Este trabalho teve como principal objetivo a síntese e o estudo do processo de cristalização dos sistemas vítreos B2O3-BaO-SiO2, e B2O3-BaO-SiO2-Al2O3, assim como do sistema B2O3-BaO-SiO2 dopado com cério e prata. Amostras do sistema B2O3-BaO-SiO2 contendo 8 e 15% de SiO2, amostras do sistema B2O3-BaO-SiO2-Al2O3 contendo 2, 4 e 8 mol% de Al2O3 e amostras do sistema B2O3-BaO-SiO2 contendo 15% de SiO2 dopada com cério e prata foram caracterizadas através da técnica de analise térmica diferencial (DTA), difração de raios X (DRX), microscopia óptica (MO), espectroscopia Raman, medidas de transmissão na região do ultra-violeta/visível e medidas de luminescência. O estudo do processo de cristalização revelou que em todas as amostras prevaleceu o mecanismo de cristalização superficial. O tratamento térmico em temperaturas acima de Tg e abaixo de Tc levou a formação de uma única fase cristalina, a fase beta -BaB2O4 (beta-BBO). A morfologia dos cristais da fase beta -BBO presentes na superfície das amostras vítreas depende da quantidade de SiO2 e Al2O3. A amostra dopada com cério e prata quando submetida a radiação proveniente de um laser de HeCd e a um posterior tratamento térmico a 400 ºC apresentou somente um efeito de fotosensibilidade superficial devido a alta absorção dos átomos de cério presentes na amostra. / The main purpose of this work was the synthesis and study of the crystallization process of B2O3-BaO-SiO2 and B2O3-BaO-SiO2-Al2O3 as well cerium and silver co-doped B2O3-BaO-SiO2 glassy systems. Samples of 8 and 15 mol% SiO2-containing B2O3-BaO-SiO2 system, 2, 4 and 8 mol% Al2O3-containing B2O3-BaO-SiO2-Al2O3 system and samples 15% mol % SiO2-containing B2O3-BaO-SiO2 system doped with cerium and silver were characterized by different techniques as differential thermal analysis (DTA), X-ray diffraction (XRD), optical microscopy (OM) and Raman spectroscopy. The study of the crystallization process showed that, in all the prepared samples, surface crystallization was the predominant mechanism. The heat treatment at temperatures above Tg and below Tc led to the formation of a single crystalline phase: beta-BaB2O4 (abbreviated as beta-BBO). The morphology of the crystals that appear at the glass surface depends on the amount of SiO2 and Al2O3 in the systems. When subjected to radiation from a HeCd laser and a subsequent heat treatment at 400 ºC, the glass system doped with cerium and silver, showed a photosensitivity effect on the surface due to high absorption of cerium atoms present on the glass sample.

