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Made available in DSpace on 2022-04-28T17:20:25Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-07-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) CeRTEV Tellurite glasses are considered a potential alternative for applications not achieved by SiO2-based glasses, presenting interesting optical properties, such as high linear and nonlinear refractive indexes, extended optical window, being also suitable for metallic nanoparticle growth, like Te-0. When doped with sulfide species, it can benefit the reduction of Te4+ to Te-0, which can be advantageous to synthesize in-situ chalcogenide nanoparticles and quantum dots. This work presents investigations on the reduction of Te4+ to Te-0 in tellurite glasses doped with PbS and PbO/ZnS, and aims to control this redox process through the processing with pulsed fs-laser. Tellurite glass samples were synthesized by melt-quenching technique and the thermal and structural properties were explored by different techniques, such as DSC, Raman scattering spectroscopy and mapping experiment, TEM and SAED. Reduction of tellurium to Te-0 nanocrystals into tellurite glass after laser irradiation was studied in detail and confirmed by the presence of bands at similar to 120 and 140 cm(-1) in Raman spectroscopy and mapping, assigned to the Te-Te vibrational modes, which suggest that S2- induces in-situ Te4+ reduction. Moreover, quasi spherical tellurium nanoparticles were observed through TEM and confirmed their chemical nature and crystallization by SAED. The study of tellurium reduction in the vitreous matrix becomes particularly important and promising for some applications, since its reduction generates changes in the refractive index by precipitation of Te-0 nanoparticles, allowing the fabrication of waveguides and as photosensitive material for tridimensional data storage. (C) 2021 Published by Elsevier B.V. Univ Sao Paulo, Sao Carlos Inst Chem IQSC, Sao Carlos, SP, Brazil Univ Sao Paulo, Sao Carlos Inst Phys IFSC, Sao Carlos, SP, Brazil Univ Sao Paulo, Sao Carlos Sch Engn EESC, Sao Carlos, SP, Brazil Sao Paulo State Univ, Inst Chem, Araraquara, SP, Brazil Univ Fed Alfenas, Grp Quim Mat, Pocos De Caldas, MG, Brazil Sao Paulo State Univ, Inst Chem, Araraquara, SP, Brazil FAPESP: 2018/164076 FAPESP: 2018/11283-7 FAPESP: 2018/16126-7 CeRTEV: 2013/077936

Made available in DSpace on 2022-04-28T19:47:48Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-12-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) Financiadora de Estudos e Projetos Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Structural, optical and photoluminescent properties of Europium-doped potassium germanate glassy materials were investigated in terms of tantalum content and nanoscale crystallization of potassium tantalate K2Ta8O21. For such purpose, an Eu3+-doped germanate glass, Eu3+-doped tantalum germanate glass and Eu3+-doped tantalum germanate glass-ceramics were prepared and characterized by X-ray diffraction, Raman, UV–Vis–NIR and photoluminescence spectroscopies. Eu3+ emission properties were used as a sensitive probe to investigate its symmetry site into the host structure. The chemical microenvironment around Eu3+ ions have changed with tantalum concentration as well as bronze-like tantalum perovskite K2Ta8O21 phase crystallization into the glasses. The ions preferably occupy sites of higher symmetry and lower energy phonons, which attest the ions migration to the tantalum-rich crystalline environment. The correlation between the phonon side band (PSB) spectra and Raman vibrational modes, 5D0 → 7F2/5D0 → 7F1 ratio and experimental Eu3+ 5D0 lifetime support this assumption. The highest photoluminescence intrinsic quantum yield (QEuEu) is calculated for glass-ceramics heat-treated for 20 h by using Judd-Ofelt theory, indicating reduction of nonradiative decay processes due to the lower local phonon energy. The luminescence quenching for longer crystallization times demonstrates the importance of optimizing thermal treatment parameters to ensure proper distance between optically active ions. Accordingly, tantalum germanate glass-ceramics are promising for photonic devices as red laser, solid-state lighting and energy conversion applications, as well as for nonlinear optical applications considering the perovskite bronze-like crystallization. Grupo de Química de Materiais Universidade Federal de Alfenas Campus Poços de Caldas Instituto de Química Universidade Estadual Paulista - UNESP Departamento de Química Faculdade de Filosofia Ciências e Letras de Ribeirão Preto Universidade de São Paulo Instituto de Química Universidade Estadual Paulista - UNESP FAPESP: 2017/11301-2 FAPESP: 2020/01786-1 FAPESP: 2020/05319-9 CNPq: 303110/2019-8

Er3+-doped and Er3+/Yb3+-codoped GeO2-Nb2O5-K2O glasses were prepared by conventional melt-quenching method. Thermal and spectroscopic analysis were performed. The niobium insertion into the glass structure has decreased the OH groups resulting in a slight increase in the luminescence efficiency as the niobium content. Glass network structure is modified depending on rare earth doping concentration and niobium content. The number of bridge oxygen bonds and nonbridge oxygen bonds is altered and consequently the crystallization composition. The spectroscopic features were discussed in terms of niobium concentration and its influence on the applications as optical devices. The addition of niobium broadens the emission band in the region of 1.5 µm covering C, S and L-telecommunication bands. The gain coefficient has calculated establishing high potentiality to use the niobium germanate glasses for optical amplification. The codoping by Er3+/Yb3+ intensifies the emission in the NIR and visible (upconversion) region in relation to the doped samples and may be interesting for application as visible and near-infrared emitters. In addition, the codoped samples with variable niobium contents have potential as visible tunable phosphors emitting either green or red light. Accordingly, the niobium germanate glasses are interesting matrices for rare earth ions doping and for the development of optical devices, such as visible and NIR laser and optical amplifiers.

International audience; Complex sequential crystallization mechanisms were investigated in the glass composition 70GeO2-10Na2O-20Ta2O5 prepared by melt-quenching. In a first stage, a classical volume-nucleated crystallization of sodium tantalate perovskite Na2Ta8O21 is induced under short time heat-treatments whereas longer annealing treatments promote the formation of surface spherical structures known as spherulites. These singular glass-ceramics were deeply investigated by density measurements, differential scanning calorimetry (DSC), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), Auger Electron Spectroscopy (EDS), correlated Raman and second harmonic generation (SHG) microscopy as well as macro-SHG measurements. These surface spherulites with average size up to 50 µm are richer in tantalum but poorer in germanium than the surrounding material. However, measured SHG signals were found to be related to quartz-like α-GeO2 grown inside the spherulites. Therefore these materials exhibit a second-order non-linear optical response, related to the symmetry of the point group D3 given by the quartz GeO2 grown for the first time in a transparent glass-ceramic.

