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.     

Properties and structure of (50 − x)BaO–xZnO–50P2O5 glasses

The thermal, mechanical, chemical properties and the structure of (50 − x)BaO–xZnO–50P₂O₅ (0 ⩽ x ⩽ 50 mol%) glasses were investigated. For these glasses, the density (ρ), glass transition temperature (T_g), dissolution rate (DR), ³¹P magic angle spinning nuclear magnetic resonance (MAS-NMR) spectra and Fourier-transformed infrared (FTIR) spectra were determined. As BaO was replaced by ZnO, all the properties were similarly decreased in density, Young’s modulus, T_g and water resistance. FTIR analyses revealed a shortening of phosphate chains by the shift of (P–O–P)_as band to a higher wave number owing to the substitution ZnO of BaO. The NMR spectra showed that the replacement of BaO by ZnO decreased the concentration of Q²-tetrahedral sites and increased that of Q¹-tetrahedral sites.     

Influence of various alkali and divalent metal oxides on phase transformations in NiO-doped glasses of the Li2O–Al2O3–SiO2–TiO2 system

Regularities of phase transformations in glasses of the Li₂O–Al₂O₃–SiO₂–TiO₂ system doped with up to 2.5 mol% of alkali- and divalent metal oxides were studied by X-ray diffraction analysis, Raman scattering and optical spectroscopy. Ni(II) ions were used as spectral probes of phase transformations because Ni(II)-ions enter the inhomogeneous regions formed during the phase separation and crystallization, and their absorption spectra change with heat-treatment temperature reflecting formation of aluminotitanate amorphous regions, spinel nanosized crystals and β-quartz solid solutions, consequently.It was demonstrated that the technological additives do not change the sequence of the phases' formation but accelerate the liquid phase separation and crystallization. Addition of MgO and ZnO leads to increasing the temperature range of spinel precipitation. Addition of CaO, BaO and PbO results in increasing the light scattering of prepared glass-ceramics.In selection of the technological additives for decreasing the melting temperature of glass-ceramics for optical and photonic applications the influence of the additives on the structure and optical properties of the prepared material should be considered.     

Development of novel ternary tellurite glasses for high temperature fiber optic mid-IR chemical sensing

The properties of novel ternary tellurite glasses, based on the TeO₂–BaO–Bi₂O₃ system, are reported for their applications in on-line chemical sensing and process control by characterizing the fundamental frequencies of molecular vibrations in the 2–5 μm spectral region of mid-IR. The chemical sensing for process control also requires above room temperature operation (>100 °C) for prolonged periods of time. Bulk samples of ternary tellurite glasses with a number of different compositions were prepared using heavy molecular weight oxides of TeO₂, BaO, and Bi₂O₃. Infrared and Raman spectroscopic analysis was carried out together with differential thermal analysis to study the relationship between glass structure and thermal and viscosity properties. The temperature dependence of the viscosities of the glasses is also reported. The compositional dependence of Raman frequency shifts and the corresponding change in the coordination of Te–O structure is discussed. The results from the IR edge, reflection spectroscopic, and wavelength dependence of refractive index are also reported.     

Thermal properties of barium titanium borate glasses measured by thermal lens technique

In this paper, thermal lens spectrometry was used to determine the thermal properties of barium titanium borate glasses as a function of the amount of TiO₂ in the ratios 8/9 and 1/1 of BaO–B₂O₃. The thermal lens technique was shown to be sensitive to the variation of TiO₂ and the ratio of BaO/B₂O₃, through thermal diffusivity and conductivity, with different behavior for the ratios 1/1 and 8/9. An increase in thermal diffusivity and conductivity as a function of TiO₂ was observed, and this behavior was ascribed to the fact that titanium acts as a glassy-former, being more active in the ratio 8/9.     

Preparation and characterization of CuO doped Bi2O3–B2O3–BaO–ZnO glass system for transparent dielectric layer

The electrical, thermal, optical, and morphological properties of CUO doped Bi₂O₃–B₂O₃–BaO–ZnO glasses were studied as a PbO-free, low firing transparent dielectric layer for plasma display panels (PDP). CuO improved the transmittance of Bi₂O₃–B₂O₃–BaO–ZnO by up to 84% in the visible region, eliminating a yellowish color typical of Bi₂O₃–B₂O₃–BaO–ZnO. A slight absorption within the near infrared (NIR) region was also observed. The glass transition temperature (T_g), thermal coefficient of expansion (TCE), and root-mean square (rms) roughness of 0.005 wt% CuO doped Bi₂O₃–B₂O₃–BaO–ZnO were found to be 455 °C, 81.4 × 10⁻⁷/K, respectively, and 162 ± 14 Å, which satisfied the requirements for a transparent dielectric layer for PDP application.     

