to the metals as a bidentate ligand. The triplet state energy level was determined using the Gd3+ complex, which exhibited a ketoprofen blue luminescence when excited in the UV region. The compound containing Tb3+ ion was sensitized by the ligand and emitted in the green region of the visible spectrum. On the other hand, for the analogous species containing the dysprosium ion, a competition for luminescence between the Dy3+ and the ligand levels was observed. Finally, Tm3+ complex exhibits only ligand luminescence. These optical behaviors are discussed based on rare earth energy diagrams. In addition, the compounds were evaluated for their anti-inflammatory activities. All the compounds showed a higher production of H2O2 and IL-10 than the ketoprofen...

O uso de radiação ionizante é cada vez mais intenso, seja na indústria seja na área médica. Os efeitos nocivos da radiação ionizante exigem medidas de segurança na sua utilização e um dos meios mais comuns para proteção da saúde do operador de equipamentos que usam esta radiação é o controle da dose que este pode receber em determinado período de tempo. Para tal controle, são normalmente utilizados dosímetros pessoais. Estudos sobre datação de sedimentos costeiros e fluviais do Brasil têm encontrado tipos específicos de quartzo com excelentes características dosimétricas. Com o objetivo de analisar as propriedades dosimétricas de amostras de quartzo de elevada sensibilidade de luminescência e avaliar a sua possível utilização na dosimetria pessoal, foram feitos testes comparativos com amostra do principal e mais utilizado dosímetro pessoal do tipo OSL (Optically Stimulated Luminescence), o Al2O3:C. Este trabalho apresenta as características de luminescência de amostras de quartzo. Essas características foram determinadas por testes de recuperação de dose conhecida (dose recovery) por meio de protocolo de alíquota única (Single-Aliquot Regenerative ¿ SAR) em amostras irradiadas por fonte de radiação beta. Foram realizados testes de sensibilidade e de estabilidade do sinal OSL e testes com radiação gama. Os resultados mostraram que as amostras de quartzo estudadas foram capazes de recuperar com exatidão doses de 50 mGy a 50Gy. Estimou-se que as amostras de quartzo saturam em doses (114-175 Gy) superiores à dose de saturação da amostra de Al2O3:C (35 Gy). A dose mínima capaz de ser medida pelas amostras de quartzo variou de 0...

A suite of fluvial terraces (T1–T6,from top to bottom of the staircase) occur along a _70km stretch of the Tejo River in central Portugal, between the small towns of Gavião and Chamusca. Terrace correlation was based upon the following: (a)aerialphotograph analysis, geomorphological mapping and field topographic survey; (b) sedimentology of the terrace deposits, namely the maximum particle size, clast composition and lithofacies identification; and (c) K-feldspar infrared stimulated luminescence (IRSL) dating of the three lower terraces levels, as quartz optically stimulated (OSL) signal of the samples from these terraces was too close to saturation for all but two samples.The two upper terraces (T1andT2) lack suitable materials for luminescence dating (e.g.sands/silts),but also their probable ages are beyondthe upper range of the dating method. Fault saffecting terraces and older deposits have been reported. The luminescence dating results suggest that some assignments of local terrace remnants were in correct because of fault-related vertical displacements. The luminescence dating procedure also included a correction for anomalous fading in order to obtain more reliable estimates of the burial ages. The fading rate was identical for all samples...

Upconversion nanocrystals convert infrared radiation to visible luminescence, and are promising for applications in biodetection, bioimaging, solar cells and three-dimensional display technologies. Although the design of suitable nanocrystals has improved the performance of upconversion nanocrystals, their emission brightness is limited by the low doping concentration of activator ions needed to avoid the luminescence quenching that occurs at high concentrations. Here, we demonstrate that high excitation irradiance can alleviate concentration quenching in upconversion luminescence when combined with higher activator concentration, which can be increased from 0.5 mol% to 8 mol% Tm(3+) in NaYF₄. This leads to significantly enhanced luminescence signals, by up to a factor of 70. By using such bright nanocrystals, we demonstrate remote tracking of a single nanocrystal with a microstructured optical-fibre dip sensor. This represents a sensitivity improvement of three orders of magnitude over benchmark nanocrystals such as quantum dots.; Jiangbo Zhao, Dayong Jin, Erik P. Schartner, Yiqing Lu, Yujia Liu, Andrei V. Zvyagin, Lixin Zhang, Judith M. Dawes, Peng Xi, James A. Piper, Ewa M. Goldys and Tanya M. Monro

Applications of luminescence dating to Quaternary earth science are reviewed, the examples being from Australia. The methods of thermoluminescence (TL) and optical dating using optically stimulated luminescence (OSL) are briefly described, together with their limitations. Prominent results are: (i) the distribution of ages of Australian desert dunes shows peak activity at about the time of the last glacial maximum; (ii) the lake-full episodes of Lake Eyre are traced back to 140 ka; (iii) the ages of relict beach dunes in South Australia, when compared with independent geological ages based on δ18O records, show that luminescence dating can be used for ages to 500 ka and older; and (iv) the development of interior river systems has been traced. Among less common applications are: (i) the dating of Australia's youngest volcanoes at 5-4 ka (in these cases the luminescence signal was reset by heat); (ii) the determination of age vs depth of a deep-sea core; and (iv) the age of earthquakes (from the age of the infilling of fault scarps). The emphasis is on recent work and is illustrative rather than exhaustive, the object being to show the scope of luminescence dating. There are suggestions where further research might be directed.; J. R. Prescott and G. B. Robertson

