• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 32
  • 15
  • 14
  • 3
  • 3
  • 1
  • Tagged with
  • 71
  • 71
  • 27
  • 23
  • 22
  • 22
  • 12
  • 12
  • 11
  • 11
  • 10
  • 10
  • 9
  • 9
  • 9
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Etude des mécanismes de coloration de verres obtenue par échange ionique Ag+/Na+ et précipitation de nano agrégats métalliques / Study of the mechanisms of glasses-colouring obtained by Ag+/Na+ ionic exchange and formation of metallic nanoparticles

Veron, Olivier 13 December 2010 (has links)
L’objectif est d’étudier par la méthode d’échange ionique à l’argent de verres silicatés la coloration induite etla réalisation de guides d’ondes planaires. Deux méthodes de modélisation de l’échange ionique sont présentées pour évaluer les paramètres de l’échange qui sont le coefficient de diffusion, la forme du profil et la mobilité des ions. Cette technique purement thermique permet la réalisation de guides d’onde à gradient d’indice, l’ajout d’un champ électrique permet d’obtenir un profil à saut d’indice. Différentes compositions de verre sont étudiées dans le but de déterminer la variation d’indice induite par la polarisabilité de l’ion argent plus forte que les ions sodium ou lithium initialement présents dans les verres. A la suite de l’échange ionique, un recuit peut être effectué dans le but de précipiter l’argent en nanoparticules métalliques qui possèdent des propriétés d’absorption intéressantes permettant de colorer les verres : la résonance plasmon de surface (RPS). Le mécanisme de formation de ces nanoparticules dépend de la température et de l’effet redox de l’environnement. L’irradiation effectuée par un laser pulsé nanoseconde des verres échangés permet la précipitation locale des nanoagrégats d’argent à la surface des verres. L’irradiation pulsée en régime femtoseconde permet une interaction dans le volume du verre, soit avec des nanoparticules déjà présentes dans le but de modifier la couleur localement, soit avec des verres échangés dans lequel des défauts sont générés pour ensuite favoriser la formation de nanoparticules par recuit. La modélisation de la résonance plasmon de surface effectuée permet d’évaluer le mécanisme de croissance des nanoparticules dans les verres. Les méthodes de caractérisation utilisées sont la microscopie électronique à balayage, la microscopie électronique en transmission, la spectrophotométrie UV/Visible, la photoluminescence et la spectroscopie infrarouge à transformée de Fourier. / The main purpose is to study by the method of silver ionic exchange of silicate glasses the induced coloring and the realization of planar waveguides.Two methods of modelization of Ionic exchange are presented to estimate the exchange parameters which are diffusion coefficient, profile’s shape and ions mobility. This purely thermal method allows the realization of graded index waveguide, the addition of an electric field allows to obtain a step index profile. Various glass compositions are studied with the aim of determining the index variation induced by a polarizability of silver ions stronger than those of sodium/lithium ions initially contained in glasses. Following the Ionic exchange, an annealing can be made with the aim of precipitating silver in metallic nanoparticles which possess interesting properties of absorption allowing to color glasses : the Surface Plasmon Resonance (SPR). The nanoparticles formation mechanism depends on temperature and on redox effect of the medium. The irradiation made with a pulsed laser in nanosecond regime of exchanged glasses allows the local formation of silver nanoaggregates onto the glass surface. The pulsed irradiation in femtosecond regime allows an interaction into the glass volume, either with already present nanoparticles with the aim of modifying the color locally, or with exchanged glasses in which the defects are generated to favor then the formation of nanoparticles by annealing. The modelization of Surface Plasmon Resonance allows the evaluation of the nanoparticles growth mechanism in glasses. The used methods of characterization are Scanning Electron microscopy, Transmission Electron Microscopy, UV/Visible Spectroscopy, Photoluminescence and Fourier Transform Infrared Spectroscopy.
2

Metallic nanoparticles: analytical properties of the acoustic vibrations and applications