Utilizando amostras de vidro aluminossilicato, 21SiO2·9Al2O3·58Tb2O3·4,0MgO·3,0B2O3·2,0ZnO·1,0Sb2O3 (mol%) e fluorfosfato, 7,49NaPO3·16,45MgF2·16,38CaF2·17,66SrF2·11,63BaF2·30,39AlF3 (mol%) adicionado de 8Tb2O3 e 0,5Ce2O (mol), foram realizadas medidas de absorção óptica, tempo de vida de emissões e luminescência nas faixas do ultravioleta e visível dos íons Tb3+. As eficiências quânticas das emissões para o íon Tb3+, 0,90 (90 %), para o vidro aluminossilicato e 0,69 (69 %), para o vidro fluorfosfato, foram determinadas a partir das razões entre os tempos de vida experimentais, obtidos da experiência de tempo de vida e os tempos de vida teóricos, obtidos das informações de absorção óptica e teoria de Judd- Ofelt. As informações de absorção óptica também possibilitaram identificar as prováveis excitações e emissões observadas nos espectros de luminescência em ambos os vidros estudados. Para determinação dos tempos de vida teóricos, foi necessário calcular as probabilidades de transições radiativas que dependem dos parâmetros de Judd-Ofelt, cujos valores encontrados foram 2 = (2,4 ± 0,2)10-19 cm2, 4 = (3,4 ± 0,3)10-20 cm2 e 6 = (1,5 ± 0,2)10-20 cm2, para o vidro aluminossilicato, e 2 = (7,7 ± 0,6)10-20 cm2, 4 = (0,61 ± 0,05)10-20 cm2 e 6 = (0,69 ± 0,06)10-20 cm2, para o vidro fluorfosfato. Tais valores mostraram-se compatíveis aos da literatura pesquisada, confirmando os valores satisfatórios das eficiências quânticas das emissões dos íons Tb3+. / Samples of glasses 21SiO2·9Al2O3·58Tb2O3·4,0MgO·3,0B2O3·2,0Si2O·2,0ZnO·1,0Sb2O3 (mole %) aluminosilicate and 7,49NaPO3·16,45MgF2·16,38CaF2·17,66SrF2·11,63BaF2·30,39AlF3 (mole %) fluorphosphate added of 8Tb2O3 and 0,5Ce2O (mole) were studied by optical absorption, luminescence and emissions lifetime measurements for the Tb3+ ions. The quantum efficiencies of the Tb3+ emissions, 0,90 (90 %), for the aluminosilicate glass and 0,69 (69 %), for the fluorphosphate glass, were determined using the emissions lifetimes and theoretical lifetimes, obtained from the experimental optical absorption data and Judd-Ofelt theory. The information obtained from the optical absorption spectra allowed the identification of the more likely excitations and emissions observed in the luminescence spectra of the glasses. For the determination of the theoretical lifetimes it was necessary to calculate the radiactive transition probabilities which are dependent of the Judd-Ofelt parameters, whose values were found as 2 = (2,4 ± 0,2)10-19 cm2, 4 = (3,4 ± 0,3)10-20 cm2 and 6 = (1,5 ± 0,2)10-20 cm2, for the aluminosilicate, and 2 = (7,7 ± 0,6)10-20 cm2, 4 = (0,61 ± 0,05)10-20 cm2 and 6 = (0,69 ± 0,06)10-20 cm2, for the fluorphosphate glasses. The results are in good agreement literature examined, and confirm the satisfactory values of the quantum efficiency for the Tb3+ emissions.

Orientadores: Luiz Carlos Barbosa, Cristiano Monteiro de Barros Cordeiro / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-24T15:49:21Z (GMT). No. of bitstreams: 1 FerenczJunior_JulioAlbertoPeres_M.pdf: 3491630 bytes, checksum: 5d5b5385cd23f50e9a3c39e9e55705e2 (MD5) Previous issue date: 2013 / Resumo: Devido à crescente necessidade de troca de informações, cada vez mais é necessário o desenvolvimento e criação de meios para torna-la mais rápida e eficaz, e é necessário que esta tecnologia seja comercial. Uma alternativa seria utilizar fibras ópticas como um meio para a informação quântica. Para tal, vidros teluritos e nanocristais de diamante apresentam propriedades desejáveis. Neste trabalho foi sintetizado e caracterizado um sistema de vidros teluritos frente algumas propriedades térmicas, ópticas e estruturais, em relação à dopagem por CsCl. Após esta caracterização, foi adicionado nanocristais de diamante na composição vítrea mais adequada e verificado que o método utilizado foi eficaz. Observou-se uma maior estabilidade térmica do sistema, menor densidade, maior janela de transparência óptica e menor índice de refração linear com o incremento da concentração de CsCl na matriz vítrea. Além disso, verificamos por microscopia eletrônica de transmissão que os nanocristais de diamante estão presentes na estrutura do material, quando utilizamos nosso método / Abstract: Due to the growing needed for exchange information it is necessary to develop and create ways being a technology faster, more effective and commercial. An alternative option is the use of fiber optics as a media for quantum information. In order to do it, tellurite glasses and diamond nanocrystals exhibit desirable properties. In this work, we synthesized and characterized a system of tellurite glasses forward some thermal, optical and structural properties towards doping CsCl. After this characterization, we added diamond nanocrystals in glass composition more suitable and we verified if the method was effective. We showed a higher thermal stability, lower density, higher optical transparency window and lower linear refractive index with increasing concentration of CsCl in the vitreous system. Furthermore, by transmission electron microscopy was checked that diamond nanocrystals are present inside the structure of the material, when we use this method / Mestrado / Física / Mestre em Física

No description available.

