Electrooptical Kerr phenomenon and Raman spectroscopy of one lithium–niobium–silicate glass-forming system

Raman spectra and electrooptical Kerr coefficients of glasses belonging to one lithium–niobate–silicate glass-forming system xNb₂O₅ · (66 ? x)SiO₂ · 19Li₂O · 11K₂O · 2B₂O₃ · 2CdO are studied. It has been found that these glasses demonstrate a record value of electrooptical Kerr coefficient; the glass with x = 35 showed electrooptical Kerr coefficient equal to 266 × 10^?16 m/V². Using Raman spectroscopy combined with the concept of Constant Stoichiometric Groupings, a correlation of electrooptical Kerr coefficients of these glasses with the content of Li₂O · Nb₂O₅ (or 2LiNbO₃) groupings has been demonstrated. The hypothesis that electrooptical Kerr sensitivity of glasses is related to the ordered regions with composition and symmetry corresponding to some of known electrooptical crystals has been verified. These regions, which the authors called ‘Crystal Motifs’, are identified with the groupings found in studying Raman spectra of the glasses.     

Effect of OH− content on emission properties in Er3+-doped tellurite glasses

A series of tellurite glasses of composition, 75TeO₂–20ZnO–(5 ? x)La₂O₃–xEr₂O₃ (x = 0.05, 0.1, 0.3, 0.6, 1.0, 2.0, and 3.0 mol%) with different hydroxl content were prepared. The effect of Er³⁺ and OH^? groups concentration on the emission properties of Er³⁺: ⁴I_13/2 → ⁴I_15/2 transition in tellurite glasses was investigated. The constant K_OH–Er for Er³⁺ in tellurite glasses, which represents the strength of interaction between Er³⁺ and OH^? groups in the case of energy migration, was about 14 × 10^?19 cm⁴ s^?1. The interaction parameter C_Er,Er for the migration rate of Er³⁺: ⁴I_13/2 → ⁴I_13/2 transition in tellurite glass was 46 × 10^?40 cm², which indicates that concentration quenching in Er³⁺-doped modified tellurite glass for a given Er³⁺ concentration is much stronger than in silicate and phosphate glasses.     

Thermal and optical properties of TeO2–ZnO–BaO glasses

We report the results of a systematic study of the thermal and optical properties of a new family of tellurite glasses, TeO₂–ZnO–BaO (TZBa), as a function of the barium oxide mole fraction and compare them with those of TeO₂–ZnO–Na₂O (TZN). The characteristic temperatures of this new glass family (glass transition, T_g, crystallization, T_x, and melting, T_m) increase significantly with BaO content and the glasses are more thermally stable (greater ΔT = T_x ? T_g) than TZN glasses. Relative to these, Raman gain coefficient of the TZBa glasses also increases by approximately 40% as well as the Raman shift from ~ 680 cm^? 1 to ~ 770 cm^? 1. The latter shift is due to the modification of the glass with the creation of non-bridging oxygen ions in the glass network. Raman spectroscopy allows us to monitor the changes in the glass network resulting from the introduction of BaO.     

The preparation and structural studies in the (80 − x)TeO2–20ZnO–(x)Er2O3 glass system

Er³⁺-doped tellurite glasses of the (80 ? x)TeO₂–20ZnO–(x)Er₂O₃ system (0.5 mol% ? x ? 2.5 mol%) have successfully been made by melt-quenching technique and their structure has been investigated by means of DTA and Raman spectroscopy. The DTA results show the thermal parameters; such as the glass transition temperature (T_g) and crystallization temperature (T_c) were determined. It is found that this system provides a stable and wide glass formation range in which the glass stability around 99–140 °C may be obtained. The Raman spectroscopy used the structural studies in the glass system. Two Raman shift peaks were observed around 640–670 cm^?1 and 720–740 cm^?1, which correspond to the stretching vibration mode of TeO₄ tbp and TeO₃ tp, respectively. It is found that the spectral shift in Raman spectra is depending on the Er₂O₃ content. This evolution is an indication of the changes in the basic unit of the glass structure.     

Characterization of B2O3 and/or WO3 containing tellurite glasses

Characterization of B₂O₃ and/or WO₃ containing tellurite glasses was realized in the 0.80TeO₂–(0.20 ? x)WO₃ ? xB₂O₃ system (0 ≤ x ≤ 0.20 in molar ratio) by using differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectrometry techniques. Glasses were prepared with a conventional melt-quenching technique at 750 °C. To recognize the thermal behavior of the glasses, glass transition and crystallization temperatures, glass stability value, glass transition activation energy, fragility parameter were calculated from the thermal analyses. Density, molar volume, oxygen molar volume and oxygen packing density values were determined to investigate the physical properties of glasses. Fourier transform infrared spectra were interpreted in terms of the structural transformations on the glass network, according to the changing B₂O₃ and/or WO₃ content. Crystallization behavior of the glasses was investigated by in situ X-ray diffraction measurements and microstructural characterization was realized by scanning electron microscopy and energy dispersive X-ray spectrometry analyses.     

