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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.

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.

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.

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 2018-11-28T15:26:08Z (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.

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.

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.

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.

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.

Changes occurring in absorption coefficients when glasses in the SbPO 4 –WO 3 binary system were irradiated by light, at the edge of the absorption band, were measured in real time. These glasses present good thermal and optical properties and photoinduced changes in the absorption coefficients are reversible by heat treatment around 150 °C. Subsequent recording/erasing cycles could be made without sample degradation. The sensitivity of the induced optical changes was studied for different wavelengths, light powers and energy of light dose exposures, and for different compositions of the glasses. The changes in the absorption coefficients of the glass samples were accompanied by a color change from yellow to blue, and were also characterized by visible spectroscopy. The color changes occurred through the entire volume of the glass (∼2 mm thickness) for the Ar-ion laser lines at the edge of the absorption band.

X-ray absorption spectroscopy was used to study the local environment of tungsten atoms in NaPO 3 –BaF 2 –WO 3 glasses and the results were compared with crystalline references Na 2 WO 4 and WO 3 . XANES measurements at the W-L 1 edge allowed to determine a distorted octahedral environment of tungsten atoms in these glasses similar to the local order of tungsten in monoclinic WO 3 . Extended X-ray absorption fine structure (EXAFS) has been used as a local probe to monitor the effect of WO 3 concentration on the tungsten environment. Based on an analysis of the EXAFS data, we proposed a three-shell model of oxygen atoms around tungsten as in monoclinic WO 3 . With increasing WO 3 concentration, it was found that R 2 decreases from 1.96 to 1.92 A whereas R 3 increases from 2.07 to 2.12 A.

Transparent glasses were synthesized in the NaPO3–BaF2–WO3 ternary system and several structural characterizations were performed by X-ray absorption spectroscopy (XANES) at the tungsten LI and LIII absorption edges and by Raman spectroscopy. Special attention was paid to the coordination state of tungsten atoms in the vitreous network. XANES investigations showed that tungsten atoms are only six-fold coordinated (octahedra WO6) and that these glasses are free of tungstate tetrahedra (WO4). In addition, Raman spectroscopy allowed to identify a break in the linear phosphate chains as the amount of WO3 increases and the formation of P–O–W bonds in the vitreous network indicating the modifier behavior of WO6 octahedra in the glass network. Based on XANES data, we suggested a new attribution of several Raman absorption bands which allowed to identify the presence of W–O− and WO terminal bonds and a progressive apparition of W–O–W bridging bonds for the most WO3 concentrated samples (⩾30% molar) due to the formation of WO6 clusters.

A new class of tungstate fluorophosphate glasses was identified in the NaPO 3 –BaF 2 –WO 3 ternary system. The variation of several physical properties was determined with respect to chemical composition. Characteristic temperatures, density and refractive index increase as tungsten oxide content increases. The optical transmission range and specially the energy bandgap depend of the WO 3 amount. No crystallization could be observed for the most WO 3 concentrated vitreous samples (⩾20% molar). Color and optical properties of the glasses depend of the melting time because of the presence of reduced tungsten species like W 5+ and W 4+ . In addition, photodarkening is observed in tungsten rich glass samples under UV laser illumination and this phenomenon can be reversible by heat treatment near the glass transition temperature.

This paper describes new glasses based on the Sb 2 O 3 -Cul association. The limits for glass formation have been investigated in four ternary systems: Sb 2 O 3 -CuI-NaCl, Sb 2 O 3 -CuI-NaI, Sb 2 O 3 -Cul-PbCl 2 and Sb 2 O 3 -CuI-Pbl 2 and bulk samples were prepared using 1 mol% As 2 O 3 as a stabilizer. Binary Sb 2 O 3 -CuI glasses require quenching to prevent crystallization. Ternary glasses are obtained by casting the liquid into a metal mold. Antimony oxide is the main glass component: its concentration lies between 50 and 90 mol%. Oxyiodide glasses appear less stable than oxychloride glasses. Chemical analysis does not show deviation from batch composition within errors of measurement. A limited volatilization of Sb 2 O 3 and PbCl 2 is likely to occur during synthesis. Glass transition temperature ranges between 250°C and 300°C. depending on composition. Density and thermal expansion coefficient have been measured for typical compositions. Refractive index is larger than 2. Optical transmission is limited by the optical band gap and by the multiphonon absorption. Infrared cut-off at 50% transmission is close to 6, 5 μm for a 3 mm thick sample. Main absorbing defects are OH groups and Si-O absorption around 5.5 μm. These impurities originate from processing. Scattering defects limit the optical quality of the samples. These defects are reduced using arsenic oxide as a fining additive.

In this work, tantalum alkali-phosphate glasses were prepared in the ternary system 0.9[(100 − x)NaPO3 − xTa2O5] − 0.1K2O with x varying from 0 to 20. The thermal properties as a function of Ta2O5 content were investigated by Differential Scanning Calorimetry and Differential Thermal Analysis in order to understand the influence of composition on glass transition temperatures and crystallization behaviors. Increasing Ta2O5 content leads to a drastic and linear increase of glass transition temperatures in agreement with the increasing viscosity of the melt observed during the synthesis. In addition, Ta2O5 incorporation results in high thermal stability against devitrification, suggesting the intermediary role of tantalum in the alkali-phosphate network. Comparison of powder and bulk thermal analyzes also pointed out a dominant surface crystallization mechanism for these glass samples. UV–visible absorption measurements proved the high visible transparency of the samples and a decrease of the optical bandgap energy with tantalum addition, suggesting an increase of the glass network covalency. Finally, vibrational spectroscopies performed by FTIR and Raman support the hypothesis of tantalum insertion inside the phosphate tetrahedral network with TaO6 units cross-linking the metaphosphate and pyrophosphate units. Thus, the intermediary behavior of tantalum increases the network connectivity with higher rigidity, glass transition temperatures and thermal stabilities against devitrification.