Wu, Jian 16 August 2017 (has links)
This thesis focuses on the analytical properties of the acoustic vibrations and applications of metallic nanoparticles. With regard to the analytical properties of the acoustic vibrations, we focus on nanoparticle acoustic resonance enhanced four-wave mixing (FWM) as an in situ characterization technique for characterizing nanoparticles’ shape, size, and size distribution. The nonlinear optical response of metallic nanoparticles is resonantly driven by the electrostriction force which couples to the acoustic vibrations of nanoparticles. Information about nanoparticles’ shape, size, and size distribution can be obtained by analyzing the resonant peak position and linewidth in the FWM signal which carries the information about the vibrational modes. We characterize different nanoparticle solutions of different materials, shapes, and sizes using this FWM technique. Information obtained from the FWM characterization agrees well with the scanning electron microscopic examination, indicating the FWM technique can serve as an in situ nanoparticle characterization tool. We also demonstrate the FWM technique can be used for monitoring nanoparticle growth in situ. iii With regard to the applications of metallic nanoparticles, we focus on quantification of an exogenous cancer biomarker Acetyl Amantadine using surface-enhanced Raman scattering (SERS). Raman spectroscopy can provide unique fingerprint information of molecules, which can be used as a chemical detection and identification technique. The intrinsically weak Raman signal caused by the small scattering cross section presents a barrier for trace chemical detection. Localized surface plasmon resonance of metallic nanoparticles can provide large local field enhancement, which can be utilized to enhance the intrinsically weak Raman signal. In order to achieve higher local field enhancement, we focus on using the gap structures formed between nanoparticles instead of using discrete nanoparticles. Molecules should locate within the hot spots of the gap structures to experience the largest enhancement. This requires that molecules should be extracted from volume onto the metallic surface. Based on these guidelines, two SERS platforms are designed using gold nanoparticles (nanorods and nanospheres) combined with different surface functionalization techniques. The performance of these two platforms are characterized by investigating the sensitivity and limit of detection (LOD). 16 ng/mL and 0.4 ng/mL LODs are achieved for nanorod and nanosphere platforms, respectively. / Graduate
3

Nanoscale Temperature Measurement of Phase Transition in Water Using Novel Optical Thermometry Techniques

Alaulamie, Arwa A. 14 September 2017 (has links)
No description available.
4

Effects of Metallic Nanoalloys on Dye Fluorescence

Dorcéna, Cassandre Jenny 15 October 2007 (has links)
Metallic nanoparticles (NPs) are exploited for their ability to interact with organic compounds and to increase significantly the fluorescence intensity and the photostability of many fluorescent dye molecules. Metal enhanced fluorescence (MEF) is therefore widely investigated for biosensing applications. When used in immunoassays, silver island films (SIFs) could augment the fluorescence intensity of fluorescein by a factor of seventeen; SIFs were also able to double or triple the emission intensity of cyanine dyes which are commonly used in (deoxyribonucleic acid) DNA microarrays. The emission intensity of indocyanine green — widely used as a contrast agent in medical imaging — was about twenty times higher in the proximity of SIFs. This enhancement phenomenon — due to the surface plasmon polaritons associated with the metallic NPs — can be explained by energy transfer from the metal NPs to the fluorescent dye molecules or by a modified local electromagnetic field experienced by the fluorophores in the vicinity of metal surfaces. Our research focused on the optical characterization of colloidal gold-silver alloy NPs containing different ratios of gold and silver (Au<sub>1.00</sub>-Ag<sub>0.00</sub>, Au<sub>0.75</sub>-Ag<sub>0.25</sub>, Au<sub>0.50</sub>-Ag<sub>0.50</sub>, and Au<sub>0.25</sub>-Ag<sub>0.75</sub>), as well as their interaction with three fluorophores: rose bengal, rhodamine B, and fluorescein sodium. Depending upon the dye quantum yield and its concentration in solution, enhancement or quenching of fluorescence was obtained. Thus, a three to five times increase in fluorescence intensity was observed in a 2.0 mM solution of rose bengal with all nanoalloys, a slight enhancement of fluorescence (1.2 – 1.6 times) was noticed in a 0.13 mM solution of rhodamine B with all four types of NPs, and fluorescence quenching occurred in all the fluorescein-NP solutions regardless of the dye concentration. / Master of Science
5

