Tungsten Phosphate Glasses Research Articles

Theoretical studies on the g-factors and the local structure of W5+ ions in tungsten phosphate glasses

In this work, we adopt the three-order perturbation formulae for g-factors (g//, g^) of d1 ions in the octahedral environment to calculate the g-factors of W5+ ions in tungsten phosphate glasses containing lithium (P2O5-Li2WO4-Li2O). In the light of the high valence state of the studied W5+ centers and hence the strong covalency of the studied octahedral [WO6]7- cluster, we consider the contributions to g-factors from the ligand orbital and spin-orbit (SO) coupling interactions based on the cluster approach. The required tetragonal crystal-field parameters are calculated from the local structure of W5+ ions based on the superposition model. According to the theoretical calculations, we find that the octahedral [WO6]7- clusters possess the tetragonally compressed distortion with a shorter W-O bond length (≈1.54 Å) and a longer one (≈2.26 Å) along C4 axis and four normal W-O bond length (≈1.94 Å) in the perpendicular plane, which infers that the W5+ ions are in the form of tungstyl ions (i.e., WO3-). Based on the local structural data, the theoretical values of g// and g^ agree well with the experimental values.

Structural and optical characterization of tungsten phosphate glasses containing silver and erbium

Tungsten-phosphate glasses with up to 20 mol% of silver chloride content were prepared using the conventional melt-quenching method. Ag nanoparticles (AgNPs) formation was achieved by nucleation and growth using controlled thermal treatment. Thermal properties and the local structure were studied as a function of Ag content by means of DSC, Raman and 31P MAS NMR spectroscopy. The Ag NP growth was monitored by real-time UV–Vis spectroscopy and confirmed by TEM. The optical linear and nonlinear properties were evaluated as a function of the AgNPs growth. NIR emission of Er3+ ions was studied and showed a strong dependence on the AgNPs size. A weak luminescent enhancement occurs when small AgNPs are present, but on the other hand, a strong quenching takes place in the presence of larger AgNPs, due to the local field effect mediated by surface plasmon resonance (SPR) and Er3+ intersystem crossing processes, respectively. A stronger luminescence suppression by excitation at 545 nm was assigned to the increased contribution to back-energy transfer from Er3+ to AgNPs and re-absorption by SPR. These results highlight the importance of a careful study of the relation between noble metal NPs size and the excitation wavelength to increase the efficiency of the future photonic devices, such as NIR solid state laser, Kerr effect-based laser or amplifiers.

Promising Tb3+-doped gallium tungsten-phosphate glass scintillator: Spectroscopy, energy transfer and UV/X-ray sensing

Undoped and Tb3+-doped (0.5–10 mol%) gallium tungsten-phosphate glasses, in the new compositional system NaPO3-Ga2O3-Na2WO4, were prepared and characterized by UV–visible absorption, photoluminescence excitation and emission, excited state decay measurements and X-ray excited radioluminescence measurements. A detailed study of ion-ion energy transfer, based on the analysis of decay curves by the Inokuti-Hirayama model, indicated that the energy transfer process affecting the emitting level 5D3 of Tb3+ is related to dipole–dipole interaction. Additionally, a theoretical model was successfully employed to establish a correlation between the emission color variation due to changes in the green to blue emission ratio (IG/IB). The emission spectra of the undoped and Tb3+-doped glasses were measured under UV and X-ray excitation. From the viewpoint of UV-sensing, samples doped with up to 7.0 mol% Tb3+ do not present visible emission quenching, whereas X-ray sensing is not prone to quenching at all up to 10 mol% Tb3+ doping. These characteristics, associated to a relatively high density, highlight the potential of these glasses as X-ray scintillators.

Reversible 3D optical data storage and information encryption in photo-modulated transparent glass medium

Transparent glass has been identified as a vital medium for three-dimensional (3D) optical information storage and multi-level encryption. However, it has remained a challenge for directly writing 3D patterning inside a transparent glass using semiconductor blue laser instead of high-cost femtosecond laser. Here, we demonstrate that rare earth ions doped transparent glass can be used as 3D optical information storage and data encryption medium based on their reversible transmittance and photoluminescence manipulation. The color of tungsten phosphate glass doped with rare earth ions change reversibly from light yellow to blue upon alternating 473 nm laser illumination and temperature stimulation, resulting in the reversible luminescence modulation. The information data could be repeatedly written and erased in arbitrary 3D space of transparent glass, not only showing the ability of the excellent reproducibility and storage capacity, but also opening opportunities in information security. The present work expands the application fields of luminescent glass, and it is conducive to develop a novel 3D data storage and information encryption media.