The main motivation of this thesis is to study the long standing problem of mixed alkali effect (MAE) in oxyfluro vanadate glass systems from the point of view of structural arrangement and to investigate the effect of two rare earth ions, namely, erbium and europium on the structure of tellurium dioxide based glass. In glass science, it is well known that when one alkali in a glass matrix is gradually replaced by another alkali, leads to a non-linear variation in some of the physical properties. There are many a theories trying to explain this effect. Recently the renewed interest lies in explaining MAE in-terms of structural consideration. Rare earth (RE) ion doped glasses are of interest in a variety of applications in photonics because of the special optical properties exhibited by these materials. Atomic like f-f transitions of RE ions depend on the local environment of the these ions. A particular glass matrix may be able to bring out the optical properties of a RE ion better than the other matrix. In this regard structural characterization of a glass matrix with different RE ions for optical properties is of importance. Spectroscopic tech-niques are best suited to investigate structural arrangement in glasses and in this thesis we have used techniques like Raman, electron paramagnetic resonance (EPR), impedance, photoluminescence and UV- visible absorption spectroscopies. The thesis comprises of five chapters and an appendix. Chapter 1 consists of brief introduction of general properties of glasses and their behavior under different spectroscopic techniques. Chapter 2 deals with the sample preparation and the experimental techniques used in this work. Chapter 3 elaborates on the Raman and EPR spectroscopic studies on the structural arrangement of the mixed alkali oxyfluro vanadate glass systems. Chapter 4 focuses on the ac and electrical modulus analysis to study the MAE in the above samples. Chapter 5 deals with the optical spectroscopic techniques used to study the compatibility of RE ions (erbium and europium) with the tellurium dioxide based glass matrix. Chapter 1: Disordered materials pose a challenge to understand their structure mainly because of their random arrangement of the constituent units. In this chapter the glassy systems and the different experimental techniques used to study them are discussed in general. The behavior of glassy systems to the external stimuli in various frequency ranges is highlighted. A short review of mixed alkali effect in glasses mainly covering the advances in the last two decades is given. Brief outline of the theory of Raman, EPR and ac impedance spectroscopy are given. Chapter 2: This chapter discusses the major experimental techniques used in the thesis to study the glass systems at block diagram level. The Raman and EPR spectrometers are discussed. Experimental technique used in ac impedance measurement is outlined. Different methods of preparing glass are listed and melt quenching technique is discussed in detail. Chapter 3: This chapter discusses the results and analysis of Raman and EPR study in oxyfluoro vanadate glasses emphasizing MAE. The glass having batch formula 40V2O5 - 30BaF2 - (30 - x) LiF - xRbF (x = 0 – 30) is prepared by melt quenching technique. Raman spectroscopic study in back scattering geometry is performed to see the effect of alkali ions on the V – O bond length of VO6 polyhedra in the glass. The de-convoluted Raman peaks corresponding to V = O and VO2 are considered and the effect of alkali mixture on these bonds are studied. • The peak shift of V = O and VO2 bonds shows that V = O is affected only a little by the replacement of lithium (Li) by rubidium (Rb), while VO2 bond gets affected to a larger extent. • From the peak shift the most probable value of the bond length and the spread in it are estimated. The bond length corresponding to V = O is found to increase and that of VO2 decrease as a consequence of alkali replacement. • From the FWHM of the corresponding Raman peaks, it is concluded that O - Rb coordination sphere around VO6 polyhedra is more homogeneous than either O – Li or O - Li /Rb coordination. These results are published in J. Non-Cryst. Solids 370 (2013) 6. EPR studies on the samples are carried out in X band frequency and spin – Hamilto-nian parameters were extracted by simulating and fitting the EPR spectra to experimental data using EasySpin which is a Matlab toolbox. • it is observed that the ratio 4gjj=4g?, which is a measure of tetragonality of octa-hedral crystal symmetry of V2O5, varies non-monotonically with Rb content. • A model based on this observation is proposed. The essential idea of this model is that Rb atoms that are substituted for Li atoms initially prefer terminal positions over planar positions. Continued substitution then replaces planar Li atoms. It is seen that this model of “preferential substitution” explains the observation very well. • Another observation is that the EPR signal intensity, which is due to concentration of V4+ ions, also shows non-monotonous behavior with Rb content. This is also explained using preferential substitution, taking into consideration the oxidation states of the vanadium ions. • The value of 4gjj=4g?, is a minimum for all rubidium environments around V2O5, which infers that Rb coordination is more symmetric than all Li or Li−Rb. • A good correlation is found between Raman and EPR study of the above system. These results are published in J. Phys. Chem. A 118 (2014) 573. Chapter 4: The chapter brings out the results of ac conductivity and electrical mod-ulus study of MAE in the glass system mentioned above. The Agilent 4294A precision impedance analyzer operating in frequency range 40 Hz to 110 MHz, is used for per-forming impedance and capacitance experiments carried out in this thesis. Impedance measurements in our studies are performed in sandwich geometry. • Room temperature dc conductivity shows a decrease as Li is replaced by Rb and reaches its minimum - five orders less than its all Li value at 0.33 molar fraction of Rb, which is attributed to MAE. This observation is explained using the structural aspect. • Using the linear response theory the number of mobile ions participating in the conduction is estimated. • Imaginary part of the electrical modulus is fitted to Kohlrausch – Williams – Watts (KWW) relation by using a complex nonlinear least squares fitting procedure given by Bergmann. • The stretching parameter b estimated from the above procedure is found to exhibit MAE. The observed variation in b with Rb mole fraction is explained by taking into considerations the contributions from fast and slow processes, and coupling between different relaxing sites. The manuscript is under preparation. Chapter 5: This chapter illustrates the optical study of RE doped TeO2 based glasses to determine the suitability of a particular RE ion with a given glass matrix. TeO2 based glasses having a general formula (in mol %) 65TeO2 – 5BaF2 – 30ZnF2 (TBZ) were prepared by usual melt quenching technique. RE doping was done at the expense of TeO2. 3 mol % of Eu or Er are added to prepare RE doped glass. Raman, PL, UV-visible absorption studies are carried out on the glass samples. • From the peak shift, intensity variation and FWHM of the Raman spectra of the glass samples it is observed that Eu doped TBZ glass has a greater tendency towards depolymerizing the glass matrix by influencing the conversion of TeO4 units into the formation of TeO3 units. • PL spectra of the glass samples shows emission due to different possible transitions. Position of the peak of the de-convoluted spectra shows the position of the particular Stark component and the FWHM is a measure of the inhomogeneous broadening. • The UV-visible absorption spectra are used to calculate the optical density and fitted to the Mott equation to determine the band edge of the glass samples. It is seen that Eu doped TBZ glass has a lesser band gap than that of Er doped glass. The manuscript is submitted to Bul. Mat. Sci. Appendix : This consists of a collection of details of EDS study carried on the VBL series glasses and some MATLAB codes used to simulate the EPR spectrum for VBL series glasses.