Defects and deformation in nanostructured metals

Carlton, Christopher Earl 29 June 2010 (has links)
A better understanding of how the nanoscale environment affects the mechanical properties of materials, in particular metallic nanoparticles and nanocrystalline metals is vital to the development of next generation materials. Of special interest is obtaining a fundamental understanding of the inverse Hall-Petch Effect in nanocrystalline metals, and nanoindentation in individual nanoparticles. Understanding these subjects is critical to understanding how the mechanical properties of materials are fundamentally affected by nanoscale dimensions. These topics have been addressed by a combination of theoretical modeling and in-situ nanoindentation transmission electron microscopy (TEM) analysis. Specifically, the study of the inverse Hall-Petch effect in nanocrystalline metals will be investigated by a thorough review of the literature followed by a proposed novel theoretical model that better explains the experimentally observed behavior of nanocrystalline metals. On the other hand, the nanoindentation of individual nanoparticles is a very new research topic that has yet to aggregate a large body of experimental data. In this context, in-situ TEM nanoindentation experiments on silver nanoparticles will be first performed to determine the mechanisms of deformation in these nanostructures. A theoretical explanation for the observed deformation mechanisms will be then developed and its implications will be discussed. In addition to nanoparticles, this study will also provide unique and valuable insight into the deformation mechanisms of nanopillars, a growing area of research despite much controversy and speculation about their actual mechanisms of deformation. After studying the novel behavior of both nanocrystalline metals and nanoparticles, useful applications of both classes of materials will be explored. The discussion of applications will focus on utilizing the interesting behaviors explored in the dissertation. Of particular interest will be applications of nanoparticles and nanocrystalline materials to coatings, radiation resistance and super-plastic materials. / text
6

GRAPHENE-BASED SEMICONDUCTOR AND METALLIC NANOSTRUCTURED MATERIALS

Zedan, Abdallah 12 April 2013 (has links)
Exciting periods of scientific research are often associated with discoveries of novel materials. Such period was brought about by the successful preparation of graphene which is a 2D allotrope of carbon with remarkable electronic, optical and mechanical properties. Functional graphene-based nanocomposites have great promise for applications in various fields such as energy conversion, opteoelectronics, solar cells, sensing, catalysis and biomedicine. Herein, microwave and laser-assisted synthetic approaches were developed for decorating graphene with various semiconductor, metallic or magnetic nanostructures of controlled size and shape. We developed a scalable microwave irradiation method for the synthesis of graphene decorated with CdSe nanocrystals of controlled size, shape and crystalline structure. The efficient quenching of photoluminescence from the CdSe nanocrystals by graphene has been explored. The results provide a new approach for exploring the size-tunable optical properties of CdSe nanocrystals supported on graphene which could have important implications for energy conversion applications. We also extended this approach to the synthesis of Au-ceria-graphene nanocomposites. The synthesis is facilely conducted at mild conditions using ethylenediamine as a solvent. Results reveal significant CO conversion percentages between 60-70% at ambient temperatures. Au nanostructures have received significant attention because of the feasibility to tune their optical properties by changing size or shape. The coupling of the photothermal effects of these Au nanostructures of controlled size and shape with GO nanosheets dispersed in water is demonstrated. Our results indicate that the enhanced photothermal energy conversion of the Au-GO suspensions could to lead to a remarkable increase in the heating efficiency of the laser-induced melting and size reduction of Au nanostructures. The Au-graphene nanocomposites are potential materials for photothermolysis, thermochemical and thermomechanical applications. We developed a facile method for decorating graphene with magnetite nanocrystals of various shapes (namely, spheres, cubes and prisms) by the microwave-assisted-reduction of iron acetylacetonate in benzyl ether. The shape control was achieved by tuning the mole ratio between the oleic acid and the oleyamine. The structural, morphological and physical properties of graphene-based nanocomposites described herein were studied using standard characterization tools such as TEM, SEM, UV-Vis and PL spectroscopy, powder X-ray diffraction, XPS and Raman spectroscopy.
7

Síntese e caracterização de vidros de telureto dopados com íons de Eu3+ e Tb3+ com nanopartículas metálicas. / Synthesis and characterization of tellurite glasses doped with Eu3+ and Tb3+ ions with metallic nanoparticles.