Optical band gap and Raman spectra in some (Bi2O3)x(WO3)y(TeO2)100−x−y and (PbO)x(WO3)y(TeO2)100−x−y glasses

The glasses representing (Bi₂O₃)_x(WO₃)_y(TeO₂)_100?x?y and (PbO)_x(WO₃)_y(TeO₂)_100?x?y systems were prepared. The dilatometric glass-transition temperatures of examined glass samples were found in the region 383–434 °C, the coefficient of thermal expansion varied from 12 to 16 ppm/°C and the density ranged from 6.30₂ to 6.80₈ g/cm³. From the optical transmission measurements of thin glassy bulk samples prepared by a glass blowing, the optical gap values were found in the narrow region 3.21–3.36 eV. For the temperature interval 300–480 K, the values of the temperature coefficient of the optical band gap varied from 3.7 × 10^?4 to 5.24 × 10^?4 eV/K. It is suggested that Raman feature observed at around 350 cm^?1 can be assigned to an overlap of Raman bands attributed to WO₆ corner shared octahedra and to the following three atomic linkages: Bi–O–Te, Pb–O–Te and W–O–Te.     

Mixed transition-ion effect in the glass system: Fe2O3-MnO-TeO2

In earlier studies on phosphate and tellurite glasses containing vanadium and iron oxides, non-linear variation of physical properties as functions of the ratios of the transition ions (V/V + Fe) were observed. The most striking effect was observed with electrical conductivity, where a 3 orders of magnitude reduction in conductivity was observed at a V/V + Fe ratio of ~ 0.4. The effect was termed Mixed Transition-ion Effect or MTE. In phosphate glasses, however, MTE was not observed when one of the transition ions was manganese. It was concluded that Mn does not contribute to conduction in these glasses. In the present study, we demonstrate a mixed transition ion effect in tellurite glasses containing MnO and Fe₂O₃ (xFe₂O₃(0.2 ? x) MnO0.8TeO₂ with x varying from 0 to 0.2). A maximum in the property at an intermediate composition (x = 8.5 mol%), was observed in DC resistivity, activation energy, molar volume etc. Mossbauer and optical absorption (UV–VIS–NIR) measurements were performed on these glasses and the transport mechanism has been identified to be hopping of small polarons between Fe^3 + (Mn^3 +) and Fe^2 + (Mn^2 +) sites.     

Structural and magnetic investigations of Fe2O3–TeO2 glasses

A series of tellurite glasses containing Fe₂O₃ with the nominal composition x(Fe₂O₃)–(1−x)(TeO₂), where x = 0.05, 0.10, 0.15, and 0.20, have been synthesized and investigated using X-ray photoelectron spectroscopy (XPS) and magnetization techniques. The Te 3d core level spectra for all glass samples show symmetrical peaks at essentially the same binding energies as measured for TeO₂ indicating that the chemical environment of the Te atoms in these glasses does not vary significantly with the addition of Fe₂O₃. Furthermore, the full-width at half-maximum (FWHM) of each peak does not vary with increasing Fe₂O₃ content which suggests that the Te ions exist in a single configuration, namely TeO₄ trigonal bipyramid (tbp). The O 1s spectra are narrow and symmetric for all compositions such that oxygen atoms in the Te–O–Te, Fe–O–Fe and Te–O–Fe configurations must have similar binding energies. The analysis of the Fe 3p spectra indicates the presence of Fe³⁺ ions only, which is consistent with the valence state of the Fe ions determined from magnetic susceptibility measurements.     

Efficient 1.53 μm erbium light emission in heavily Er-doped titania-modified aluminium tellurite glasses

Ti–Al co-doped erbium tellurite glasses have been obtained by melting mixed Er₂O₃, TiO₂ and TeO₂ batches in Al₂O₃ crucibles. By crucible dissolution Al₂O₃ amounts from 11.5 to 18.6 mol% were introduced in the synthesized glasses. Differential thermal analysis of glasses points to a strong dependence of glass transition temperature T_g with the substitution extent of TeO₂ by the doping oxides. No crystallization features are observed up to 450 °C. The spectral features and decay kinetics of the infrared photoluminescence of erbium demonstrate the possibility to achieve more than 50% of quantum yield of light-emission at Er³⁺ concentrations as large as 10²¹ cm⁻³, with about 2 ms of lifetime, 8 × 10⁻²¹ cm² of stimulated emission cross section, and no saturation at pump power densities higher than 10 kW cm⁻². The study of the kinetics of Er–Er energy transfer suggests to ascribe these features to a particularly homogeneous dispersion of Er³⁺ ions in the modified tellurite network. Raman scattering measurements of the spectral distribution of vibrational modes evidence that the introduction of doping oxides leads to an increase of structural disorder without crystallization effects.     