Ce travail est axé vers la compréhension détaillée des propriétés de luminescence de composés de certains métaux lourds. La première partie de ce mémoire décrit la caractérisation spectroscopique d'un radical de type nitronyle nitroxyde, 2-(2-pyridinyl)-4,4,5,5-tétraméthyl-4,5-dihydro-1H-imidazolyl-1-oxyl-3-oxyde, abrégé (NIT2-Py), et de ses complexes avec les cations Tb(III), [Tb(hfac)3NIT2-Py], et Y(III), [Y(hfac)3NIT2-Py]. La variation de la température affecte les spectres de luminescence qui montrent de la structure vibronique résolue. Les maxima de ces transitions vibroniques se rapprochent au fur et à mesure que la température augmente. Ces variations des maxima en fonction de la température ne correspondent pas à des variations de fréquences vibrationnelles et sont de l'ordre de 200 cm-1 entre 80 K et 240 K. La variation de la température n'a pas d'influence significative sur la structure moléculaire, comme atteste la variation mineure des maxima des spectres Raman entre 80 K et 300 K. La comparaison des spectres expérimentaux à des spectres calculés montre que ces variations peuvent être reproduites par l'utilisation d'une combinaison de fréquences vibrationnelles. Le paramètre dont la variation est très significative est la résolution du spectre de luminescence...

In this paper, the covalent immobilization and luminescence enhancement of a europium (Eu(III)) complex in a porous silicon (pSi) layer with a microcavity (pSiMC) structure are demonstrated. The alkyne-pendant arm of the Eu(III) complex was covalently immobilized on the azide-modified surface via ligand-assisted "click" chemistry. The design parameters of the microcavity were optimized to obtain an efficient luminescence-enhancing device. Luminescence enhancements by a factor of 9.5 and 3.0 were observed for Eu(III) complex bound inside the pSiMC as compared to a single layer and Bragg reflector of identical thickness, respectively, confirming the increased interaction between the immobilized molecules and the electric field in the spacer of the microcavity. When comparing pSiMCs with different resonance wavelength position, luminescence was enhanced when the resonance wavelength overlapped with the maximum emission wavelength of the Eu(III) complex at 614 nm, allowing for effective coupling between the confined light and the emitting molecules. The pSiMC also improved the spectral color purity of the Eu(III) complex luminescence. The ability of a pSiMC to act as an efficient Eu(III) luminescence enhancer, combined with the resulting sharp linelike emission...

Blue luminescence from TaZZn30g and green luminescence from Mn doped TaZZn30g has been observed under low voltage cathodoluminescent excitation, In this article , the luminescence mechanisms of TaZZn30g and Mn doped TaZZn30 g are discussed in detail. The results suggest that the intrinsic blue luminescence of TaZZn30g results from a metal-to-ligand transition, whereas the green luminescence of Mn doped TaZZn30g results from the Mn 4T 1-6A I transition. The suppression of the blue intrinsic luminescence in Mn doped TaZZn30g suggests that efficient energy transfer from the host material to the Mn occurs. This energy transfer phenomenon is also discussed by comparing the photoluminescence excitation spectra of both thin film materials. Finally, the relative efficiency versus voltage and current density is demonstrated and discussed pertaining to field emission device operation.; Journal of Applied Physics article. Please see www.aip.org for more information.

We have studied the temperature dependence of the luminescence of ion implanted GaAs between 10 and 300 K. We found that at certain temperatures the luminescence increases with increasing temperature. We attribute these localised increases in the luminescence intensity to the thermal excitation of carriers out of traps, or in other words, to thermally stimulated luminescence or thermoluminescence. Model calculations which include thermoluminescence produce excellent agreement with the experimental data and allow us to determine the trap parameters.

The loess-paleosol sequences in New Zealand are among the thickest in the southern hemisphere, and preserve an important terrestrial record of paleoclimatic changes. Unlike loess-paleosol sequences in North Island, most of those in South Island lack discrete chronostratigraphic marker ash beds, excepting perhaps the widespread ∼24 ka Kawakawa Tephra. Therefore, any specific correlation to marine isotope stage (MIS) proxy records or to loess-paleosol sequences in the northern hemisphere has been unknown. Hence, we applied luminescence sediment dating to four key loess-paleosol sequences from southern South Island. Although these pioneering results suggest that further sampling and luminescence dating are needed, they do provide: (1) the first numeric age constraint (44±3ka on overlying loess) for the end of deposition of the geomorphically and paleoclimatically important Edendale Terrace gravels; (2) the first numeric evidence that the youngest loess-paleosol unit (L1) at the near-coastal Romahapa and inland Stewarts Claim sites began to be preserved much earlier (at ∼60 ka) than at the inland Kingston Crossing site (∼35 ka); (3) the first direct evidence that the 6 m Romahapa sequence extends at least to ∼350 ka, the oldest yet TL-dated such sequence in South Island. Furthermore...

Luminescence measurements are extremely sensitive to variations in structural environment and thus have the potential to probe distortions of fluorescence sites. Changes can be monitored via luminescence efficiency, emission spectra or excited state lifetimes and these factors are influenced by the local neighbourhood around the emission site, and therefore by structure, composition, pressure and temperature. A rarely exploited approach for condensed matter has been to use the changes in luminescence responses during heating or cooling of a material to provide a rapid survey to detect the presence of phase transitions. One can often differentiate between bulk and surface effects by contrasting results from radioluminescence for bulk responses, and cathodoluminescence or photoluminescence for surface effects. One expects that discontinuous changes in optical parameters occur during temperature changes through phase transitions of insulating materials. In practice, optical signals also exist from surface states of fullerenes and high temperature superconductors etc which identify the presence of structural or superconducting transitions. Numerous examples are cited which match standard documented transitions. Interestingly, many examples show the host signals are strongly sensitive to impurity phase transitions from inclusions such as nanoparticles of water...