Pinto, Ricardo de Almeida 31 March 2009 (has links)
Neste trabalho são apresentadas a síntese e caracterização das propriedades luminescentes dos sistemas vítreos TeO2-ZnO e TeO2-ZnO-PbO-Na2O dopados com íons de európio e térbio contendo nanopartículas (NPs) metálicas de prata, ouro e cobre, para aplicações em dispositivos fotônicos. Estes vidros possuem uma larga região de transmissão (350-6500 nm), elevada estabilidade química, resistências mecânica e térmica, baixa energia de fônon (em torno de 700 cm-1) e alto índice de refração (~ 2,0). Por meio de medidas de absorção óptica foi observada a incorporação dos íons de terras-raras na forma trivalente, responsável pelo fenômeno de luminescência nos vidros e a presença de bandas de absorção relacionadas à ressonância dos plasmons superficiais (RPS), localizadas em aproximadamente 490 nm (no caso das NPs de prata), em 500 nm (no caso das NPs de ouro) e em torno de 800 nm (no caso das NPs de cobre). A caracterização das NPs metálicas foi realizada por meio da Microscopia Eletrônica de transmissão auxiliada pelas técnicas de difração de elétrons e espectrometria de energia dispersiva (EDS) e permitiu a observação de NPs metálicas, cristalinas e de diversos formatos e tamanhos. As medidas de emissão foram realizadas excitando as amostras em 405 nm para as dopadas com Eu3+ e 377 nm para as amostras dopadas com Tb3+, por meio de um espectrômetro de fluorescência, com lâmpada de Xenon de pulsos de 2 a 3 s. Foram medidas bandas de emissão associadas à emissão do Eu3+ em 580 nm, 590 nm, 614 nm, 650 nm e 695 nm devidas às transições 5D07FJ (com J = 0 até 4). A banda situada em 614 nm, associada a uma transição de dipolo-elétrico é a mais intensa, por ser mais sensível às mudanças do campo local provocado pela presença das NPs metálicas. Para as amostras dopadas com Tb3+ foram observadas emissões em 485 nm, 550 nm, 590 nm e 623 nm, associadas às transições 5D47FJ (com J = 6 até 3), sendo a emissão em 550 nm associada também a uma transição de dipolo-elétrico e portanto a mais sensível às alterações do campo local provocado pela presença das NPs metálicas. Para as amostras codopadas com íons de Eu3+ e Tb3+, foram observados aumentos significativos da luminescência referente à emissão em 614 nm na presença de NPs de prata. A obtenção de aumento da luminescência dos íons de Eu3+ somente pela transferência de energia proveniente do Tb3+ não é um mecanismo trivial. Entretanto, foi observado em amostras preparadas com diferentes concentrações de íons aceitadores e doadores e intensificada também na presença de NPs de prata. Os aumentos ocorridos na luminescência são provavelmente causados pelo aumento do campo local nas proximidades dos íons de terras-raras e por processos de transferência entre as NPs metálicas e os íons de terras-raras. Nestes casos a distância entre os íons de terras-raras e as NPs está compreendida entre 5 nm e 20 nm. Portanto, a presença das NP desempenha um papel importante para o aumento