Infrared and Raman spectra of new molybdenum and tungsten oxyfluoride glasses

The infrared (400–1200 cm^–1) and Raman (200–1150 cm^–1) spectra are reported for the new AO₃-BaF₂-RF glasses where A is molybdenum or tungsten and RF is the alkali fluoride LiF, NaF and mixed LiF-NaF respectively. The observed absorption bands of each glass series were assigned to their vibrational modes. This study has shown that structural units formed in these glasses include [MoO₄] and [WO₄] tetrahedra, [MoO₆], [WO₆], [MoF₆] and [WF₆] octahedra groups.     

Gamma-ray dosimetric properties of molybdenum phosphate glasses

In the present work, a study of the temperature dependence of the d.c. electrical conductivity and conduction activation for a series of MoO₃-P₂O₃ glass systems has been carried out. The conductivity measurements of the unirradiated glass specimens proved to be mainly dependent on both temperature and transition metal ion content in the glass matrix. The results of the present investigation have shown that the conduction mechanism would be due to the electron exchange between the low and high valency states of the MoO₃ oxide (Mo" and Mo⁶⁺). The radiation-induced conductivity of the glass system studied, produced by gamma rays, has also been measured experimentally. The d.c. electrical conductivity has proved to be dose dependent, which showed a decrease with increasing -dose. The results reflect some evidence of the-ray dosimetric potential of the glass specimens studied.     

Framework influence of erbium doped oxyfluoride glasses on their optical properties

Glasses of different matrix (phosphate, borate, silicate and lead-silicate) were studied for their optical properties. The effect of Er dopant on transmittance and luminescence properties was presented. The significant “red shift” and “blue shift” of UV edge absorption were discussed based on the changes in the framework of the borate and phosphate glasses, respectively. It was showed that the integral intensity of the two main optical absorption transitions monotonically increases with the order: phosphate < borate < silicate < lead-silicate. Ellipsometric measurement was applied to obtain the refractive index of the glasses. The correlation between the shift of edge absorption and the change of refractive index was presented. Effect of glassy matrix on luminescence of Er³⁺ was discussed.     

Dielectric properties and polarizability of molybdenum tellurite glasses

The dielectric behaviour of the [TeO₂]_1–x [MoO₃] _x , x=0.2, 0.3 and 0.45 mol%, glassy system is reported for the temperature range 300–573 K and the frequency range of 0.1–10 kHz. Both the static and high frequency dielectric constants for these binary tellurite glasses decrease with increasing MoO₃ content. The temperature dependence of the dielectric constants of these glasses are positive. The frequency dependence of the dielectric constant identifies a frequency dependence which does not show a flattening at low frequency. The room temperature static dielectric polarizability is discussed in terms of the MoO₃ concentration. The temperature dependence of the dielectric constant has been analysed in terms of the temperature changes of both volume and polarizability and also a volume change of the polarizability.     

A study of the electrical properties of molybdenum phosphate glasses

A series of binary MoO₃-P₂O₅ and also ternary MoO₃-P₂O₅-In₂O₃ glasses were prepared and their electrical properties were investigated. The d.c. conductivity measurements show that the conduction in molybdenum phosphate glasses is by a hopping process in which the electrical charge transfers from Mo⁵⁺ to Mo⁶⁺ ion sites. The conductivity can be discussed in terms of the small polaron conduction mechanism. In contrast to vanadium phosphate glasses, the tunnelling term in the conductivity formula seems to make a significant contribution in molybdenum phosphate glasses and is associated with a hopping process in the non-adiabatic regime.     

掺Er~(3+)重金属氧氟锗酸盐玻璃光谱性质研究

研究了重金属氧氟锗酸盐玻璃中Er3+离子的吸收光谱、有效吸收和发射线宽、荧光光谱、荧光半高宽、荧光寿命、带宽特性和增益性能.应用Judd-Ofelt理论计算了Er3+离子的强度参数Ωt(t=2,4,6),应用McCumber计算了能级4I13/2→4I15/2跃迁的吸收和受激发射截面.结果显示,随PbF2含量增加,Er3+离子的强度参数Ω6,吸收线宽、发射线宽、荧光半高宽、荧光寿命、带宽特性和增益性能都增加.表明掺Er3+重金属氧氟锗酸盐玻璃可作为宽带光纤放大器潜在的基质材料.     