CdTe/Er3+-codoped SiO2–Nb2O5-based nanocomposites were prepared by a sol-gel route. The thermal, structural and photophysical properties were investigated by FTIR spectroscopy, N2 adsorption/desorption isotherms, XRD, TGA and DSC analysis, TEM images, UV–Vis spectroscopy, and photoluminescence. The influence of QDs content and niobium/erbium addition on these properties were studied. It is shown that the QDs content into the nanocomposites influences their average size and photoluminescence properties. High QDs content resulted in larger nanocomposite pore size and higher QDs average size. The average pore size created by QDs-doped samples has dimensions suitable for QD adsorption. The TEM images and photoluminescence results demonstrate the successful incorporation of CdTe QDs into the SiO2–Nb2O5 host, which results in a homogeneous nanocomposite material presenting tunable fluorescence in the range of 513–568 nm in function of QD content. Furthermore, CdTe-doped SiO2–Nb2O5-based mesoporous nanocomposite allows the QD chemical stability capped by MPA. These nanocomposites may have a potentially broad application as photonic devices, such as broadband emission devices, optical amplification and lighting.

Transparent fluorotellurite glasses were prepared by melt-quenching in the ternary system TeO2-Nb2O5-PbF2. The synthesis conditions were adjusted to minimize fluorine loss monitored as HF release. It was found that 10 mol% of Nb2O5 is the optimum content for PbF2 incorporation up to 35 mol% in the tellurite matrix without loss of glass forming ability. Such glass compositions exhibit a wide optical window from 380 nm to about 6 &mu, m. Crystallization properties were carefully investigated by thermal analysis and compositions with higher PbF2 contents exhibit preferential precipitation of lead oxyfluoride Pb2OF2 at lower temperatures. The lead oxyfluoride crystallization mechanism is also governed by a volume nucleation, barely reported in tellurite glasses. Eu3+ doping of these glass compositions also promotes a more efficient nucleation step under suitable heat-treatments, resulting in transparent Eu3+-doped glass-ceramics whereas undoped glass-ceramics are translucent. Finally, Eu3+ spectroscopy pointed out a progressive, more symmetric surrounding around the rare earth ions with increasing PbF2 contents as well as higher quantum efficiencies. These new fluorotellurite glass compositions are promising as luminescent hosts working in the middle infrared.

Made available in DSpace on 2020-12-12T01:28:31Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-11-25 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) Financiadora de Estudos e Projetos Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Transparent Eu3+-doped tantalum phosphate glass-ceramics containing Na2Ta8O21 nanocrystals were successfully obtained by a two-step heat treatment. Structural analyses were performed using X-ray diffraction, Transmission Electron Microscopy, Nuclear Magnetic Resonance and Raman spectroscopy. Due to the high Ta/P ratio (= 2) the glass network is built from a mixed 3D PO4–TaO6 chain in which TaO6-rich regions are inserted and responsible for crystallization of an alkali tantalum oxide phase Na2Ta8O21. Eu3+ and their optical properties was used as a sensitive probe to study it site structure in the host matrix. The radiative properties of Eu3+ emission levels were predicted using the Judd-Ofelt theory. The chemical environment and local phonon energy around the rare-earth ions have been proposed based on phonon side band associated with the 7F0 → 5D2 transition, 5D0 → 7F2/7F1 relative intensity and narrowing of the emission bands. High tantalum content precursor glass exhibits high photoluminescence quantum efficiency due to low phonon energy and high refractive index (1.9461 at 633 nm). A perovskite-like bronze crystalline structure is formed in the glass-ceramic (nucleated at 925 °C for 0.5 h and grown at 940 °C for different times) and is considered promising for nonlinear optical applications and studies. Institute of Chemistry Sao Paulo State University - UNESP Sao Carlos Institute of Chemistry University of Sao Paulo, São Carlos Grupo de Química de Materiais Universidade Federal de Alfenas Campus Poços de Caldas, Poços de Caldas Institute of Chemistry Sao Paulo State University - UNESP CNPq: 156420/2018-0 FAPESP: 2013/07793-6 FAPESP: 2018/16126-7

Made available in DSpace on 2020-12-10T17:34:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-07-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) FINEP Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Alkali niobium germanate glasses were prepared by melt-quenching in the ternary systems 75GeO(2)-15Nb(2)O(5)-10M(2)O with M = Li, Na, K, Rb and Cs. Thermal properties of these glasses and related glass-ceramics are strongly dependent on the alkaline modifier. Structural investigations by Raman allowed to determine that the alkali radius has an influence on the number of non-bridging oxygens and consequently on the average glass network connectivity. Raman spectra of sodium, potassium and rubidium germanate glass-ceramics exhibited slight changes when compared to the pristine glass and the new Raman features can be attributed to a 3D NbO6 network similar to orthorhombic niobium oxide. Characterization of the heat-treated glasses allowed to determine the crystalline phases precipitated in the samples and it has been shown that a single perovskite bronze-like phase of general formula M2Nb5O21 can be obtained in Na, K, and Rb-containing glasses. Luminescent properties of Eu3+-doped glasses pointed out a non-regular tendency where sodium-based glass seems to be the inflexion point of luminescent data with higher asymmetry around Eu3+ ions and higher quantum efficiency. In transparent glass-ceramics, the Eu3+ luminescent properties are clearly modified in the Na- and K-based samples with lower symmetry and quantum efficiency after heat-treatment. Such optical behavior is attributed to Eu3+ migration in the perovskite crystalline phase with highly distorted Eu3+ sites and shorter Eu3+-Eu3+ distances. Univ Fed Alfenas, Grp Quim Mat, Campus Pocos De Caldas, Pocos De Caldas, MG, Brazil Univ Estadual Paulista, Inst Quim, Araraquara, SP, Brazil Univ Estadual Paulista, Inst Quim, Araraquara, SP, Brazil CNPq: 156420/2018-0

N-doped ZnO is a prospective material for photocatalytic reactions. However, only oxidative paths are well investigated in the literature. This paper describes a comparative study about ZnO and ZnO:N potential for oxidative and reductive reactions, probed by rhodamine B dye photodegradation and CO2 photoreduction. The materials were prepared by the polymeric precursor method, using urea as a nitrogen source, and different heat treatments were used to observe their effects on surface decontamination, crystallinity, particle sizes and shapes, and photocatalytic performance. ZnO and ZnO:N presented a wurtzite crystalline structure and nanometric-scale particles. Samples submitted to higher temperatures showed lower specific surface areas, but higher crystallinity and lower contents of species adsorbed on their surfaces. On the other hand, the photocatalysts annealed in shorter times presented smaller crystallite sizes and lower crystallinity. These factors influenced the photoactivity in both conditions, i.e., oxidation and reduction reactions, under the ultraviolet and visible light, indicating that structural factors influenced the adequate charge separation and consequent photocatalytic activity since the as-synthesized samples were versatile photocatalysts in both redox reactions.