da luminescência, permitindo o desenvolvimento de novos materiais com aplicações em nanofotônica. / This work presents the synthesis and characterization of luminescent properties of vitreous systems TeO2-ZnO e TeO2-ZnO-PbO-Na2O doped with ions of europium and terbium containing silver, gold and copper nanoparticles (NPs), for applications in photonic devices. These glasses have a large window transmission (350-6500 nm), chemical stability, mechanical and thermal resistance, low phonon energy (around 700 cm-1) and high refraction index (~2,0). The optical absorption measurement showed the incorporation of rareearths ions in the trivalent form, responsible for the luminescence phenomenon in the glasses and the presence of absorption bands related to the surface plasmons resonance (SPR), located in approximately 490 nm (in the case of silver NPs) in 500 nm (in the case of gold NPs) and around 800 nm (in the case of copper NPs). The characterization of the metallic NPs was perfomed with transmission electron microscopy (TEM) with the aid of electron diffraction and energy dispersive spectroscopy techniques that allowed the observation of metallic NPs, crystalline with several shapes and sizes. The measurements were made through with excitation of 405 nm for samples doped with Eu3+ and 377 nm for samples doped with Tb3+, using a fluorescence spectrometer, with Xenon lamp with pulses varying from 2 to 3 s. The bands associated to Eu3+ emission were measured at 580 nm, 590 nm, 614 nm, 650 nm and 695 nm due to the transitions 5D07FJ (with J = 0 to 4). The band situated at 614 nm related to electric dipole transition is the most intense because it is sensitive to changes in the local field, caused by the presence of metallic NPs. For samples doped with Tb3+ it was observed emissions at 485 nm, 550 nm, 590 nm and 623 nm, associated with the transitions 5D47FJ (with J = 6 to 3) being the 550 nm emission also related to electric dipole transition and consequently the most sensitive to changes in the local field, caused by the presence of metallic NPs. For the samples codoped with Eu3+ and Tb3+ ions it was observed significative enhancement of the luminescence at 614 nm emission in the presence of silver NPs. The achievement of the enhancement of the luminescence of Eu3+ ions only by energy transfer from Tb3+ is not a trivial mechanism. However, it was observed in samples prepared with different concentrations of acceptor and donors ions and intensified in the presence of NPs silver. The enhancement of the luminescence is probably caused by the increase of the local field around the rare earth ions and by processes of energy transfer between the metallic NPs and the rare earth ions. In these cases the distance between the rare earth ions and the metallic NPs ranges from 5 to 20 nm. Thus, the presence of metallic NPs plays an important role for the enhancement of the luminescence, allowing the development of new materials with application in photonic.
8