Effect of silver and antimony on optical properties of tungsten-phosphate glasses

The effect of silver ions on the photochromic properties of tungsten phosphate glass is investigated. All samples when excited at 377 nm exhibit ~430 nm luminescence attributed to the charge transfer mechanism within the WO42−tungstate anions. The broad absorption band extending from ultraviolet to the visible region, between 500 and 1400 nm, of the NaPO3-WO3 (PW) base matrix due to the small-polarons(Wx5+W1−x6+O3) transferring charges between neighboring tungsten ions according to the following photon absorptionWA5++WB6++hvs→WA6++WB5+. The dual oxidation state of the antimony, Sb3+ and Sb5+, incorporated into the matrix at the 0.5−xNaPO3−0.5WO3−xSb2O3x=0…0.2mol% (PWS) ratio acts as a reducing element of the W5+ ions leading to the suppression of polarons as UV-VIS absorption centers. These results are confirmed by EPR measurements with scanned magnetic field between 2500 and 4500G. The most intense effect is observed for nominal doping aboveAgNO3≥10mol%. The temporal dynamics of luminescence at ~430 nm as a function of UV exposure time shows that both,Wx5+W1−x6+O3 for PW glasses as well as Ag+ for PWSA glasses act as traps for the charge generated by the excitedWO42− anions. Photodarkening due to continuous exposure to UV radiation reduces the pump transmission by ~12% of its initial value for PW and PWSA glasses. This is attributed to F-center formation (Ag+) which acts traps to the photoexcited electrons. This is attributed to oxidation of silver ions (Ag+) becoming metallic silver (Ag0). The effect when compared to PWS glass was observed to be reduced by only 2% over the same interval under the same pumping conditions.

Tungsten sodium phosphate glasses doped with trivalent rare earth ions (Eu3+, Tb3+, Nd3+ and Er3+) for visible and near-infrared applications

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.

Conductivity features of semiconducting tungsten‐phosphate glasses

The ac conductivity of 70WO3–30P2O5 glass composition prepared by melt quenching was first studied in the temperature range 25°C to 350°C. The conductivity of the semiconducting glass is investigated with various electrodes (Pt and Ga-Ag alloy). It is shown that the type of spectrum of cell impedance depends on the chosen electrodes. The influence of the samples geometry on the conduction is established. The influence of gas atmosphere (argon, oxygen, and air of different humidity) on electrical conductivity of tungsten-phosphate glass on is studied for the first time. A mixed electronic-ionic conductivity in the 70WO3–30P2O5 glass is found out. The transport numbers are shown as a function of temperature. Ionic and electronic contribution to the conduction is estimated. The electrical conductivity of glass undergoes changes from 8.6 × 10−8 (25°C) to 3.1 × 10−4 S/cm (300°C) in air.

Conductivity Studies of Glasses in the System WO3−P2O5

Quenching method was used to obtain glasses in the system xWO3-(100-x)P2O5 (x = 70, 75, 80, 82 mol %). The electrical conductivity of the compositions was examined by a set of electrochemical techniques: impedance spectroscopy, pulse method, and dc method with different electrodes in the temperature range 25–320°C. It was shown that tungsten phosphate glasses are mostly electronic conductors possessing semiconducting properties. It was found that the electrical conductivity of the glasses grows with increasing content of tungsten oxide. The highest conductivity at room temperature (6.7 × 10-7 S cm−1) is observed for the composition 82WO3-18P2O5.

Synthesis of Tungsten Phosphate Glasses and Study of Their Thermal Properties

xWO3–(100–x)P2O5 (70 mol % ≤ x ≤ 82 mol %) glasses were obtained by melt quenching. Their thermal properties were studied by the DTA method. It was found that the rise of WO3 сontent leads to a decrease in thermal stability of glasses and lower glass transition and crystallization temperatures. The compositions 70WO3–30P2O5 and 75WO3–25P2O5 are not crystallized in the temperature range 35–950°C.

Luminescence quenching versus enhancement in WO3-NaPO3 glasses doped with trivalent rare earth ions and containing silver nanoparticles

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.