High photoluminescence efficiency, unusual NIR broadband and tunable emission are possible in erbium-doped and tantalum germanate glasses and nanostructured glass-ceramics. The chemical microenvironment around erbium ions and their influence on optical properties are dependent on the TaO6 clusters formation and tantalum perovskite-like bronze crystallization, which are strongly related to the tantalum oxide content and annealing. Erbium ions are preferably distributed close to tantalum-rich environment, providing an intense emission with minimized nonradiative processes and inhomogeneous broadband NIR emission with increasing site numbers. A more pronounced broadening in the nanocrystalline samples is due to the multi-sites of the tantalum perovskite-like bronze crystalline structure. Green/red tunable emission from up conversion processes was observed since the erbium ions occupy a chemical environment with low phonon energy in the tantalum germanate glass and with close neighbors in the tantalum germanate glass-ceramics. Accordingly, the highly tantalum germanate glasses and glass ceramics are promising for photonic applications in optical amplification, lighting and lasing, as well as for nonlinear optical applications and studies considering the perovskite-like bronze crystalline samples.

International audience; Structure, linear and nonlinear optical properties of glasses in the ternary system (90–x)GeO2–10Na2O–xTa2O5 have been investigated. These glasses exhibit a wide transparency window from 350 to 5500 nm and refractive index ranging from 1.78 to 1.93. Upon a thermal poling treatment under nitrogen atmosphere using increasing poling voltages, second harmonic generation (SHG) quantitative measurements were performed and have confirmed the electro-optical origin of the second-order optical responses; χ(2) values ranging from 0.06 to 0.3 pm/V were obtained, depending on the poling conditions and glass composition. SHG/Raman correlated microscopy measurements allowed identification of the structural changes within the poled layer and pointed out that sodium depletion led to a more connected glass network through cross-linking bonds such as Ge–O–Ge and Ta–O–Ta bonds. A deviation from a pure electro-optical second-order response is observed for the highest poling voltage. In this particular case, a linear optical birefringence and a structural χ(2) might have to be taken into account to describe accurately the polarized layer optical properties.

Eu3+-, Er3+-doped and Er3+/Yb3+-codoped niobium alkali germanate glasses, in the compositional host system GeO2-Nb2O5-K2O were synthesized by the conventional melt-quenching technique. Glass-ceramics were manufactured by controlled heat treatment of the precursor glasses. Homogeneous glasses and nanocrystalline glass-ceramics were investigated by DSC, XRD, TEM and spectroscopic analysis. K2Nb14O36 crystals are formed in the prepared glass-ceramics. This crystalline phase has low phonon energy as compared to the precursor glass and a variety of chemical sites for rare-earth ions. In glass-ceramics, the rare-earth ions occupy higher symmetry sites of the K2Nb14O36 nanocrystals resulting in inhomogeneous broadband emissions. Judd-Ofelt parameters were obtained for the Eu3+- and Er3+-doped samples. Glass-ceramics heat-treated for 20 h exhibited the highest photoluminescence quantum efficiency. The increased quantum efficiency is due to the decrease of nonradiative decay processes, that depopulate the excited levels, as well as the decrease in hydroxyl content and overall phonon energy. However, luminescence quenching is verified for samples with longer crystallization times, which emphasizes the importance of optimized heat treatment parameters. The gain coefficient and upconversion data were obtained and corroborate the potential application of these materials as photonic devices, such as visible and NIR laser and optical amplifiers.

The green emissions of the trivalent erbium ions exhibit promising applications in photonics, such as the development of solid-state lasers, optical sensors, and light-emitting diodes (LED). In this work, the intensity of the emissions of two thermally coupled levels 2H11/2 and 4S3/2 excited states of Er3+ ions are studied in Er3+/Yb3+ co-doped tungsten sodium phosphate oxyfluoride glasses. The results demonstrate that an increase in the content of the PbF2 leads to an enhancement in the performance of these samples as optical sensors, and amplifies the relative thermal sensitivity from 0.82% K−1 to 1.15% K−1 for glass samples containing 10 mol% and 50 mol% of PbF2, respectively. Additionally, the effect of PbF2 is discussed in terms of the modifications of the site symmetries around Er3+ ions and changes in the energy gap between the thermally coupled levels, which implied in the improvement of the absolute thermal sensitivity at higher temperatures for high PbF2 contained sample.

We report on the influence of silver nanoparticles (NPs) on the luminescence behavior of trivalent rare earth (RE) ion doped tungsten-phosphate glasses. In order to induce the growth of NPs, the as-prepared glass samples containing silver atoms, are exposed to heat-treatment above the glass transition temperature. The surface plasmon resonance band of the Ag NPs is observed in the visible range around 420 and 537 nm in the glasses with low and high tungsten content, respectively. Such difference in spectral shift of the plasmon band is attributed to the difference in the refractive index of the two studied glass compositions. Heat-treatment results in the general increase in number of NPs, while in the case of glasses with low tungsten content, it also imposes a shift to the Ag plasmon band. The NPs size distribution (4–10 nm) was determined in good agreement with the values obtained by using Mie theory and by transmission electron microscopy. The observed quenching in the visible luminescence of glasses doped with Eu3+, Tb3+ or Er3+is attributed to energy transfer from the RE ions to Ag species, while an enhanced near-infrared emission in Er3+ doped glasses is discussed in terms of the chemical contribution of silver, rather than the most commonly claimed enhancement of localized field or energy transfer from silver species to Er3+. The results are supported by the lifetime measurements. We believe that this study gives further insight and in-depth exploration of the somewhat controversial discussions on the influence of metallic NPs plasmonic effects in RE-doped glasses.

Tungsten-phosphate glasses doped with different rare earth ions (Er3+, Eu3+, Nd3+ and Tb3+) were obtained by the conventional melt-quenching technique. At high amounts of tungsten oxide (>50 mol%), the tungsten-phosphate glasses are only translucent due to reduced W5+ species. However, the transparency of the glasses is significantly increased by the addition of Sb2O3 - as an oxidating agent which promotes the conversion of W5+ into W6+. FTIR spectra allowed identification of absorption bands corresponding to phosphate structural groups and tungsten units in the 500–1300 cm−1 spectral region. The optical absorption, luminescence excitation and emission spectra were collected and Judd-Ofelt analysis was carried out for selected samples. It is observed that by increasing the amount of WO3, the lifetime of the Er3+ NIR emission increases as well as the branching ratio of Eu3+ emission band at 610 nm, respectively, due to lowering of the average phonon energy of the glassy system and increasing of the site asymmetry around the rare earth ions. Details on the photophysics of these glasses, including upconversion and the analysis of radiative properties via Judd-Ofelt calculations are given and discussed as a function of structural variations and dopant ion concentrations.