Produção e caracterização de guias de ondas de germanato codopados com Er3+ e Yb3+ contendo nanopartículas metálicas para aplicações ópticas no infravermelho. / Production and characterization of Er3+ and Yb3+ codoped germate waveguide with metallic nanoparticles for infrared optical applications.

Bomfim Júnior, Francisco Araújo 29 June 2016 (has links)
O presente trabalho apresenta a produção e a investigação das propriedades ópticas de guias de onda vítreos baseados no sistema PbO-GeO2, codopados com íons de érbio de itérbio e contendo nanopartículas metálicas de ouro e prata, para aplicações como dispositivos fotônicos na terceira janela de telecomunicações (1530 nm). Os guias de onda foram obtidos por meio de processos convencionais utilizados em microeletrônica usando a técnica RF Magnetron Sputtering para deposição do material sobre uma estrutura do tipo PEDESTAL. Os primeiros guias produzidos apresentaram irregularidades laterais próximas ao núcleo que contribuíram para o aumento das perdas. Mudanças no processo de fabricação como a diminuição da espessura da máscara de cromo usada para a corrosão do SiO2, etapa adicional para a corrosão e a diminuição da espessura do guia de onda proporcionaram redução das perdas por propagação e aumento do ganho óptico em ~50% estimado em 6,0 dB/cm, em 1530 nm, para um guia de onda de 80 µm de largura. Entretanto, as dificuldades para medir guias com menores larguras levaram-nos a produzir guia de onda PEDESTAL utilizando SiO2 como máscara de corrosão do silício que permitiram redução significativa das irregularidades lateral; neste caso foi possível medir a perda e o ganho em guias com largura de até 1 µm. Acrescenta-se que guias de 6 µm tiveram aumento do ganho em 50% na presença de nanopartículas de ouro, atingindo 7,5 dB/cm para potência de bombeamento de 60 mW, portanto inferior à utilizada para o caso do guia sem nanopartículas de ouro, cuja saturação do ganho ocorreu em 100 mW. Guias com nanopartículas de prata foram também produzidos, obtendo-se ganho máximo de 4,0 dB/cm para um guia de 80 µm. Os resultados obtidos nos guias de onda PbO-GeO2 codopados com Er3+ e Yb3+ são promissores e mostram possibilidade de aplicação dos guias de onda como amplificadores ópticos na terceira janela de telecomunicações. / This work presents the production and investigation of optical properties of erbium and ytterbium ions codoped PbO-GeO2 waveguides, containing metallic nanoparticles (NPs), for applications as photonic devices in the third window Telecommunications (1530 nm). The waveguides were obtained by microelectronics conventional processes and by RF Magnetron Sputtering technique using a pedestal type structure. The first pedestal waveguides presented irregulaties, in the lateral region, that contributed to the propagations losses enhancement. Changes in the fabrication process, as the decrease of the chromium used for SiO2 corrosion, additional step for the etching and decrease of the waveguide thickness provided reduction of the propagation losses and enhancement of the optical gain of about 50%; so we obtained 6.0 dB/ cm, at 1530 nm, for 80 µm waveguide width. The difficulty to measure waveguides with smaller width lead us to develop PEDESTAL waveguides using SiO2 as silicon mask for corrosion enabled the decrease of the roughness nearby the core. In this case it was possible to measure propagation losses and gain for waveguides width of 1 µm. It was obtained enhancement of 50 % for the waveguides with 6 µm width in the presence of gold NPs and the result was 7.5 dB/cm at 60 mW pumping power; for the case of the waveguide without gold NPs gain saturation occurred at 100 mW. Waveguides with silver NPs were also produced and the maximum gain was of 4.0 dB/cm for 80 µm. These results show the possibility of using Er3+and Yb3+ codoped PbO-GeO2 pedestal type waveguides as optical amplifiers in the third telecommunications window.
9

Produção e caraterização de materiais vítreos de germanato com nanopartículas metálicas e íons de érbio para aplicações em fotônica. / Production and characterization of germanate glasses with metallic nanoparticles and erbium ions for photonic applications.