En 2010, une nouvelle méthode de production de verres de chalcogénure transparents dans l'infrarouge a été brevetée, alliant la mécanosynthèse au frittage Spark Plasma Sintering. Ce travail de thèse intègre le transfert de technologie vers la société Diafir dans le cadre d'un projet RAPID, financé par la DGA. Il a pour but un travail d'optimisation des procédés de synthèse et de mise en forme a été mené afin de permettre d'adapter cette technologie innovante à un volume industriel. Les verres de composition Ge28Sb12Se60, 80GeSe2-20Ga2Se3, Te20As30Se50, As2Se3 et As2S3 ont été synthétisés par fusion-trempe, broyés finement puis frittés par SPS. Des disques avec des transmissions comparables au verre obtenu par voie classique ont été obtenus. Des traitements antireflets ont été déposés avec succès à leur surface. Le développement de moules spécifiques au SPS a conduit à la production de lentilles sphériques adaptables à des dispositifs optiques. Ces compositions vitreuses ont ensuite été synthétisées par mécanosynthèse puis frittées par SPS. Les disques obtenus présentant des phénomènes de diffusion récurrents. Les principales causes de diffusion ont été analysées afin d'optimiser le procédé de synthèse par voie mécanique. / In 2010, a new method of production of chalcogenide glasses, transparent in the infrared, has been patented. It combines mechanosynthesis to Spark Plasma Sintering. In this thesis work, there is the technology transfer to the Diafir society included in the RAPID project, founded by the DGA. The aim is to optimize the processes of synthesis and forming in order to adapt this innovating technology to an industrial scale. The glasses of composition Ge28Sb12Se60, 80GeSe2-20Ga2Se3, Te20As30Se50, As2Se3 and As2S3 have been synthetized by melt-quench method then crushedfinely before to be sintered by SPS.