Glasses in the binary system KPO3-Ta2O5 were prepared by the melt-quenching technique. Highly modified phosphate glasses with up to 40 mol% Ta2O5 were obtained. The samples were characterized by Differential scanning calorimetry (DSC) and X-ray powder diffraction (XRD) analysis, Ultraviolet–Visible (UV–Vis) and infrared (IR) transmittance, Raman and luminescence spectroscopies. Thermal, structural and optical properties are strongly dependent of the tantalum oxide content. Thermal behavior and Raman data are in agreement with a progressive insertion of tantalum units in the phosphate network through P-O-Ta bonds. These bonds enhance the network connectivity due to TaO6 units cross-linking the linear phosphate chains. In addition, higher Ta2O5 contents in the glass network results in tantalum oxide-rich regions detected as Ta-O-Ta bridging bonds, apparently acting as crystallization nuclei. Emission spectra of Eu3+-doped glasses pointed out a decrease in the symmetry of the Eu3+ sites by increasing Ta2O5 content. A decrease in the excited state lifetimes was also identified due to the progressive Ta-rich environment around Eu3+ ion. Finally, photoluminescence quantum efficiency increases with tantalum insertion due to the reduction of local phonon energy around rare-earth ions. In this sense, high tantalum phosphate glasses are built up from TaOx polyhedra within the phosphate chains. The presence of TaOx clusters allows the improvement of optical and thermal properties and corroborates with the potential application of these materials photonic devices.

Made available in DSpace on 2018-12-11T16:54:32Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-10-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) Financiadora de Estudos e Projetos The evolution of research on luminescent phosphors led to research on materials doped with rare earth ions (RE3+), not only because of their photoluminescent properties, but also for their potential applications in photonics. The search for new photoluminescent materials has led to an investigation of the photoluminescence of RE3+ present in an aluminum oxide (Al2O3) matrix. This oxide has a transparent window on the short ultraviolet to near infrared, excellent mechanical properties and good chemical stability. Within this context, this work aims to obtain Al2O3: Er3+/Yb3+. The preparation of Al2O3: Er3+/Yb3+ involved two synthesis processes. For the co-precipitation process, rings of aluminum cans were used as precursors, and for the sol-gel process, the precursor used was tri-sec-butoxide aluminum. From the XRD results, high heat-treatment temperatures were observed to favor the formation of the α-Al2O3 phase and low temperatures were observed to favor the formation the γ-Al2O3 phase. The analysis of the photoluminescence emission spectra when excited at 980 nm, showed the up-conversion phenomenon with an emission in the visible region. The emission spectra also showed emission between 1400 and 1650 nm, with a maximum at about 1530 nm. The materials exhibit efficient energy absorption in the infrared region, with light emission in the visible region. Furthermore, the spectra show an intense emission in the infrared region assigned to the 4I13/2 → 4I15/2 transition of Er3+, demonstrating excellent potential to be used in optical amplifier device at the third telecommunications window. Grupo de Pesquisa em Química de Materiais – (GPQM) Departamento de Ciências Naturais Universidade Federal de São João del-Rei Campus Dom Bosco, Praça Dom Helvécio, 74 Instituto de Química UNESP, P.O. Box 355 Research Group of Materials Chemistry Universidade Federal de Alfenas, Campus de Poços de Caldas Departamento de Química Faculdade de Filosofia Ciências e Letras de Ribeirão Preto USP, Avenida Bandeirantes, 3900 Department of Chemistry and Physics University of Tennessee at Martin Desenvolvimento de Materiais Inorgânicos com Terras Raras - DeMITeR Instituto de Química – (IQ) Universidade Federal de Uberlândia – (UFU), Av. João Naves de Ávila, 2121 – Bairro Santa Mônica Instituto de Química UNESP, P.O. Box 355 FAPEMIG: CEX - RED-00010-14

Made available in DSpace on 2018-11-28T15:26:08Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-05-01 Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) FINEP (CT-INFRA) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) New glass compositions were investigated in this specific proportion (90-x)TeO2-10GeO(2)-xPbF(2) in order to study the influence of lead fluoride content on the thermal, structural and optical properties. Glass samples with x = 5 to 30% were prepared by melt-quenching method. Thermal characterizations by DSC allowed to identify a clear decrease of the glass transition temperature as well as a very distinct crystallization behavior for higher PbF2 contents. Raman spectroscopy suggests a progressive PbF2 incorporation with conversion of TeO4 to TeO3 units related with the modifier behavior of PbF2 in the glass network. X-ray diffraction patterns of crystallized samples support these results since crystalline TeO2 was detected for lower PbF2 contents whereas lead tellurite Pb2Te3O7 was identified for the most lead fluoride concentrated sample. UV-Vis-MR absorption spectra are in agreement with a progressive increase of the optical bandgap with lead fluoride concentration. Emission spectra of Eu3+ doped samples also pointed out a progressive structural change around Eu3+ ions with more symmetric sites. Finally, experimental lifetimes, Judd-Ofelt parameters and quantum efficiencies were obtained from these samples and exhibited a strong dependency of the lead fluoride contents, suggesting that these new fluorotellurite glasses are interesting hosts for rare earth ions. (C) 2017 Elsevier B.V. All rights reserved. Univ Fed Alfenas, Grp Quim Mat, Campus Pocos de Caldas, Pocos De Caldas, MG, Brazil Univ Sao Paulo, Fac Filosofia Ciencias & Letras Ribeirao Preto, Dept Quim, Av Bandeirantes 3900, BR-14040901 Ribeirao Preto, SP, Brazil Univ Estadual Paulista, Inst Quim, Araraquara, SP, Brazil Univ Estadual Paulista, Inst Quim, Araraquara, SP, Brazil FAPEMIG: CEX-APQ-01410-12 CNPq: 552225/2011-8

In this work, the glass forming ability was studied in potassium phosphate glasses with increasing amounts of TiO2 in order to obtain a glass-ceramic with photocatalytic properties. The first studied series has been the binary system (100-x) KPO3-xTiO2. Homogeneous and transparent glasses could be obtained with x varying from 10 to 30 mole%. Since the photocatalytic anatase phase could not be precipitated in this system, the ternary system KPO3-TiO2-Nb2O5 was investigated in order to incorporate higher TiO2 contents without spontaneous crystallization under cooling. Thermal properties of all glass samples were investigated by DSC and allowed identifying an increase of glass transition temperatures with increasing TiO2. For all compositions, exothermic events related with crystallization were also observed and suitable heat-treatments resulted in specific crystalline phases identified by X-ray diffraction. Selective precipitation of the anatase titanium oxide was successfully obtained from the glass compostion 35KPO3-25Nb2O5-40TiO2 (KN25T40) after heat treatment at 720°C for 2 h, suggesting the possibility of obtaining a glass-ceramic for photocatalytic applications. Structural investigations by Raman were also performed on glasses and glass-ceramics and allowed to point out the glass intermediary behavior of TiO2 in the phosphate vitreous network where TiO4 and TiO6 octahedra are inserted inside the phosphate network with TiO6 clusters identified at higher TiO2 contents. Raman analysis also identified anatase TiO2 in the KN25T40 glass-ceramic.