On the origin of the high Kerr coefficient measured in thallium–zinc–tellurite glasses

Measurements of Kerr electrooptical sensitivity of several zinc–thallium–tellurite glasses are presented, and composition dependence of Kerr sensitivity is compared with the dependence of the second harmonic generation efficiency collected for optically poled TeO₂–TlO_0.5–ZnO glasses. These data being analyzed jointly with Raman measurements data allowed us to conclude that the high electrooptical Kerr coefficient and nonlinearity of Tl₂O–ZnO–TeO₂ glasses, and their sharp increase with augmenting concentration of thallium oxide TlO_0.5 above 15% should be attributed to the presence of Tl⁺ cations having very high non-linear polarizability most likely related to their electronic lone pairs.     

Structure and properties of NaPO3–ZnO–Nb2O5–Al2O3 glasses

In an effort to design low-melting, durable, transparent glasses, two series of glasses have been prepared in the NaPO₃–ZnO–Nb₂O₅–Al₂O₃ system with ZnO/Nb₂O₅ ratio of 2 and 1. The addition of ZnO and Nb₂O₅ to the sodium aluminophosphate matrix yields a linear increase of properties such as glass transition temperature, density, refractive index and elastic moduli. The chemical durability is also significantly, but nonlinearly, improved. The glass with the highest niobium concentration, 55NaPO₃–20ZnO–20Nb₂O₅–5Al₂O₃ was found to have a dissolution rate of 4.5 × 10^? 8 g cm^? 2 min^? 1, comparable to window glass. Structural models of the glasses were developed using Raman spectroscopy and nuclear magnetic resonance spectroscopy, and the models were correlated with the compositional dependence of the properties.     

Vibrational spectra and structure of chloro-fluorozirconate glasses

A series of barium chloro-fluorozirconate glasses have been prepared. Their IR absorption, IR reflectivity and Raman spectra have been measured down to 33 cm^?1. The glass transition and crystallization temperatures have also been measured. The high frequency IR absorption and Raman modes of the chloro-fluorozirconate glasses have been assigned as in fluorozirconate glasses. The IR reflection spectra of chloride-containing glasses differed from the fluorozirconates in that one band was clearly related to Cl atom motions. The structure of the glasses probably consists of zig-zag chains of ZrCl₂F₄ mixed halide octahedra plus a pure fluoride matrix whose structure is similar to that of a ZrF₄BaF₂ glass with the same composition.     

Glasses in the system of MnNbOF5–BaF2–BiF3–ErF3

The glasses in the MnNbOF₅–BaF₂–5BiF₃–ErF₃ system were obtained and their thermal and optical properties were studied. The specialties of crystallization depending on system composition are showed. The glass structure is discussed based on results of the IR and Raman spectra study. During the studies of inelastic light scattering, there revealed a strong photoluminescence, produced by erbium emission, whose intensity depends not only on the erbium trifluoride content in glass, but also on the glass network structure.     

Quantitation of sulfate solubility in borosilicate glasses using Raman spectroscopy

Raman spectroscopy is used here as an innovative technique to investigate sulfate content in borosilicate glasses. Using Raman spectroscopy after having heated the material, the evolution of sulfate amounts can be followed as a function of temperature, time and chemical composition of the starting matrix. The accuracy of this technique was verified using electron probe micro analysis (EPMA), on two systems of glasses (SiO₂–B₂O₃–Na₂O (SBNa) and SiO₂–B₂O₃–BaO (SBBa)) in order to compare the effect of alkaline or alkaline-earth elements on sulfur speciation and incorporation. To quantitate sulfate content with Raman spectroscopy, the integrated intensity of the sulfate band at 990 cm^?1 was scaled to the sum of the integrated bands between 850 and 1250 cm^?1, bands that are assigned to Qⁿ silica units. Calibration curves were then determined for different samples. The determination of sulfate contents with Raman spectroscopy analysis is possible with an accuracy of approximately 0.1 wt% depending on the composition of the glass. It mainly allows us to follow sulfate removal during the elaboration process and to establish kinetic curves of sulfate release as a function of the viscosity of the borosilicate glass.     