Thermal, structural and optical properties of new tungsten lead–pyrophosphate glasses

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 Pb₂P₂O₇–WO₃. Dependence of WO₃ 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 WO₃ in the lead–pyrophosphate matrix enhances the glass transition temperature and thermal stability against devitrification, favors formation of POW bonds and WO₆ clusters. In addition, optical properties are strongly modified with a redshift of the optical bandgap with WO₃ incorporation as well as an increase of the refractive index from 1.89 to 2.05 in the visible.     

Thermal and optical properties of zinc halotellurite glasses

Zinc halotellurite glasses were studied with respect to the glass transition, softening temperature, thermal expansion, optical energy gap, Urbach energy, density, molar volume, refractive index, polarizability, molar refraction and third order non-linear optical susceptibility. Thermal characteristic were determined using a dilatometry. The optical absorption in the wavelength range (300–3200 nm) was measured. From the absorption edge studies, the values of optical band gap (E _opt) and Urbach energy (ΔE) have been evaluated. Optical parameters viz., color dispersion, dispersion energy, E _d, average oscillator energy, E ₀, and third order non-linear optical susceptibility values are estimated from measuring the refractive index at different wavelength. Results obtained are discussed in terms of the glass structure.     

Thermal and optical properties of the Ga-Ge-Sb-Se glasses

A selected glass composition from the Ga-Ge-Sb-Se has been studied in detail for potential applications in the 8-12 μm region. The Ga₅Sb₁₀Ge₂₅Se₆₀ glass has a high enough glass transition temperature (283 °C), a relatively high refractive index (2.63 at 10 μm) and is very stable towards crystallization. An original purification method is developed to produce high purity glass with good transmission up to 15 μm. This glass is very resistant in normal environmental conditions and even in hot water (60 °C) during 24 h. It may be a good candidate for producing infrared components operating in the mid and far infrared region.     

Study of fluorine losses and spectroscopic properties of Er doped oxyfluoride silicate glasses and glass ceramics

The fluorine losses during synthesis of Er³⁺ doped transparent glasses in the SiO₂–PbO–PbF₂ system were investigated. The final fluorine contents of the glasses were detected by using a fluorine ion selective electrode. The results show that high fluorine losses are occured in the normal preparation processes. With the increase of initial PbF₂ contents or melting time resulted in the increase of the fluorine losses. The thermal and spectroscopic properties of the glasses and the corresponding glass ceramics were investigated through the analysis of the differential scanning calorimetry (DSC), absorption and upconversion luminescence spectra. The effects of fluorine contents show a decrease of the glass transition temperatures (Tg) of the glasses and an enhancement of upconversion intensity of the corresponding glass ceramics.     

Er-doped and Er, Yb co-doped oxyfluoride glasses and glass-ceramics, structural and optical properties

The selected glasses and glass-ceramics pertinent to following chemical composition in mol%:48%SiO₂-11%Al₂O₃-7%Na₂O-10%CaO-10%PbO-11%PbF₂-3%ErF₃ and 48%SiO₂-11%Al₂O₃-7%Na₂O-10%CaO-10%PbO-10%PbF₂-1%ErF₃-3%YbF₃ have been manufactured from high purity components (Aldrich) at 1450 °C in normal atmosphere. Glass optical fibers were successfully drawn. Subsequently they were subject to the heat-treatment at 700 °C in various time periods. The preceding differential thermal analysis (DTA) studies allowed estimating both the fiber drawing temperature and the controlled crystallization temperature of glass fibers. It has been observed that the controlled heat-treatment of oxyfluoride glass fibers results in the creation of Pb₅Al₃F₁₉, Er₄F₂O₁₁Si₃ and Er₃FO₁₀Si₃ crystalline phases. The identified phases were characterized by X-ray powder diffraction (XRD) and confirmed by selected area electron diffraction (SAED). The fibers consist of mixed amorphous-crystalline microstructure with nano-crystals of size even below 10 nm distributed in the glassy host. Their morphology was investigated applying high-resolution transmission electron microscopy. Optical properties and excited state relaxation dynamics of optically active ions (Er³⁺, Yb³⁺) in glass and glass-ceramics have been studied. Based on absorption spectra the Judd-Ofelt analysis was carried out. The main attention was directed to NIR luminescence at. 1.6 μm related to ⁴I_13/2 → ⁴I_15/2 Er³⁺ and less effective emission associated with ⁴I_11/2 → ⁴I_15/2 Er³⁺ and ²F_5/2 → ²F_7/2 Yb³⁺ transitions. The dissimilar spectroscopic properties have been revealed for glasses and glass-ceramic samples, respectively. The reduction of emission linewidth at 1.6 and 1.0 μm combined with substantial increase of ⁴I_13/2 lifetimes of erbium in glass-ceramics appear to be evidences that Er³⁺ ions are accommodated in crystalline phases. The structural and optical characteristics of oxyfluoride glass-ceramic fibers indicate that these optical systems may be considered as promising materials for Er-doped optical amplifiers operating within third telecommunication window.     