Niobium alkali germanate glasses were synthesized by the melt-quenching technique. The ternary system (90-x)GeO2-xNb2O5-10K2O forms homogeneous glasses with x ranging from 0 to 20mol%. Samples were investigated by DSC and XRD analysis, FTIR and Raman spectroscopy, and optical absorption. Structural and physical features are discussed in terms of Nb2O5 content. The niobium content increase in the glass network strongly modifies the thermal, structural and optical properties of alkali germanate glasses. DSC, Raman and FTIR analysis suggest niobium addition promotes NbO6 groups insertion close to GeO4 units of the glass network. XRD analysis also pointed out that samples containing high niobium oxide contents exhibit preferential niobium oxide rich phase after crystallization after heat treatment, which is similar to orthorhombic Nb2O5. Absorption spectra revealed high transmission range between 400nm to 6.2μm, added to a considerably decreased hydroxyl group content as the addition of niobium in the alkali germanate network. The niobium oxide rich phase crystallization process was studied and activation energy was determined, as well as nucleation and crystal growth temperatures and time for obtaining transparent glass-ceramics. This article is protected by copyright. All rights reserved.

The relentless pursuit for materials containing rare earth ions with photoluminescent properties has led to several studies with applications in the development of new technologies. The main focus of this work is the preparation of Er 3+ -doped polycrystalline Y 2 O 3 with photoluminescent properties using PEG as an organic precursor and heat-treated at different temperatures. The methodology used in this synthesis is highly attractive due to its high feasibility for improved technology and low cost for preparing materials. The behavior of the viscous resin has been evaluated and the final compounds exhibited the formation of a cubic polycrystalline phase, which is able to support variations in Er 3+ doping concentrations up to 10 mol%, without significant changes in the polycrystalline parameters. The values of the nanocrystallite size calculated by Scherrer׳s equation showed direct dependence on the heat-treatment temperature as well as the Er 3+ concentration. Intense emission in the visible region under excitation at 980 nm was attributed to an upconversion phenomenon assigned to the intraconfigurational f–f transitions of Er 3+ ions. The upconversion mechanism was investigated and it was demonstrated that the higher intense emission in the red region in comparison to the emission in the green region is related to the crystallite size. The studies about the intensity showed the dependence of upconversion emission of power source, indicating that two-photon are responsible for the green and red photoluminescence. These polycrystalline materials exhibit properties that make them promising for use in solar energy systems, C-telecom band or solid-state laser devices.

Made available in DSpace on 2019-10-04T13:15:57Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-10-01 Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) FINEP Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Niobium alkali germanate glasses doped with Er3+ up to 4.0 mol% were synthesized by the melt-quenching technique. Glass-ceramics were obtained by controlled heat treatment of the pristine glass. Thermal and optical properties were investigated and are shown to depend on the erbium content. The main radiative parameters were obtained based on the Judd-Ofelt theory. The change of radiation energy processes and modification of the environment of the earth-rare ion occurs in samples with high erbium concentrations. In general, strong enhancement of upconversion emission occurs due to the efficient process of excited-state absorption for the high erbium content samples. Visible tunable phosphors emitting either red-to-green light depends on the erbium content and heat treatment. In addition, these glasses and glass-ceramics samples have high thermal stability and wide transmission window. For these reasons, Er3+-doped niobium germanate glasses and glass-ceramics may be suitable for photonic device applications, especially as visible laser. Univ Fed Alfenas, Grp Quim Mat, Campus Pocos Caldas, Pocos De Caldas, MG, Brazil Univ Sao Paulo, Fac Filosofia, Dept Quim Ciencias & Letras Ribeirao Preto, Ribeirao Preto, SP, Brazil Univ Sao Paulo, Inst Fis Sao Carlos, Sao Carlos, SP, Brazil Univ Sao Paulo, Inst Quim Sao Carlos, Sao Carlos, SP, Brazil Univ Estadual Paulista, Inst Quim, Araraquara, SP, Brazil Univ Estadual Paulista, Inst Quim, Araraquara, SP, Brazil FAPESP: 2013/07793-6

The main objective of this work has been to prepare and characterize the thermal and structural properties of glasses in the pseudo binary system TeO 2 –Pb(PO 3 ) 2 with respect to the composition. Homogeneous and transparent glass samples were obtained by the melt-quenching method in a large glass forming range in the pseudo binary system (100 − x )TeO 2 – x Pb(PO 3 ) 2 with x varying from 5 to 100. Thermal properties investigated by DSC pointed out an increase of the glass transition temperature from x = 5 to x = 40 and further decrease of Tg for higher Pb(PO 3 ) 2 concentrations. A similar tendency has been observed for the thermal stability against devitrification measured using the stability parameter Tx–Tg. FTIR together with Raman spectroscopies allowed building a structural model for these glasses with the contribution of distinct phosphate and tellurite units depending on the composition. Identification of crystalline phases obtained after the glasses heat-treatments obtained by X-ray diffraction support the structural evolution suggested by vibrational spectroscopies. These data suggest that incorporation of TeO 2 in the lead metaphosphate glass results in tellurium conversion from TeO 4 seesaw geometry to TeO 3 trigonal pyramids and consequent conversion of well-known metaphosphate units Q 2 to modified pyrophosphate units Q 2 1Te in which the phosphorus PO 4 tetrahedron is linked to another PO 4 unit and one TeO 3 pyramid. These tellurite trigonal units cross-link the modified metaphosphate chains with a resulting increase of the glass network connectivity. For high TeO 2 concentrations, all Q 2 were converted to Q 2 1Te and the additional tellurium atoms are incorporated in the glass network as TeO 4 seesaw units with a glass network built from a tridimensional network of TeO 3 , TeO 4 and Q 2 1Te . Finally, this work pointed out the possibility to use this pseudo-binary system for the preparation of phosphate glass-ceramics containing a TeO 2 crystalline phase or tellurite glass-ceramics containing a pyrophosphate or metaphosphate crystalline phase.

Made available in DSpace on 2018-11-28T01:36:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-12-01 Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) FINEP Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) In this work the novel glass system TeO2-Sb2O3-GeO2 was investigated and promising glass compositions were selected for further specific studies. Glass samples in the (80-0.8x)TeO2-(20-0.2x)Sb2O3-xGeO(2) molar composition were prepared by the melt-quenching method with a glass-forming domain from x = 10 to x = 90. Samples were investigated by XRD, DSC, FTIR, Raman spectroscopy and UV-visible absorption. The XRD and DSC results bring informations about the non-crystalline state and thermal properties of these materials. It has been observed that higher GeO2 contents lead to higher glass transition temperatures and thermal stabilities against crystallization. FTIR and Raman spectroscopies suggest a progressive incorporation of GeO2 in the covalent network of TeO2 with conversion of structural units TeO4 to TeO3. Absorption spectra revealed the high visible transparency of these samples and an increase of the optical band gap with GeO2 addition, in agreement with a decreasing polarizability of the glass network. Er3+ doped and Er3+/Yb3+ codoped samples were also studied with respect to their infrared emission properties and higher GeO2 contents lead to an increase in IR emission intensity at 1,5 mu m as well as longer radiative lifetimes. Finally, upconversion emission in the visible were also recorded and were shown to be strongly dependent of the composition. (C) 2016 Elsevier B.V. All rights reserved. Univ Fed Alfenas, Grp Quim Mat, Campus Pocos Caldas, Pocos De Caldas, MG, Brazil Univ Sao Paulo, Dept Quim, Fac Filosofia Ciencias & Letras Ribeirao Preto, Av Bandeirantes, BR-14040901 Ribeirao Preto, SP, Brazil Univ Estdual Paulista Julio Mesquita Filho, Inst Quim, Araraquara, SP, Brazil Univ Estdual Paulista Julio Mesquita Filho, Inst Quim, Araraquara, SP, Brazil