Use of a fluorine-containing solvent in the synthesis of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7 − δ</Subscript> single crystals

A laboratory technological procedure has been developed for the synthesis of high-temperature superconducting YBa₂Cu₃O_{7 ? δ} single crystals (T _c ～ 90 K, ΔT _c ～ 1.0 K) up to 0.25 cm² in size from a nonstoichiometric fluorine-containing flux of (YO_1.5)(BaO)_{4 ? x}(BaF₂)_x(CuO)₁₀, where 2 ≥ x ≥ 0, using a combination of enhanced nucleation and directional crystallization by the Czochralski method. Studies using differential thermal analysis demonstrated that the addition of BaF₂ decreased the eutectic-crystallization temperature and increased the crystal-growth rate. The optimum concentration of BaF₂ in the starting melt composition was found (x = 0.2). The single-crystal surface was studied by atomic-force nanoscopy. The morphology of single crystals that have been synthesized from a melt of their own components differs substantially from that of crystals grown from a BaF₂-containing melt.     

Effect of high-energy electron irradiation in an electron microscope column on fluorides of alkaline earth elements (CaF2, SrF2, and BaF2)

The effect of high-energy (150 eV) electron irradiation in an electron microscope column on crystals of fluorides of alkaline earth elements CaF₂, SrF₂, and BaF₂ is studied. During structural investigations by electron diffraction and electron microscopy, the electron irradiation causes chemical changes in MF₂ crystals such as the desorption of fluorine and the accumulation of oxygen in the irradiated area with the formation of oxide MO. The fluorine desorption rate increases significantly when the electron-beam density exceeds the threshold value of ∼2 × 10³ pA/cm²). In BaF₂ samples, the transformation of BaO into Ba(OH)₂ was observed when irradiation stopped. The renewal of irradiation is accompanied by the inverse transformation of Ba(OH)₂ into BaO. In the initial stage of irradiation of all MF₂ compounds, the oxide phase is in the single-crystal state with a lattice highly matched with the MF₂ matrix. When the irradiation dose is increased, the oxide phase passes to the polycrystalline phase. Gaseous products of MF₂ destruction (in the form of bubbles several nanometers in diameter) form a rectangular array with a period of ∼20 nm in the sample.     

Thermal and optical properties of TeO2–BaO–SrO–Nb2O5 based glasses: New broadband Raman gain media

We systematically added WO₃ (up to 10 mol%) and P₂O₅ (up to 16 mol%) in TeO₂–BaO–SrO–Nb₂O₅ (TBSN) glass system and studied thermal and optical properties of the resultant glasses. The dependences of the additive concentration on glass transition (T_g) and crystallization (T_x) temperatures are presented. The TBSN glass added with ⩾4 mol% WO₃ and P₂O₅ showed high stability against crystallization. The changes in optical band gap energy due to WO₃ and P₂O₅ addition was studied using UV–VIS–NIR absorption spectrometry. The WO₃ addition shifted the optical band gap to longer wavelengths, whereas P₂O₅ addition shifted that to shorter wavelengths. Effects of the WO₃ and P₂O₅ addition on the Raman spectra of TBSN glass are clarified. New Raman bands due to WO₄ and PO₄ tetrahedra formed in the resultant glasses broadened their Raman spectra. Present glasses are characterized by higher thermal stability and wider Raman spectra, therefore, they are promising candidates for fiber Raman amplifiers in photonics systems.     

The effect of RO (R = Mg,Ca, Ba and Zn) on physical properties of Na2O/Al2O3/B2O3/SiO2 glasses for the preparation of gradient index micro lenses

Glasses in the system Na₂O–Al₂O₃–B₂O₃–SiO₂ doped with MgO, CaO, BaO or ZnO (concentrations: 2.5%–5 mol%) were melted from the raw materials and studied with respect to their densities, hydrolytic durabilities, crystal growth velocities, specific ionic conductivities, refractive indices, Abbe numbers and optical transmissions. The samples were ion exchanged in a NaNO₃/AgNO₃ salt melt in order to determine the Na⁺/Ag⁺ interdiffusion coefficients and the refractive indices, Abbe numbers and optical transmissions of the ion exchanged silver containing glasses. Glasses doped with ZnO are advantageous for the production of gradient index lenses due to their improved chemical durability and smaller crystal growth velocities at viscosities in the range of 10⁵–10⁶ dPa s. The optical properties of these glasses are similar to those of glasses without RO.     

Dependence of fluorescence properties on substitution of BaF2 for BaO in barium gallo-germanate glass

3.5 mol%, 6.5 mol%, 9.5 mol%, and 12.5 mol% BaF₂ were gradually substituted for BaO in 0.3 mol% Tm₂O₃ doped 12.5 BaO-12.5 Ga₂O₃-75 GeO₂ (BGG) glasses to study the effect of the substitution on the OH⁻ elimination and emission properties. The FTIR spectral demonstrated that the substitution effectively eliminated OH⁻ groups and 9.5 mol% BaF₂ was enough for the OH⁻ elimination. The J-O parameters of all the samples were calculated according to J-O theory. The calculation showed that the Ω₂ parameter decreased monotonically with BaF₂ content increasing, while Ω₄ and Ω₆ did not change much. The radiative lifetime increased while BaF₂ content increased as well. The emission cross section of ³F₄ → ³H₆ transition was calculated by the F-L formula. However, it decreased with the gradual BaF₂ addition.