Thermal properties across threshold compositions in Ge-As-Se glasses

The Ge-As-Se chalcogenide glasses is an interesting system to test the validity of different constraint models proposed for these materials, in view of the fact that this system has a wide glass forming range which makes it possible to measure composition dependent properties over ranges covering most predicted thresholds. We have measured the thermal parameters—thermal diffusivity, thermal effusivity, thermal conductivity and heat capacity—of Ge-As-Se glasses covering composition range in which thresholds in physical properties have been predicted for covalent glasses employing a modified photopyroelectric technique. Our results show that this system exhibits a minimum in heat capacity at an average coordination number Z = 2.4 corresponding to a 3-D network as per the Phillips-Thorpe model, whereas thermal conductivity exhibits a threshold maximum at Z = 2.67 which is in agreement with the Tanaka model.     

Thermal properties and surface reactivity in simulated body fluid of new strontium ion-containing phosphate glasses

In this paper, we investigate the effect of SrO substitution for CaO in 50P₂O₅–10Na₂–(40?x)CaO–xSrO glass system (x from 0 to 40) on the thermal and structural properties and also on the glass reactivity in simulated body fluid (SBF) in order to find new glass candidates for biomedical glass fibers. The addition of SrO at the expense of CaO seems to restrain the leaching of phosphate ions in the solution limiting the reduction of the solution pH. We observed the formation of an apatite layer at the surface of the glasses when in contact with SBF. SrO and MgO were found in the apatite layer of the strontium ion-containing glasses, the concentration of which increases with an increase of SrO content. We think that it is the presence of MgO and SrO in the layer which limits the leaching of phosphate in the solution and thus the glass dissolution in SBF.     

Thermal and optical properties of tellurite glasses doped erbium

Er³⁺-doped tellurite glasses with molar compositions of 75TeO₂–20ZnO–(5 − x) Na₂O–xEr₂O₃ (x = 0, 0.5, 1, 2, 3, and 4 mol%) have been elaborated from the melt-quenching method. The effects of Er₂O₃ concentration on the thermal stability and optical properties of tellurite glasses have been discussed. From the differential scanning calorimetry (DSC) profile, the glass transition temperature T _g, and crystallization onset temperature T _x are estimated. The thermal stability factor, defined as ∆T = T _x − T _g, was higher than 100 °C. It suggests that tellurite glass exhibits a good thermal stability and consequently is suitable to be a potential candidate for fiber drawing. Furthermore, the stability factor increases with Er₂O₃ concentration up to 2 mol% then presents a continue decrease suggesting of beginning of crystallization of highly doped tellurite glasses. The refractive index and extinction coefficient data were obtained by analyzing the experimental spectra of tanΨ and cos∆ measured by spectroscopic ellipsometry (SE). The complex dielectric functions (ε = ε₁ + iε₂) of the samples were estimated from regression analysis. The fundamental absorption edge has been identified from the optical absorption spectra and was analyzed in terms of the theory proposed by Davis and Mott. The values of optical band gap for direct and indirect allowed transitions have been determined. An important decrease of the optical band gap was found after Er doping. It was assigned to structural changes induced from the formation of non-bridging oxygen. The absorption coefficient just below the absorption edge varies exponentially with photon energy indicating the presence of Urbach’s tail. The origin of the Urbach energy is associated with the phonon-assisted indirect transitions.     