Effects of Fe2O3 replacement of ZnO on elastic and structural properties of 80TeO2–(20 − x)ZnO–xFe2O3 tellurite glass system

Ternary tellurite glasses with the chemical formula 80TeO₂–(2 ? x)ZnO–xFe₂O₃ (x = 0–15 mol%) have been prepared by the melt-quenching method. Elastic and structural properties of the glasses were investigated by measuring both longitudinal and shear velocities using the pulse-echo overlap method at 5 MHz and Fourier transform infrared (FTIR) spectroscopy, respectively. Both longitudinal and shear velocity showed a large increase of 3.40% and 4.68%, respectively, at x = 5 mol% before a smaller increase for x > 5 mol%. Interestingly, longitudinal modulus (L), shear modulus (G), bulk modulus (K) and Young's modulus (E) recorded similar trends with increase in Fe₂O₃. The initial large increases in shear and longitudinal velocity and related elastic moduli observed at x = 5 mol% are suggested to be due to structural modification which enhances rigidity of the glass network. FTIR analysis showed increase in bridging oxygen (BO) as indicated by the relative intensity of the TeO₄ assigned peaks and increase in intensity of the FeO₆ assigned peak (~ 451 cm^? 1) which indicates that Fe acts as a modifier in the glass network. The increase in rigidity of the glass system is suggested to be due to the increase of BO together with the formation of strong covalent FeO bond. Quantitative analysis based on the bulk compression and ring deformation models showed that the k_bc/k_exp value decreased gradually from 2.41 (x = 0 mol%) to 2.02 (x = 15 mol%) which infers that the glass system became a relatively more open 3D network as Fe₂O₃ was increased.     

Thermo-optical properties and nonradiative quantum efficiency of Er3+-doped and Er3+/Tm3+-co-doped tellurite glasses

Thermal lens (TL) measurements were performed in tellurite glasses, 70TeO₂–19WO₃–7Na₂O–4Nb₂O₅ (mol%), undoped, doped with Er³⁺ (1.19 × 10²⁰ ions/cm³) and co-doped with Er³⁺ (1.19 × 10²⁰ ions/cm³)/Tm³⁺ (1.56 × 10²⁰ ions/cm³). The absolute nonradiative quantum efficiency (ϕ) was determined by the TL method. The ϕ values for Er³⁺/Tm³⁺-co-doped and Er³⁺-doped tellurite glasses were 0.98 and 0.74, respectively. Fluorescence spectra were performed at λ_e = 488 nm and used to estimate the fluorescence quantum efficiency (η) using the TL results. These values were compared with results obtained by Judd–Ofelt calculations.     

Production and properties of high purity TeO2− WO3−(La2O3, Bi2O3) and TeO2− ZnO−Na2O−Bi2O3 glasses

TeO₂–WO₃ (TW), TeO₂–WO₃–La₂O₃ (TWL), TeO₂–WO₃–La₂O₃–Bi₂O₃ (TWLB) and TeO₂–ZnO–Na₂O–Bi₂O₃ (TZNB) glasses were produced by high-purity oxide mixtures melting in platinum or gold crucible at 800 °C in the atmosphere of purified oxygen. The total content of Cu, Mn, Fe, Co and Ni impurities was not more than 0.1–0.5 ppm wt in the initial oxides and glasses. The stability of TZNB glasses to crystallization, characterized by (T_x ? T_g) value more than 150 °C, was demonstrated by DSC measurements at heating rate 10 K/min. In the case of La₂O₃-containing glasses the thermal effects of both crystallization and fusion of the crystallized phases were not observed. The hydroxyl groups absorption coefficients of pure tellurite glasses at the maximum of the absorption band (λ ~ 3 μm) were in the region of 0.012–0.001 cm^?1. The optical absorption losses, measured by the laser calorimetry method at λ = 1.56 and 1.97 μm, did not exceed 100 dB/km.     