Davinson Mariano da Silva 28 September 2007 (has links)
Neste trabalho são apresentadas a preparação e investigação das propriedades luminescentes dos sistemas vítreos PbO-GeO2 e PbO-GeO2-Ga2O3 dopados com íons de érbio e contendo nanopartículas (NPs) metálicas de prata, ouro e cobre, para aplicações em dispositivos fotônicos. Estes vidros apresentam larga janela de transmissão (400-4500nm), alto índice de refração (~1,9) e baixa energia de fônon (700cm-1). Com a finalidade de verificar a nucleação das nanopartículas metálicas, foram realizadas análises por Microscopia Eletrônica de Transmissão que indicaram a presença de nanopartículas metálicas, cristalinas, aproximadamente esféricas e com tamanho médio entre 2 e 10nm. As medidas de absorção óptica evidenciaram a incorporação dos íons de Er3+ na forma trivalente e a presença de bandas de absorção relacionadas à ressonância dos plasmons superficiais, localizadas em aproximadamente 470nm (no caso das NPs de prata) e em torno de 800nm (no caso das NPS de cobre). As medidas de emissão foram realizadas através da excitação das amostras com laser cw de 980nm e potência de 80mW. Foram medidas bandas de emissão associadas à conversão ascendente de freqüências do Er3+ em 530, 550 e 670nm devidas às transições 2H11/2->4I15/2, 4S3/2->4I15/2 e 4F9/2->4I15/2 respectivamente. Nas amostras contendo NPs de prata, para concentrações de 1,0 e 2,0% de AgNO3, foi observado aumento significativo da emissão da luz verde (530 e 550nm) com o crescimento do tempo de tratamento térmico, quando comparadas com a emissão em 670nm. Para as amostras com NPs de ouro, com concentrações de 0,5 e 1,0% de Au2O3 verificamos um aumento maior da emissão em 670nm quando comparada com as emissões em 530 e 550nm. Para amostras com NPs de cobre, as emissões associadas à conversão ascendente de freqüências do Er3+ foram igualmente afetadas pela presença das NPs e possuem intensidade significativamente inferior as dos casos anteriores. O estudo da variação da intensidade de fluorescência com a potência do laser de excitação nos permitiu concluir que dois fótons participam do processo de conversão ascendente de freqüências na presença e na ausência de NPs metálicas. Os aumentos ocorridos na luminescência são provavelmente causados pelo aumento do campo local nas proximidades dos íons de terras-raras devido ao tamanho observado para as NPs (2-10nm). Portanto, a presença das NPs metálicas desempenha papel fundamental no aumento e/ou diminuição da luminescência da conversão ascendente de freqüências dos íons de Er3+, conferindo aos vidros propriedades novas que são bastante interessantes para aplicações em dispositivos fotônicos. / This work presents the preparation and investigation of the luminescent properties of PbO-GeO2 and PbO-GeO2-Ga2O3 vitreous systems, doped with Erbium ions and containing silver, gold and copper metallic nanoparticles (NPs), for applications in photonic devices. These glasses have a large transmission window (400-4500nm), high refractive index (~1,9) and low phonon energy (700cm-1). Transmission Electronic Microscopy analysis were performed, to verify the metallic NPs nucleation. This analysis indicated that the NPs are metallic and crystalline, approximately spherical, with average size between 2 and 10nm. Optical Absorption measurements showed the Er3+ ions incorporation are in trivalent form and the presence of the absorption bands related to the surface plasmon resonance (SPR) centered around 470nm (for silver NPs) and around 800nm (for copper NPs). Emission measurements were performed pumping the samples with a cw laser (980nm; 80mW). Bands associated to Er3+ frequency upconversion centered around 530, 550 and 670nm were observed due to the transitions 2H11/2 -> 4I15/2, 4S3/2 -> 4I15/2 e 4F9/2 -> 4I15/2, respectively. For the samples containing silver NPs, for 1,0 and 2,0% of AgNO3, it was observed a higher enhancement of the green emission (530 and 550nm), with the increasing of the annealing time, when compared to the emission at 670nm. The samples with 0,5 and 1,0% of Au2O3 showed higher enhancement of the emission centered at 670nm, when compared to the emissions at 530 and 550nm. For the samples with copper NPs, the Er3+ emissions were uniformly affected by the presence of the NPs, and have lower intensity than the other ones. The study of the variation of the fluorescence intensity with the pump laser power indicated that two photons are involved in the frequency upconversion process in the presence and in the absence of the metallic NPs. The observed enhancements in the luminescence are probably due to the local field enhancement in the proximities of the rare-earth ions, due to the small size observed for the NPs (2-10nm). Thus, the presence of metallic NPs plays an important role in the enhancement and/or quenching of the Er3+ frequency upconversion, given new properties to glasses which are of great interest for application in photonic devices.
10

Produção e caraterização de materiais vítreos de germanato com nanopartículas metálicas e íons de érbio para aplicações em fotônica. / Production and characterization of germanate glasses with metallic nanoparticles and erbium ions for photonic applications.