Rare-earth containing nanocrystal precipitation and up-conversion luminescence in oxyfluoride glasses

Rare-earth ion doped oxyfluoride glass with a composition of 25SiO2 x 5GeO2 x 15AIO1.5 x 40PbF2 x 10PbO x (4.9 - x)GdF3 x 0.1HoF3 x xYbF3 (x = 0, 0.1,0.2, 0.5,1,2, 3, and 4) in molar ratio was developed. When the oxyfluoride glasses are heat-treated at the first crystallization temperature, the glasses give transparent glass-ceramics in which rare-earth-containing fluorite-type nanocrystals of about 17.2 nm in diameter uniformly precipitated in the glass matrix. Comparing with the glasses before heat treatment, the glass ceramics exhibit very strong up-conversion luminescence under 980-nm light excitation. Rare-earth-containing nanocrystals were also space selectively precipitated upon laser irradiation in an oxyfluoride glass; the size of precipitated nanocrystals can be controlled by laser power and scan speed. The intensity of the green up-conversion luminescence is strongly dependent on the precipitation of beta-PbF2 nanocrystals and the YbF3 concentration. The reasons for the highly efficient Ho3+ up-conversion luminescence are discussed.     

Oxyfluorotellurite glasses doped by dysprosium ions. Thermal and optical properties

The paper shows results of investigation of thermal and optical properties of oxyfluorotellurite (65 − x)TeO₂–20ZnF₂–12Pb₂O₅–3Nb₂O₅–xDy₂O₃ (x = 0.5, 2 and 5) glass systems. Thermal stability and the onset of crystallization of the materials were monitored by differential thermal analysis (DTA). It was found that characteristic parameters, namely glass transition temperatures (T_g), onset of crystallization temperatures (T_c) and thermal stability criteria ΔT and H’ increased with increasing Dy₂O₃ content indicating that the incorporation of dysprosium ions improves substantially thermal stability of glass system under study.Optical absorption and emission spectra of Dy³⁺ ions in oxyfluorotellurite glass were investigated at room temperature in the visible (VIS) and near-infrared (NIR) region. Oscillator strengths, phenomenological Judd–Ofelt (JO) intensity parameters Ω_2,4,6, radiative transition probabilities, branching ratios and radiative lifetimes of luminescent levels were determined. Decay curves of the ⁴F_9/2 luminescence of incorporated Dy³⁺ ions were recorded and analysed. Lifetimes and the luminescence dynamics were studied as a function of the Dy₂O₃ concentration. It was concluded that good thermal stability combined with desirable spectroscopic parameters of investigated dysprosium-doped oxyfluorotellurite glass point at the suitability of this material for the design of UV-excited visible phosphors.     

Effects of GeO2 on the thermal stability and optical properties of Er/Yb-codoped oxyfluoride tellurite glasses

The aim of this article was to study the influence of GeO₂ on the thermal stability and optical properties of Er³⁺/Yb³⁺ codoped (70 − x)TeO₂–xGeO₂–PbF₂–BaF₂ (TGEYx) glasses prepared by using a melting method. The properties of Er³⁺/Yb³⁺ codoped glasses were investigated by using differential scanning calorimetry, upconversion luminescence, Raman and optical absorption spectra. The results indicated that TGEY35 glass with the germanate–tellurite mixed network showed the best thermal stability and poor crystallization tendency. With increasing the GeO₂ content, the maximum phonon energy of oxyfluoride tellurite glass network increased, while the phonon density decreased. The upconversion emission intensities enhanced obviously based on the decreasing phonon density of glass hosts, while the increasing red emission (657 nm) with the increase of GeO₂ concentration was attributed to the relative larger maximum phonon energy which matching the energy gap between the pertinent ⁴S_3/2 and ⁴F_9/2 levels.     

Thermal expansion of lead silicate glasses

The thermal expansion, when heated from 77 to 273 K, of two samples of lead silicate glass, containing 21 and 28.5 mol % PbO, has been measured. The temperature dependence of the thermal expansion coefficient,α, is in qualitative agreement with the expansion behaviour of sodium silicate glass. However, the addition of ∼ 21 mol % PbO to silica is required to produce an increase in the magnitude ofα comparable to the addition of only ∼ 10 mol % Na₂O. The differences in the magnitudes ofα for lead and soda glasses are considered in the right of previous proposals for their structures.