Effect of lead fluoride incorporation on the structure and luminescence properties of tungsten sodium phosphate glasses

Tungsten phosphate glasses are known to be promising materials for several applications in optics such as non linear optical properties, lower phonon energy or photochromic effects related with tungsten oxide incorporation inside the phosphate network. In this study, lead fluoride has been incorporated in a 60NaPO3–40WO3 glass composition according to the ternary molar compositions (100−x)[0.6NaPO3–0.4WO3]–xPbF2 with x varying from 0 to 60mol%. The structural changes as a function of composition were investigated by thermal analysis, UV–visible absorption, Raman spectroscopy, X-ray diffraction of the crystallized samples, and Eu3+ emission in the visible. While DSC analyzes points out a strong decrease in the glass network connectivity and higher crystallization tendency with increasing PbF2 contents, Raman spectra clearly identify a progressive incorporation of PbF2 in the phosphate network with the formation of terminal PF and WF bonds. These results are also in agreement with the crystallization of β-PbF2 observed for the most lead fluoride concentrated samples. Investigation of Eu3+ emission data in the visible showed longer 5D0 excited state lifetime values and higher quantum efficiencies. These results are discussed in terms of the assumption of higher local symmetry around Eu3+ with increasing PbF2 contents.

Structural and spectroscopic characteristics of Eu3+-doped tungsten phosphate glasses

Tungsten based phosphate glasses are interesting non-crystalline materials, commonly known for photochromic and electrochromic effects, but also promising hosts for luminescent trivalent rare earth ions. Despite very few reports in the literature, association of the host́s functionalities with the efficient emissions of the dopant ions in the visible and near-infrared spectra could lead to novel applications. This work reports the preparation and characterization of glasses with the new composition 4(Sb2O3)96−x(50WO3 50NaPO3)xEu2O3 where x=0, 0.1, 0.25, 0.5 and 1.0mol%, obtained by the melt quenching technique. The glasses present large density (∼4.6gcm−3), high glass transition temperature (∼480°C) and high thermal stability against crystallization. Upon excitation at 464nm, the characteristic emissions of Eu3+ ions in the red spectral region are observed with high intensity. The Judd–Ofelt intensity parameters Ω2=6.86×10−20, Ω4=3.22×10−20 and Ω6=8.2×10−20cm2 were calculated from the emission spectra and found to be higher than those reported for other phosphate glass compositions. An average excited state lifetime value of 1.2ms, was determined by fitting the luminescence decay curves with single exponential functions and it is comparable or higher than those of other oxide glasses.

Optically-transparent and electrically-conductive AgI–AgPO3–WO3 glass fibers

We report the fabrication, characterization, and fiber drawing of a silver iodide tungsten-phosphate glass that conducts both light and electricity efficiently.

Proton conducting tungsten phosphate glass and its application in intermediate temperature fuel cells

Abstract High concentrations of proton carriers (5.0 × 10 21 cm − 3 ) were injected into tungsten phosphate glass (8WO 3 -35NaO 1/2 -8NbO 5/2 -5LaO 3/2 -44PO 5/2 ) by electrochemical substitution of sodium ions with protons at 345 °C. The electromotive force of a hydrogen concentration cell that used the substituted glass as a solid electrolyte indicated a mixed conduction of protons and electrons in the glass with a mean proton transport number of 0.8 at 300 °C. The partial conductivity of the protons was 8.0 × 10 − 4 Scm − 1 . The fuel cell generated electricity at a maximum power density of 1.3 mWcm − 2 , even though its open circuit voltage was only 0.77 V because of the electronic contribution to the conductivity. Methods to increase the proton conductivity for improving fuel cell performance are discussed.

Electrochemical Substitution of Sodium Ions in Tungsten Phosphate Glass with Protons

A novel technique was developed to inject proton carriers into phosphate glass. Sodium ions in the sodium tungsten phosphate glass were electrochemically substituted with protons. A glass plate with a deposited Pd anode was placed on the molten tin cathode and heated at a temperature below glass transition temperature under DC-bias in hydrogen containing atmosphere. Protons were injected from the palladium anode and substituted the sodium ions in the glass. The sodium ions migrated to the cathode and discharged to the molten tin cathode by capturing an electron from the external circuit. The atomic sodium dissolved into the cathode and reacted with CO2 impurities in the atmosphere resulting deposition of sodium carbonate on the tin cathode surface. After almost all of the sodium ions were discharged from the glass, the proton concentration in the glass reached 4.3 × 1021 cm−3. The proton conductivity was found to be 1 × 10−3 Scm−1 at 350°C. The injected protons were stable at temperatures below 400°C. The glass obtained by this technique behaves as a mixed conductor of protons and electrons with a proton transport number of 0.30. A possible means to suppress the electronic conductivity was discussed.