Made available in DSpace on 2018-11-26T17:55:51Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-04-01. Added 1 bitstream(s) on 2021-07-15T14:32:23Z : No. of bitstreams: 1 S0100-40422016000300328.pdf: 5545326 bytes, checksum: 7e6829c8c6880aa7e049f21c77f3decb (MD5) 2015 is the Year of Light, according to UNESCO. Chemistry has a close relationship with light and one of the materials that allows such synergy is glass. Depending on the chemical composition of the glass, it is possible to achieve technological applications for the whole range of wavelengths extending from the region of the microwave to gamma rays. This diversity of applications opens a large range of research where chemistry, as a central science, overlaps the fields of physics, engineering, medicine, etc., generating a huge amount of knowledge and technological products used for humanity. This review article aimed at discussing some families of glasses, illustrating some applications. Due to the extension of the theme, and all points raised, we thought it would be good to divide the article into two parts. In the first part we focus on the properties of heavy metal oxide glasses, fluoride glasses and chalcogenide glasses. In the second part we emphasize the properties of glassy thin films prepared by sol-gel methodology and some applications, of both glasses as the films in photonics, and more attention was given to the nonlinear properties and uses of photonic fibers. Univ Estadual Paulista, Inst Quim, CP 355, BR-14800060 Araraquara, SP, Brazil Univ Sao Paulo, Fac Filosofia Ciencias & Letras Ribeirao Preto, Dept Quim, BR-14040901 Ribeirao Preto, SP, Brazil Univ Fed Alfenas, Inst Ciencia & Tecnol, Campus Pocos De Caldas, BR-37715400 Pocos De Caldas, MG, Brazil Univ Presbiteriana Mackenzie, BR-01302907 Sao Paulo, SP, Brazil Univ Sao Paulo, Inst Fis Sao Carlos, BR-13566590 Sao Carlos, SP, Brazil Univ Fed Pernambuco, Dept Quim, BR-50740560 Recife, PE, Brazil Univ Laval, Ctr Opt Photon & Laser, Quebec City, PQ G1K 7P4, Canada Univ Estadual Paulista, Inst Quim, CP 355, BR-14800060 Araraquara, SP, Brazil

Made available in DSpace on 2018-11-26T17:55:51Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-04-01. Added 1 bitstream(s) on 2021-07-15T14:32:24Z : No. of bitstreams: 1 S0100-40422016000300340.pdf: 4072751 bytes, checksum: 635ad996b95ebc83868fbdbb081d0bae (MD5) In this second part it will be discussed some photonic applications of glassy and glass ceramic thin films which can be used as planar waveguides. Some photonic applications require certain specifications of glass, which can be quantified by studying the nonlinear optical properties of the materials. Therefore, a brief introduction of these phenomena is discussed, as well as the use of femtosecond lasers to manipulate the composition or for the preparation of waveguides into glasses. Finally, the article will address a brief introduction on microstructured optical fibers and commercial application prospects for these devices. Univ Estadual Paulista, Inst Quim, CP 355, BR-14800060 Araraquara, SP, Brazil Univ Sao Paulo, Fac Filosofia Ciencias & Letras Ribeirao Preto, Dept Quim, BR-14040901 Ribeirao Preto, SP, Brazil Univ Fed Alfenas, Inst Ciencia & Tecnol, Campus Pocos De Caldas, BR-37715400 Pocos De Caldas, MG, Brazil Univ Presbiteriana Mackenzie, BR-01302907 Sao Paulo, SP, Brazil Univ Sao Paulo, Inst Fis Sao Carlos, BR-13566590 Sao Carlos, SP, Brazil Univ Fed Pernambuco, Dept Quim, BR-50740560 Recife, PE, Brazil Univ Laval, Ctr Opt Photon & Laser, Quebec City, PQ G1K 7P4, Canada Univ Estadual Paulista, Inst Quim, CP 355, BR-14800060 Araraquara, SP, Brazil

Crystalline lead–pyrophosphate precursor was prepared in aqueous solution from lead nitrate and phosphoric acid and characterized by X-ray diffraction, thermogravimetry and Raman scattering. This crystalline lead–phosphate was then used to prepare glass samples in the binary system Pb 2 P 2 O 7 –WO 3 . Dependence of WO 3 content on thermal, structural and optical properties were investigated by thermal analysis (DSC), Raman spectroscopy, UV–visible and near-infrared absorption and M-Line technique to access refractive index values. Incorporation of WO 3 in the lead–pyrophosphate matrix enhances the glass transition temperature and thermal stability against devitrification, favors formation of P O W bonds and WO 6 clusters. In addition, optical properties are strongly modified with a redshift of the optical bandgap with WO 3 incorporation as well as an increase of the refractive index from 1.89 to 2.05 in the visible.

Glasses were prepared by the melt-quenching method in the ternary system Pb(PO 3 ) 2 -WO 3 -PbF 2 and doped with Er 3+ in order to prepare luminescent transparent glass-ceramics. This work focused on thermal and structural characterization of tungsten lead-phosphate glasses and crystallization study for preparing transparent glass-ceramics. Thermal properties such as thermal stability and crystallization behavior upon heating were investigated by DSC in function of PbF 2 content. For low PbF 2 concentrations, only one crystallization peak due to Pb 3 (PO 4 ) 2 is observed whereas samples containing more than 15% of PbF 2 present another exothermic event at lower temperatures related with precipitation of PbF 2 , Pb 2 P 2 O 7 and Pb 2 OF 2 . Structural investigations by Raman spectroscopy suggest that PbF 2 modifies the tungsten-phosphate network through the formation of P―F and P―O―Pb bonds but the average network connectivity remains almost constant. A crystallization study has been performed by DSC to investigate the dominant crystallization mechanisms in these glasses and it has been established that Pb 3 (PO 4 ) 2 is nucleated on the surface whereas PbF 2 , Pb 2 P 2 O 7 and Pb 2 OF 2 crystallize dominantly from the glassy bulk. Transparent glass-ceramics containing nanosized PbF 2 crystallites were also prepared by suitable heat-treatment on the glass sample containing 20% of PbF 2 and Raman microscopy of these glass-ceramics supports the crystallization mechanisms determined by DSC.