Majority charge carrier reversal and its effect on thermal and electron transport in xV2O5–(1 − x) As2O3 glasses

DC resistivity, thermopower and optical absorption of xV₂O₅–(1 ? x) As₂O₃ (0.58 ≤ x ≤ 0.93) glasses have been studied as a function of composition. The transport mechanism in these glasses has been identified to be a combination of hopping of small polarons between V⁴⁺ and V⁵⁺ sites and small bipolarons between As³⁺ and As⁵⁺ sites respectively. Electrical conductivity is found to be more of a function of vanadium content than arsenic concentration in the glasses, indicating that the contribution of bipolarons to the conductivity is negligible. Thermopower has also been found to be sensitive to the composition of the glasses. At low vanadium concentrations, the thermopower is negative, which exhibits a sign reversal as vanadium concentration is increased (at x = 0.7). An important feature of these glasses is that the thermopower is not a function of [V⁵⁺]/[V⁴⁺] ratio, as is normally observed in vanadate glasses, and such a phenomenon suggests that the arsenic ions (bipolarons) in these glasses contribute to the thermal transport phenomena in a significant way.     

Structure and properties of the 70Li2S · (30 − x)P2S5 · xP2O5 oxysulfide glasses and glass–ceramics

The 70Li₂S · (30 ? x)P₂S₅ · xP₂O₅ (mol%) oxysulfide glasses were prepared by the melt quenching method. The glasses were prepared in the composition range 0 ≦ x ≦ 10. The glass–ceramics were prepared by heating the glasses over crystallization temperatures. The PO_nS_3?n (n = 1–3) oxysulfide units were produced in the glasses and glass–ceramics by partial substituting P₂O₅ for P₂S₅. In particular, the P₂OS₆^4? unit would be produced by substituting a small amount of P₂O₅ for P₂S₅. The oxygen atoms were incorporated into the Li₇P₃S₁₁ crystal structure because the diffraction peaks of the oxysulfide glass–ceramic shifted to the higher angle side. The glass–ceramic with 3 mol% of P₂O₅ exhibited the highest conductivity of 3.0 × 10^?3 S cm^?1 and the lowest activation energy for conduction of 16 kJ mol^?1. The P₂OS₆^4? dimer units in the oxygen-incorporated Li₇P₃S₁₁ crystal would improve conductive behavior of the Li₂S–P₂S₅ glass–ceramics.     

Fast ion conducting phosphate glasses and glass ceramic composites: Promising materials for solid state batteries

Fast ion conducting (FIC) phosphate glasses and glass ceramic composites have gained considerable importance due to their potential applications in the fabrication of solid-state batteries and other electrochemical devices. We, therefore, present an overview on various types of FIC glasses and glass ceramic composites. Silver phosphate glasses doped with different weight percent of lithium chloride (1, 5, 10 and 15 wt.%) were synthesized by melt quenching technique. The Ag₂O–P₂O₅–(15 wt.%) LiCl glass exhibited the maximum electrical conductivity (σ = 8.91 × 10^? 5 S cm^? 1 at room temperature and 4.16 × 10^? 3 S cm^? 1 at 200 °C). Using this glass as an amorphous host material, glass–ceramic composites of Ag₂O–P₂O₅–(15 wt.%) LiCl:xAl₂O₃ (x = 5–50 wt.%) were prepared. The ionic transference number, electrical conductivity, ionic mobility and carrier ion concentration of the synthesized samples were measured. Ag₂O–P₂O₅–(15 wt.%) LiCl:(25 wt.%) Al₂O₃ composite system exhibited the maximum σ value (σ = 3.32 × 10^? 4 S cm^? 1 at room temperature and 2.88 × 10^? 2 S cm^? 1 at 200 °C ). Solid‐state batteries using undoped Ag₂O–P₂O₅ glass, Ag₂O–P₂O₅–(15 wt.%) LiCl glass and glass ceramic composite containing 25 wt.% Al₂O₃ as electrolytes were fabricated. The open circuit voltage (OCV) values and discharge time of these cells were measured and compared. It is found that the glass ceramic composites show enhanced ionic conduction, better OCV value and discharge characteristics.     

Structure and properties of MoO3-containing zinc borophosphate glasses

ZnO–B₂O₃–P₂O₅ glasses doped with MoO₃ were investigated in the series (100?x)[0.5ZnO–0.1B₂O₃–0.4P₂O₅]–xMoO₃, where bulk glasses were obtained by slow cooling in air within the compositional region of 0 ? x ? 60 mol% MoO₃. The incorporation of MoO₃ into the parent zinc borophosphate glass results in a weakening of bond strength in the structural network, which induces a decrease in chemical durability and glass transition temperature. Raman spectra reflect the incorporation of molybdate groups into the glass network of the studied glasses by the presence of the polarized vibrational band at ≈976 cm^?1 ascribed to the MO_x symmetric stretching vibrations and the depolarized band at ≈878 cm^?1 ascribed to the Mo–O–Mo stretching vibration. The incorporation of molybdate units into the glass network results in the depolymerization of phosphate chains and the formation of P–O–Mo bonds, as reflected in Raman and ³¹P NMR spectra. According to the ¹¹B MAS NMR spectra, tetrahedral B(OP)_4?x(OMo)_x units are formed in the glasses, whereas only a small amount of BO₄ units is converted to BO₃ units in the MoO₃-rich glasses.     