El presente proyecto es de una Óptica con ventas a través de un aplicativo móvil y muestra la viabilidad de su ejecución. Esto se sustenta con la investigación realizada, que permite conocer los canales y problemas actuales que conllevan la compra de productos oftálmicos. Se logró recopilar diferentes opiniones y comentarios, en los cuales se identifica la problemática que tienen los usuarios de lentes al momento de comprar sus productos, el tiempo que toma poder encontrar la montura que desean al precio que pueden pagar les puede tomar varias visitas a distintas ópticas hasta poder encontrar lo que satisface sus necesidades. Este proceso puede tomar más de un día y se invierte mucho tiempo en la compra de este producto. Asimismo, gracias a los experimentos realizados, se encontró que debido a la coyuntura actual por la situación de confinamiento que conlleva la actual pandemia del COVID – 19, muchos usuarios están interesados en realizar la compra de sus lentes oftálmicos a través de internet. Este proyecto no busca cambiar el estilo de compra de los usuarios de gafas, sin embargo, nos enfocamos en brindarle todas las herramientas y facilidades necesarias para que ellos mismos tomen onciencia y se adapten al nuevo modelo de compra que está en tendencia, no solo en lentes, sino también en ropa, accesorios, artículos para el hogar, instrumentos de limpieza, videojuegos, etc. Esta tendencia de compra esta potenciada por la coyuntura del Covid – 19. Ha tenido que pasar una pandemia para que la personas se den cuenta de que el E-commerce es el mejor medio para comprar muchas cosas debido a que no inviertes tanto tiempo en comprarlas, evitas relacionarte con la gente y exponerte al virus, disminuyes costos logísticos y es divertido. En Óptika Virtual generamos el confort que el cliente necesita para poder tener una experiencia cálida y acogedora a pesar de ser una tienda virtual. Se brinda mayor cantidad de opciones a la hora de comprar lentes, esto en cuanto al precio y variedad de monturas. Y por último, representamos un ahorro de tiempo y dinero en cuanto a las logísticas del cliente, ya que, no tendrá que pasar tiempo en el tráfico, caminando o buscando lugares donde comprar lentes. También, no gastará dinero en movilizarse a las tiendas. Para desarrollar este Proyecto, se realizó el análisis correspondiente a los factores que corresponden a esta industria: consumidor, proveedores, competidores y otros factores claves. Asimismo, con el fin de evaluar la viabilidad de este proyecto, se desarrollaron los siguientes planes: Plan Estratégico, Plan de Operaciones, Plan de Marketing, Plan de Recursos humanos, Plan de Responsabilidad social empresarial y Plan Financiero. El resultado de este proyecto, indica que, con una inversión inicial de 100,330 soles en el primer año, se tendría una utilidad neta de 84,968 soles en el primer año, 85,067 soles en el segundo año y 117,054 soles en el tercer año. / "This project is an Optical with sales through a mobile application and shows the feasibility of its execution. This is supported by the research carried out, which allows knowing the current channels and problems that lead to the purchase of ophthalmic products. This project does not seek to change the purchasing style of eyeglass wearers, however, we focus on providing all the tools and facilities necessary for them to become aware of and adapt to the new purchasing model that is trending, not only in glasses, but also in clothing, household items, video games, etc. This buying trend is powered by the Covid juncture - 19. It has had to pass a pandemic for people to realize that E-commerce is the best way to buy many things because you do not spend so much time buying them , you avoid interacting with people and exposing yourself to the virus, you reduce logistics costs and it is fun. At Óptika Virtual we generate the comfort that the client needs to be able to have a warm and welcoming experience despite being a virtual store. More options are offered when buying lenses, this in terms of price and variety of frames. To develop this Project, the corresponding analysis of the factors that correspond to this industry was carried out: consumer, suppliers, competitors, and other key factors. Likewise, in order to evaluate the viability of this project, the following plans were developed: Strategic Plan, Operations Plan, Marketing Plan, Human Resources Plan, Corporate Social Responsibility Plan and Financial Plan. " / Trabajo de investigación

This work focuses on polymer glasses relaxation behavior. Polymethylmethacrylate was chosen as a typical representative of polymer glasses. Relaxation processes were studied by dynamical mechanical spectroscopy and differential scanning calorimetry was used as a supplemental analysis. Relaxation process above Tg and high values of rubberlike plateau modulus were observed in thermomechanical spectra. High temperature relaxation transition was studied from the perspective of thermal history, frequency and axial stress dependence and influence of molecular structure was also investigated. Apparent activation energies of studied processes and their axial stress dependence for polymethylmethacrylate were determined. On the basis of obtained data, a hypothesis was developed which connects high temperature relaxation process with molecular process responsible for strain hardening.

A large set of experimental results obtained by the author and colleagues related to the diffusionrelated effects and phase transformation observed in metallic glasses will be presented and discussed.

No description available.