Glasses were prepared in the pseudo-binary system (1 − x)AgPO3–xWO3 (0≤ × ≤ 0.6 mol%). The structural evolution of the vitreous network was studied as a function of composition by thermal analysis, Fourier Transform Infrared spectroscopy (FTIR), Raman scattering, high resolution 31P solid state NMR and XANES at the W-L1 absorption edge. For compositions with x ranging from 0 to 0.5 a pronounced increase in the glass transition temperature is observed, suggesting a significant increase in the glass network connectivity. At the same time Raman spectra indicate that tungsten atoms are linked to non-bridging oxygen atoms (W–O- or W=O bonded species) whereas the 31P MAS-NMR spectra indicate the successive formation of new P–O–W linkages. The formation of some anionic tungsten sites (if these are revealed by the presence of W–O terminal bonds) implies an increase in the average degree of polymerization of the phosphate network, which is consistent with the compositional evolution of the 31P MAS-NMR spectra at low x values. For higher x-values, the Raman spectra indicate the presence of W–O–W linkages. W-L1 XANES data indicate that at least 90% of tungsten atoms are octahedrally coordinated.

Glasses were prepared in the binary system (100 − x )NaPO 3 – x MoO 3 with x varying from 0 to 50 mol%. An increase in the MoO 3 concentration promotes a strong absorption in the visible and near infrared attributed to Mo reduction during glass synthesis. X-ray absorption measurements were performed at the Mo K and L 3 edges to investigate both the coordination number and oxidation state of Mo in these glasses. The evolution of the pre-peak observed at the K edge suggests that Mo atoms are six-fold coordinated in these glasses. This hypothesis was confirmed by data obtained at the Mo–L 3 -absorption edge. Since the final electronic states at the L 3 -absorption edge are mostly orbitals of d-character which are splitted by the ligand field, the amplitude of the d-orbital splitting could be estimated and the related coordination number of Mo obtained. Finally, the oxidation state of Mo could be related with a change of the white line intensity at the Mo–L 3 edge. These results confirm that the optical absorption in the visible is due to Mo reduction and that transparent samples prepared by slow cooling contain less reduced Mo species.

Vitreous samples were prepared in the binary system NaPO 3 –MoO 3 and their characteristic temperatures were determined by Differential Scanning Calorimetry. Glasses with high amounts of MoO 3 (>45 mol%) exhibit an intense crystallization peak and the composition 50 NaPO 3 –50 MoO 3 was chosen for the crystallization study. Two different methods based on thermal analyzes were used to determine the mechanism of crystallization in these molybdenum–phosphate glasses. In the first procedure, thermal analyses by DTA were performed on samples with different grain sizes and the crystallization tendency deduced in function of superficial area. The second method used the classical non-isothermal crystallization study: DSC measurements were performed under several heating rates to access activation energy for crystallization and Avrami parameter n . Critical cooling rate was calculated and compared with experimental data obtained from DTA analysis upon cooling.

Tungstate fluorophosphate glass compositions with high WO3 concentration were prepared in the ternary system (80−0.8x)NaPO3–(20−0.2x)BaF2–xWO3 with x = 40,50 and 60 mol%. Transparency decreases as WO3 concentration increases but can be improved by addition of oxidizing systems such as CeO2 or Sb2O3/NaNO3. Characterizations by thermal analysis (DSC) point out that an increase in the amount of WO3 results in a higher glass transition temperature. In addition, such compositions are very stable against devitrification since samples containing 40% and 50% of WO3 donot even exhibit the expected crystallization event. In these samples, the stability against crystallization decreases with the WO3 content and vitreous sample containing 60% of WO3 exhibits an endothermic event around 620 °C due to crystallization of monoclinic WO3 phase. In these glasses, it was shown that the nucleation stage can be induced by thermal-treatment when external nucleating agents such as Ti or Sb are used. Finally, gold-doped samples exhibit a higher crystallization tendency and monoclinic WO3 phase can be grown in such glasses.

Erbium-doped organic-inorganic hybrids derived from different carboxylic acids (acetic, formic, and valeric) solvolysis have been prepared and characterized. The hybrid matrix (named as diureasil) is composed of a siliceous network grafted to both ends of a polymer chain containing about 8.5 oxyethylene units. Er3 + ions have been incorporated as erbium triflate salt, Er(CF 3 SO 3 ) 3 , with n = 5, 10, and 20, where n denotes the ratio of (OCH 2 CH 2 ) moieties of the hybrid organic counterpart per Er 3+ ion. Characterization techniques include X-ray absorption (EXAFS) at the Er L III -edge, Fourier transform infrared spectroscopy (FT-IR) and photoluminescence. FT-IR studies reveal that both free and coordinated triflate ions exist in the hybrids, independently of the carboxylic acid used. Moreover, the "amide I" and "amide II" infrared spectral regions are deeply affected suggesting that the Er 3+ ions interact with the carbonyl groups of the diureasil matrix. EXAFS results show that the Er 3+ first coordination shell is composed by 10-11 oxygen atoms at an average distance of 2.30-2.32 A. The Ωλ (λ = 2,4,6) intensity parameters were evaluated from absorption measurements together with the Er 3+ 4 I 13/2 state radiative lifetime (TRAD) and the peak emission cross section (σ EM ). Values obtained were Ω 2 = 12.3 x 10- 20 cm 2 , Ω 4 = 5.56 x 10- 20 cm 2 and Ω 6 = 3.56 x 10- 20 cm 2 , TRAD = 3.6 ms and σ EM (1537 nm) = 1.0 x 10- 20 cm 2 . The host characteristic broad emission band in the visible and the Er 3+ emission at 1.5 μm were discerned. Bandwidth of ∼78 nm is observed for the latter emission which, together with the QA, TRAD, and σ EM spectroscopic parameters, denote the potential application of these hybrids in optical amplification devices.

Planar waveguides were prepared by Ag + /K + ↔ Na + ion-exchange on Er +3 -doped GeO 2 –ZnO–Na 2 O–Li 2 O glasses obtained by a melting–casting method. Optical parameters of the waveguides were measured at 543.5, 632.8, and 1550 nm by m-line technique as a function of the Ag + ion-exchange time. The optimized planar waveguides show an effective diffusion depth ( d ) of 2.95 μm and well confined propagating TE 0 and TM 0 modes at 1550 nm. Spectroscopic properties as photoluminescence emission and emission decay time were evaluated for the erbium-doped planar waveguide, indicating that Ag + ↔ Na + ion-exchange enhance the photoluminescence emissions in the green and infrared regions from erbium ions. The glass system studied is promising to be applied as optical amplifiers in the C-telecom band. Green emission sensitized by Ag + was also observed.