Silva, Davinson Mariano da 28 September 2007 (has links)
Neste trabalho são apresentadas a preparação e investigação das propriedades luminescentes dos sistemas vítreos PbO-GeO2 e PbO-GeO2-Ga2O3 dopados com íons de érbio e contendo nanopartículas (NPs) metálicas de prata, ouro e cobre, para aplicações em dispositivos fotônicos. Estes vidros apresentam larga janela de transmissão (400-4500nm), alto índice de refração (~1,9) e baixa energia de fônon (700cm-1). Com a finalidade de verificar a nucleação das nanopartículas metálicas, foram realizadas análises por Microscopia Eletrônica de Transmissão que indicaram a presença de nanopartículas metálicas, cristalinas, aproximadamente esféricas e com tamanho médio entre 2 e 10nm. As medidas de absorção óptica evidenciaram a incorporação dos íons de Er3+ na forma trivalente e a presença de bandas de absorção relacionadas à ressonância dos plasmons superficiais, localizadas em aproximadamente 470nm (no caso das NPs de prata) e em torno de 800nm (no caso das NPS de cobre). As medidas de emissão foram realizadas através da excitação das amostras com laser cw de 980nm e potência de 80mW. Foram medidas bandas de emissão associadas à conversão ascendente de freqüências do Er3+ em 530, 550 e 670nm devidas às transições 2H11/2->4I15/2, 4S3/2->4I15/2 e 4F9/2->4I15/2 respectivamente. Nas amostras contendo NPs de prata, para concentrações de 1,0 e 2,0% de AgNO3, foi observado aumento significativo da emissão da luz verde (530 e 550nm) com o crescimento do tempo de tratamento térmico, quando comparadas com a emissão em 670nm. Para as amostras com NPs de ouro, com concentrações de 0,5 e 1,0% de Au2O3 verificamos um aumento maior da emissão em 670nm quando comparada com as emissões em 530 e 550nm. Para amostras com NPs de cobre, as emissões associadas à conversão ascendente de freqüências do Er3+ foram igualmente afetadas pela presença das NPs e possuem intensidade significativamente inferior as dos casos anteriores. O estudo da variação da intensidade de fluorescência com a potência do laser de excitação nos permitiu concluir que dois fótons participam do processo de conversão ascendente de freqüências na presença e na ausência de NPs metálicas. Os aumentos ocorridos na luminescência são provavelmente causados pelo aumento do campo local nas proximidades dos íons de terras-raras devido ao tamanho observado para as NPs (2-10nm). Portanto, a presença das NPs metálicas desempenha papel fundamental no aumento e/ou diminuição da luminescência da conversão ascendente de freqüências dos íons de Er3+, conferindo aos vidros propriedades novas que são bastante interessantes para aplicações em dispositivos fotônicos. / This work presents the preparation and investigation of the luminescent properties of PbO-GeO2 and PbO-GeO2-Ga2O3 vitreous systems, doped with Erbium ions and containing silver, gold and copper metallic nanoparticles (NPs), for applications in photonic devices. These glasses have a large transmission window (400-4500nm), high refractive index (~1,9) and low phonon energy (700cm-1). Transmission Electronic Microscopy analysis were performed, to verify the metallic NPs nucleation. This analysis indicated that the NPs are metallic and crystalline, approximately spherical, with average size between 2 and 10nm. Optical Absorption measurements showed the Er3+ ions incorporation are in trivalent form and the presence of the absorption bands related to the surface plasmon resonance (SPR) centered around 470nm (for silver NPs) and around 800nm (for copper NPs). Emission measurements were performed pumping the samples with a cw laser (980nm; 80mW). Bands associated to Er3+ frequency upconversion centered around 530, 550 and 670nm were observed due to the transitions 2H11/2 -> 4I15/2, 4S3/2 -> 4I15/2 e 4F9/2 -> 4I15/2, respectively. For the samples containing silver NPs, for 1,0 and 2,0% of AgNO3, it was observed a higher enhancement of the green emission (530 and 550nm), with the increasing of the annealing time, when compared to the emission at 670nm. The samples with 0,5 and 1,0% of Au2O3 showed higher enhancement of the emission centered at 670nm, when compared to the emissions at 530 and 550nm. For the samples with copper NPs, the Er3+ emissions were uniformly affected by the presence of the NPs, and have lower intensity than the other ones. The study of the variation of the fluorescence intensity with the pump laser power indicated that two photons are involved in the frequency upconversion process in the presence and in the absence of the metallic NPs. The observed enhancements in the luminescence are probably due to the local field enhancement in the proximities of the rare-earth ions, due to the small size observed for the NPs (2-10nm). Thus, the presence of metallic NPs plays an important role in the enhancement and/or quenching of the Er3+ frequency upconversion, given new properties to glasses which are of great interest for application in photonic devices.

Page generated in 0.4876 seconds