Optical and structural properties of new chalcohalide glasses

New class of chalcohalide glasses has been prepared in the GeS₂–In₂S₃–CsI system with regard to their potential non-linear properties. The study of glass-forming region was undertaken to select glassy compositions, which present high non-linear (NL) optical properties with a low two-photon absorption. Thermal analyses, structural examination by Raman spectroscopy, non-linear optical measurements were investigated as a function of CsI contents. Introduction of CsI has shifted the band-gap edge towards the blue region of the absorption optical spectrum and therefore has limited the two-photon absorption. Their NL refractive index n₂ are 60 times higher than silica glasses without any NL absorption. Moreover, second harmonic signal was observed in thermally poled samples similar to silica glass. However, this second order non-linearity is not temporally stable.     

Ab initio calculation of chain structures in chalcohalide glasses

Local structure of Te₃X₂ (X = Cl, Br) chalcohalide glasses were studied using ab initio molecular orbital (MO) theory. The calculation results were compared with Mössbauer spectroscopic parameters in terms of electric-field gradient and electron density at each Te site. In addition, the existence of terminal bond –Te–X was examined. The MO analysis of Te-chain and Te-chain with Cl atoms within a picture of the frontier orbital theory elucidated that the localized orbital at –TeCl₂– site is important to form tellurium halide glass.     

The study of Sm3+-doped low-phonon-energy chalcohalide glasses

The Sm³⁺-doped low-phonon-energy (LPE) Ge–Ga–Se–CsI glasses were studied. Upon excitation at 980 nm diode laser, intense 1.25 and 1.49 μm near-infrared fluorescence bands with broad full width at half maximum (FWHM) of 49 and 53 nm were observed, respectively. About 180–300 μs fluorescence lifetimes were obtained for the 1.49 μm emission. The thermal properties and structure of glasses were investigated by differential thermal analysis (DTA) and Raman spectra, respectively. Spectroscopic characteristics of the optical transitions have been calculated by using the Judd–Ofelt theory and evaluated for excited levels.     

Structure and optical properties of chalcohalide glasses doped with Pr and Yb ions

Glasses of systems 100-y((GeS₂)₈₀(Sb₂S₃)_20−x(PbI₂)_x)yPr₂S₃, x = 0; 2; 5, 8; y = 0; 0.01; 0.1; 0.5 and 99.9-z((GeS₂)₈₀(Sb₂S₃)₁₈(PbI₂)₂)0.1Pr₂S₃zYb₂S₃, z = 0.05; 0.1; 0.15) were synthesized in high purity. Optically well transparent glasses were obtained for x  5 mol.% PbI₂, for y  0.1 mol.% Pr₂S₃ and for z  0.15 mol.% Yb₂S₃. The glasses were stable and homogeneous, as confirmed by X-ray diffraction and electron microscopy, with high optical transmittivity from visible (red) region up to infrared region (900 cm⁻¹). The density of the glasses was 3.26–3.33 gcm⁻³ for PbI₂ containing glasses. The glass transition temperature, T_g, was 320–336 °C. The optical absorption bands in rare-earth doped glasses corresponded to ³H₄–³F₄, ³H₄–³F₃, ³H₄–(³F₂ + ³H₆) f–f electron transitions of Pr³⁺ ions and to ²F_7/2–²F_5/2 f–f electron transitions of Yb³⁺ ions. Strong luminescence band with maximum near 1340 nm (electron transition ¹G₄–³H₅) was found in Pr₂S₃ doped glasses. The intensity of this band was rising with doping by Yb³⁺ ions. The possible mechanism of the luminescence enhancement is suggested.     