Thin films were prepared using glass precursors obtained in the ternary system NaPO 3 BaF 2 WO 3 and the binary system NaPO 3 WO 3 with high concentrations of WO 3 (above 40% molar). Vitreous samples have been used as a target to prepare thin films. Such films were deposited using the electron beam evaporation method onto soda-lime glass substrates. Several structural characterizations were performed by Raman spectroscopy and X-ray Absorption Near Edge Spectroscopy (XANES) at the tungsten L I and L III absorption edges. XANES investigations showed that tungsten atoms are only sixfold coordinated (octahedral WO 6 ) and that these films are free of tungstate tetrahedral units (WO 4 ). In addition, Raman spectroscopy allowed identifying a break in the linear phosphate chains as the amount of WO 3 increases and the formation of P O W bonds in the films network indicating the intermediary behavior of WO 6 octahedra in the film network. Based on XANES data, we suggested a new attribution of several Raman absorption bands which allowed identifying the presence of W O − and W O terminal bonds and a progressive apparition of W O W bridging bonds for the most WO 3 concentrated samples (above 40% molar) attributed to the formation of WO 6 clusters.

Vitreous samples containing high concentrations of WO 3 (above 40% M) have been used as a target to prepare thin films. Such films were deposited using the electron beam evaporation method onto soda-lime glass substrates. These films were characterized by X-ray diffraction (XRD), perfilometry, X-ray energy dispersion spectroscopy (EDS), M-Lines and UV–vis absorption spectroscopy. In this work, experimental parameters were established to obtain stable thin films showing a chemical composition close to the glass precursor composition and with a high concentration of WO 3 . These amorphous thin films of about 4 μm in thickness exhibit a deep blue coloration but they can be bleached by thermal treatment near the glass transition temperature. Such bleached films show several guided modes in the visible region and have a high refractive index. Controlled crystallization was realized and thus it was possible to obtain WO 3 microcrystals in the amorphous phase.

Glasses in the binary system (100 x)SbPO4–xWO3 (20 6 x 6 60, x in mol%) have been prepared and characterized. Differential thermal analysis (DTA) shows that the glass transition temperature, Tg, increases from 412 � C, for samples containing 20 mol% of WO3, to 481 � C observed for glass containing 60 mol%. Sample containing 40 mol% in WO3 were observed to be the most stable against devitrification. The structural organization of the glasses has been studied by using Fourier transform infra-red (FTIR), Raman, 31 P Magic angle spinning (MAS) and spin echo nuclear magnetic resonance (NMR) spectroscopies. Results suggest two distinct networks comprising the glass structure, one with high SbPO4 content and the other characteristic of the highest WO3 content samples. The glasses present photochromic properties. Colour changes are observed for samples after exposure to ultraviolet or visible laser light. XANES, at L1 absorption edge of tungsten, suggests partial reduction from W 6+ to W 5+ species during the laser irradiation. The photochromic effects and the colour changes, promoted by laser excitation, are reversible and easily removed by heat for during 1 h at 150 � C. Subsequent ‘write/erase’ cycles can be done without degradation of the glasses. � 2007 Elsevier B.V. All rights reserved. PACS: 61.43.Fs; 61.66.Fn; 82.47.Jk

Vitreous samples were prepared in the NaPO3–BaF2–WO3 ternary system with high WO3 concentrations. These glasses exhibit a strong absorption in the visible due to the presence of reduced tungsten species and the use of oxidizing species is required. The couple Sb2O3/NaNO3 was introduced in the composition and allowed to obtain transparent glasses. These oxidized samples were illuminated by visible laser radiation and showed an efficient volumetric photochromic effect. The photosensitive effect appeared as a dark spot throughout the entire volume of the glasses. The effect was investigated by several techniques such as, UV-visible absorption, Raman and XANES at the L1 and L3 tungsten absorption edges. The results suggest a photoreduction of tungsten atoms without structural changes of the viteous network. Finally, the photochromic effect can be erased by thermal treatment at 200 °C for a few minutes.

Functionalized elastomeric networks were obtained via a polycondensation reaction between poly(dimethylsiloxane) (PDMS) containing Si(CH3)2OH as end groups and an imidazole- or benzimidazole-modified alkoxysilane. The structure of the polymeric materials was characterized via attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and solid-state 13C and 29Si NMR spectroscopy, which indicated the presence of silsesquioxane units that acted as nodes on the PDMS chains and linked the functional groups. Thermogravimetric analysis (TGA) of the product indicated high thermal stability with an initial weight-loss temperature around 450 K. The capacity for the removal of copper(II) from aqueous solution was estimated from adsorption isotherms, yielding values of 35.74 and 66.09 mg g-1, respectively, for benzimidazole-and imidazole-functionalized materials. The major adsorption models were evaluated to fit the removal data of copper(II) and the model elaborated by Sips was determined to provide the best fit for both prepared materials.

The glass forming ability was investigated in the codoped Er3+/Yb3+ ternary system NaPO3-WO3-PbF2 with increasing amounts of PbF2. It has been found that glass samples can be obtained for PbF2 contents ranging from 0 mole% to 50 mole% for the codoped samples and an undoped sample containing 60% of lead fluoride could also be vitrified. Thermal properties of the most PbF2 concentrated glasses exhibit strong dependence of the composition with a decrease of the glass transition temperatures and thermal stabilities against devitrification with increasing the lead fluoride content. These glass samples were heat-treated near the crystallization peaks and the X-ray diffraction measurements pointed out that the dominant phase which precipitates from the glass samples containing 40% and 50% of PbF2 is the lead fluorophosphate phase Pb5F(PO4)3 whereas the sample containing 60% of PbF2 exhibits a preferential bulk crystallization of cubic lead fluoride β-PbF2.

In this work, new glass compositions were prepared in the ternary system GeO2–K2O–Ta2O5. Potassium oxide was added to reach the complete melt of the starting mixture and two composition series were investigated: the first one with a constant K2O molar content of 10% in the ternary system (90–x)GeO2–10K2O–xTa2O5 and the second one with the same molar content of K2O and Ta2O5 in the ternary system (100–2x)GeO2–xK2O–xTa2O5. Homogeneous and transparent glasses could be obtained between x = 0 and 20. X-ray diffraction analyzes of samples with x = 25 identified orthorhombic Ta2O5 in the first series and an isostructure of K3.8Ge3Nb5O20.4 in the second series where it is assumed that Ta5+ ions are inserted in the Nb5+ sites. As one of our goal with these materials is related with the preparation of glass-ceramics containing Ta2O5 nanocrystals, the first series has been selected for further characterizations. An increase in glass-transition temperatures with increasing Ta2O5 content as well as an increase of the thermal stability from x = 0 to 10 has been identified by differential scanning calorimetry. For higher contents, crystallization events were identified. Fourier transform infrared and Raman spectroscopic characterizations allowed to point out the intermediary behavior of Ta2O5 in the vitreous network where TaO6 octahedra are inserted inside the germanate network with TaO6 clusters identified at higher Ta2O5 contents. Heat-treated samples with high tantalum contents (x = 15 and 20) exhibit preferential precipitation of orthorhombic Ta2O5 with nanometric size, suggesting the possibility of obtaining transparent glass-ceramics for optical applications.