The Role of Bi2O3 on the Thermal, Structural, and Optical Properties of Tungsten-Phosphate Glasses

Glasses in the ternary system (70 - x)NaPO(3)-30WO(3)-xBi(2)O(3), with x = 0-30 mol %, were prepared by the conventional melt-quenching technique. X-ray diffraction (XRD) measurements were performed to confirm the noncrystalline nature of the samples. The influence of the Bi(2)O(3) on the thermal, structural, and optical properties was investigated. Differential scanning calorimetry analysis showed that the glass transition temperature, T(g), increases from 405 to 440 °C for 0 ≤ x ≤ 15 mol % and decreases to 417 °C for x = 30 mol %. The thermal stability against devitrification decreases from 156 to 67 °C with the increase of the Bi(2)O(3) content. The structural modifications were studied by Raman scattering, showing a bismuth insertion into the phosphate chains by Bi-O-P linkage. Furthermore, up to 15 mol % of Bi(2)O(3) formation of BiO(6) clusters is observed, associated with Bi-O-Bi linkage, resulting in a progressive break of the linear phosphate chains that leads to orthophosphate Q(0) units. The linear refractive index, n(0), was measured using the prism-coupler technique at 532, 633, and 1550 nm, whereas the nonlinear (NL) refractive index, n(2) was measured at 1064 nm using the Z-scan technique. Values of 1.58 ≤ n(0) ≤ 1.88, n(2) ≥ 10(-15) cm(2)/W and NL absorption coefficient, α(2) ≤ 0.01 cm/GW, were determined. The linear and NL refractive indices increase with the increase of the Bi(2)O(3) concentration. The large values of n(0) and n(2), as well as the very small α(2), indicate that these materials have large potential for all-optical switching applications in the near-infrared.

Porous shell/dense core structures prepared in tungsten phosphate glass through template-free route

The preparation of the 11.7Li 2O–39.7WO 3–10.9CaO–37.7P 2O 5 glass (pgLWCP) was based on a one-step heat treatment of the 6Li 2O–18WO 3–43CaO–33P 2O 5 (gLWCP) glass followed by leaching of the β-Ca 2P 2O 7 phase formed during the crystallization process. The porous structure was formed in the region formerly occupied by the β-Ca 2P 2O 7 phase. The gLWCP undergoes devitrification through surface crystallization. This process occurs after a thermal treatment in lower temperature and in a shorter period of time than that required for the complete crystallization. After acid leaching treatment, we obtained a core-/shell-like structure with a very well-defined dense glass (gLWCP)/porous glass (pgLWCP) interface. The pgLWCP exhibits reversible coloration–decoloration reactions.

Mixed Conduction of Proton and Electron in Tungsten Phosphate Glass and its Hydrogen Transport

The transference number of protons and the hydrogen transport behavior through tungsten phosphate glass have been measured through the use of a concentration cell. Based on measurement of the electrical motive force by changing the hydrogen partial pressure of both sides of a specimen glass kept in the concentration cell, the ionic transference number was estimated to be 48%. When one side is kept in hydrogen and the other in nitrogen, hydrogen transport is observed and its quantity is accelerated by applying a positive dc bias on the hydrogen side. After applying the dc bias continuously for over 1 h, the hydrogen transport is abruptly increased with no cracks and the hydrogen flux is 1.510-3 molcm-2s-1.

Oxide Glass/Amorphous Metal Alloy Laminated Membrane for Hydrogen Separation

Abstract A five-layered membrane composed of an amorphous Ni–Nb–Zr alloy substrate (ca. 30 μm), thin proton–electron mixed conductive tungsten phosphate glass films (ca. 50 nm) and Ni coatings (ca. 20 nm) was fabricated by pulsed laser deposition and vacuum evaporation. A flux of hydrogen passed through the laminated membrane without Pd at 673 K at ca. 2×10−6 mol·cm−2·s−1, and no degradation was observed in the 10 h operation. The present results suggest that amorphous Ni–Nb–Zr alloy passivated with WO3-based oxide glass is a promising material for H2 filtering in a medium temperature range.

Hydrogen permeation of tungsten phosphate glass thin films

Thin films of tungsten phosphate glasses were deposited on a Pd substrate by a pulsed laser deposition method and the flux of hydrogen passed thorough the glass film was measured with a conventional gas permeation technique in the temperature range 300–500 °C. The glass film deposited at low oxygen pressure was inappropriate for hydrogen permeation because of reduction of W ions due to oxygen deficiency. The membrane used in the hydrogen permeation experiment was a 3-layered membrane and consisted of Pd film (~ 20 nm), the glass film (≤ 300 nm) and the Pd substrate (250 µm). When the pressure difference of hydrogen and thickness of the glass layer were respectively 0.2 MPa and ~ 100 nm, the permeation rate through the membrane was 2.0 × 10 − 6 mol cm − 2 s − 1 at 500 °C. It was confirmed that the protonic and electronic mixed conducting glass thin film show high hydrogen permeation rate.