Bond character,optical properties and ionic conductivity of Li2O/B2O3/SiO2/Al2O3 glass: Effect of structural substitution of Li2O for LiCl

A glass of composition (20 ? x)Li₂O–xLiCl–65B₂O₃–10SiO₂–5Al₂O₃ where 0 ? x ? 12.5 wt% is prepared using the normal melt-quenching technique. The optical constants and electrical conductivity and their correlation are investigated, furnished and discussed with the substitution of Li₂O for LiCl. The mechanism of the optical absorption and the calculated Urbach energy follow the rule of phonon-assisted transitions. The ionic conduction mechanism is determined by activation energy process. Substitution up to 10 wt% LiCl provides high ionic conductivity (1.9 × 10^?2 Ω^?1 m^?1) due to the high average electronegativity of LiCl which increases the polarizability of lithium ions. The small cation–anion distance approach confirmed the enhancement in ionic conductivity of LiCl containing glass compared to that of Li₂O. Due to the large size of Cl^? ions, there is an expansion of the lattice which in turn broadens the available path windows. For 12.5 wt% LiCl, anomalous density behavior is observed and a reduction in conductivity is occurred, σ = 5.4 × 10^?3 Ω^?1 m^?1. Owing to the model of bond fluctuation, the reduction is attributed to the increase in the alkali halide concentration which creates bottlenecks that hinder the motion of Li⁺ ions. The ionic conductivity character is strongly supported by the behavior of the glass ionicity factor, density, molar volume, refractive index, average boron–boron separation, molar refraction, metallization criterion and non-bridging oxygen concentration of the studied glass.     

The role of modifier’s cation valence in structural properties of TeO2-based glasses

The compositional invariance of the Raman spectra of (1 ? x)TeO₂–xM_nO_m glasses (M = Ti, Nb) is analyzed and interpreted as evidence for the conservatism of a framework-type constitution inherent to such glasses. This is assigned to the chemical similarity of cations in the X–O–Y bridges (X, Y = Te⁴⁺, Ti⁴⁺, Nb⁵⁺) considered as the framework building blocks. It is concluded that the atoms of metals having valence IV and V can be placed into the category of such cations, to which certain of the atoms with valence III can be added.     

Band gap determination by absorption spectrum fitting method (ASF) and structural properties of different compositions of (60−x) V2O5–40TeO2–xSb2O3 glasses

Glasses with compositions (60?x) V₂O₅–40TeO₂–xSb₂O₃ with 0 ? x ? 10 (in mol%) have been prepared using usual melt quenching method. The position of the absorption edge and hence the values of the optical band gap was found to depend on the glass composition. Using the Tauc model, the absorption spectrum fitting method (ASF) was employed to obtain the optical band gap. This method requires only the measurement of the absorbance spectrum of the sample. For each sample, the width of the band tail was determined. Also, the density and glass transition temperature values indicate that the rigidity and packing of the samples increase with increase in Sb₂O₃ concentration.     

Spectroscopic properties of Tm3+ doped TeO2-R2O-La2O3 glasses for 1.47 μm optical amplifiers

Upon excitation at 808 nm laser diode, an intense 1.47 μm infrared fluorescence has been observed with a broad full width at half maximum (FWHM) of about 124 nm for the Tm³⁺-doped TeO₂-K₂O-La₂O₃ glass. The Judd–Ofelt parameters found for this glass are: Ω₂ = 5.26 × 10^?20 cm², Ω₄ = 1.57 × 10^?20 cm² and Ω₆ = 1.44 × 10^?20 cm². The calculated emission cross-sections of the 1.47 μm transition are 3.57 × 10^?21 cm², respectively. It is noted that the gain bandwidth, σ_e × FWHM, of the glass is about 440 × 10^?28 cm³, which is significantly higher than that in ZBLAN and Gallate glasses, a high gain of 35.5 dB at 1470 nm can be obtained in a TKL glass fiber. TeO₂-R₂O (R = Li, Na, K)-La₂O₃ glasses has been considered to be more useful as a host for broadband optical fiber amplifier.