Research Highlights

? OH⁻ groups were eliminated by the substitution of BaF₂ for BaO in (BGG) glass. ? The optimal substitution level of BaF₂ was 9.5 mol% for OH⁻ elimination. ? The Ω₂ parameter decreased monotonically by the elimination. ? The emission cross section of ³F₄ → ³H₆ transition was decreased by the substitution.     

Stabilization of heavy metals fluoride glasses

A new class of fluoride glasses has been isolated in the ternary system containing one transition metal fluoride ZnF₂, one rare earth fluoride YbF₃ and one actinide fluoride ThF₄. The controlled addition of BaF₂ playing the role of modifier allows the stabilization of glasses with low rate of crystallization in the quaternary system BaF₂ThF₄ZnF₂YbF₃. The infrared transmission can be extended to the 7–8 μ region, a significant improvement over the fluorozirconate glasses.     

Crystallization kinetics of fluoride nanocrystals in oxyfluoride glasses

Oxyfluoride glasses containing different alkaline earth fluoride (CaF₂, SrF₂, and BaF₂) were prepared and their crystallization behavior was analyzed using non-isothermal kinetics based upon differential scanning calorimetry (DSC) scan results. The glass containing CaF₂ showed the fastest kinetics for CaF₂ crystallization, while that containing BaF₂ showed the slowest kinetics for BaF₂ crystallization. On the other hand, all the oxyfluoride glasses showed very similar behavior in the crystallization of glass matrices. The difference in the crystallization behavior of the oxyfluoride glasses was discussed based upon the difference in the size of alkaline earth ions and the difference in the dissociation energy of alkaline earth-fluorine bonds.     

Short-range structure and in vitro behavior of ZnO–CaO–P2O5 bioglasses

Ternary zinc–calcium-phosphate glasses prepared by classical melting method were characterized through X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) along with energy dispersive X-ray analysis (EDAX), Fourier Transform InfraRed (FTIR) and Raman spectroscopy. The study of these glasses was done in order to supply information regarding their structural particularities since the zinc role in biological environment, especially in the bone, is still under debate.XRD analysis confirmed the vitreous character of the as-prepared samples, while SEM and EDAX measurements indicated the presence of some non-homogeneous domains on their surfaces with approximately similar elemental composition. According to FTIR and Raman spectroscopy, the local structure of glasses up to 10 mol% ZnO is mainly built by Q² tetrahedrons connected by P–O–P linkages. For 50 mol% ZnO, the modifier role of zinc ions is strongly reflected on the local structure dominated in this case by Q¹ pyrophosphate units.The surface reactivity of the samples has been analyzed in vitro by immersion in simulated body fluid (SBF) at 37 °C. XRD, SEM–EDAX, FTIR and Raman methods were employed to characterize the structural changes that occurred on the surface of ZnO–CaO–P₂O₅ samples reacting with SBF. The X-ray diffraction patterns demonstrated the formation of a hydroxyapatite layer on the samples surface while the other used methods didn't reveal concisely that phenomenon. Based on X-ray measurements, the influence of zinc concentration on the hydroxyapatite layer development was followed.     

Laser transition characteristics of Nd3+-doped fluorophosphate laser glasses

Fluorophosphate glasses of composition P₂O₅–K₂O–MgO–Al₂O₃–AlF₃ and P₂O₅–K₂O–MgO–Al₂O₃–BaF₂ were prepared with different Nd³⁺ ion concentrations. The absorption and emission spectra in the UV–VIS–NIR region were measured for these glasses. Judd–Ofelt analysis has been carried out using the absorption spectra of 1.0 mol% Nd³⁺-doped glasses to evaluate the radiative properties for some luminescent levels of the Nd³⁺ ion. The stimulated emission cross-sections of the ⁴F_3/2 → ⁴I_11/2 laser transition for the present glasses are found to be higher than for other Nd³⁺-doped glasses. Branching ratio calculations also revealed the potentiality of the ⁴F_3/2 → ⁴I_11/2 transition for laser action in these glasses. The observed concentration quenching of the lifetime of the ⁴F_3/2 level is explained as a result of cross-relaxation process between the Nd³⁺ ions.