Aging of oriented polymer glasses

Dimensional (D) and enthalpy relaxation (ΔH) of oriented polymer glasses (PS and PC) have been studied as function of temperature, between T_g and T_g−20 °C, and aging time t, ranging to several weeks. The dimensional relaxation (shrinkage) and enthalpy relaxation curves verify the logarithm law D(t) ∼ H(t) ∼ log t, between an incubation τ_i and a final relaxation time τ_f. The time τ_f to reach the equilibrium (D and ΔH) follows the Vogel–Tamann–Fulcher (VFT) law. Enthalpy relaxation and shrinkage exhibit important differences. Enthalpy relaxation of oriented and isotropic polymers follows the same logarithm law, independent of the draw ratio λ and the mode of deformation, the relaxation time τ_f coincides with the relaxation time of the α segmental motions. Shrinkage depends on λ and the mode of deformation, the relaxation time τ_f is attributed to the normal mode, the relaxation time of the whole chain. Finally the shrinkages of PS and PC show some differences. PC at short aging times presents another type of dimensional relaxation which would be due to the β motions. This would be in close connection with the ductile (PC) and fragile (PS) behavior of these two polymers far below T_g.     

Local structure and its effect on the oscillator strengths and emission properties of Ho in chalcohalide glasses

The formation of structural units in Ge-Ga-S glass with CsBr addition and its effect on the optical band gap and several spectroscopic properties of Ho³⁺ were investigated. The optical band gap of the host glasses and the oscillator strengths of Ho³⁺ absorption decreased sharply when the ratio of CsBr/Ga became close to unity. These property changes were associated with the formation of structural units of [GaS_3/2Br]⁻ and they have a crucial effect on the changes of the local structure around Ho³⁺ ions. The local structure was not sensitive to the As or Br addition but was critically dependent on the concentration of CsBr.     

H2O influence evaluating and mid-IR fluorescence quenching in Tm3+-doped GeGaSCsI chalcohalide glasses

This work presents a detailed study on near-infrared and mid-infrared fluorescence emissions with five sets of Tm³⁺-doped 75GeS₂–15Ga₂S₃–10CsI chalcohalide glass. They are prepared in normal or water drying process. Based on the diffusion-limited relaxation calculation, a detailed investigation is put forward to obtain efficient near-infrared or mid-infrared fluorescence emissions of Tm³⁺ on the effect of H₂O on the Tm³⁺ fluorescence. Detailed investigations are given to the interacted energy transferring processes between rare-earth, impurities and vibrating phonons with the appearance of fluorescence quenching, along with Tm³⁺, H₂O concentrations varying and energy gaps forming. The radioactive properties are analyzed using compensated diffusion-limited relaxation calculation method, and the near-IR and mid-IR fluorescence properties are evaluated in detail with experimental and theoretical analysis.     

Compositional dependences on the mechanism of upconversion in Nd3+/Tm3+ co-doped chalcohalide glasses

Mechanisms of the compositional dependence of blue emission from Nd³⁺/Tm³⁺ co-doped Ge–Ga–S–CsBr chalcohalide glasses were investigated. The blue upconversion emissions (centered at 475 nm) due to the Tm³⁺: ¹G₄ → ³H₆ transition decreased as the CsBr/Ga ratio in glasses while the other upconversion emissions from the Nd³⁺ ions increased. Changes in the local environment of rare-earth ions incurred by the CsBr addition significantly increased the excited state absorption within Nd³⁺ ions. This resulted in the decrease in the Nd³⁺ → Tm³⁺ energy transfer rates that led to the large decrease in blue upconversion emission.     

Luminescence behaviors of the Eu2+ ions in the GeS2-Ga2S3-CsCl chalcohalide glasses

In the paper, we report the luminescence behaviors of Eu²⁺-doped chalcohalide glasses. Composition of glass matrix is 37.5GeS₂-22.5Ga₂S₃-40CsCl (mol%) with the concentration of Eu²⁺ in the range of 0.1–0.25 (mol%). The optimal Eu²⁺ doping concentration was 0.15 mol% at which the glass exhibited an enhanced emission peaking at 434 nm with a full width at half maximum (FWHM) about 80 nm with the excitation at 395 nm.     

Origin of blue and green colouration in sulphur containing alkali borate glasses

Simple binary sodium and potassium borate glasses containing sulphur were prepared. Depending on the composition of the glass and the quantity of sulphur added the glasses produced were blue, green or yellow. The absorption spectra of these glasses were measured in the range of 300–700 nm.The blue colour is characterized by an absorption band at 585 nm which is attributed to S₃^?.The green colour is characterized by two absorption bands; the band at 585 nm observed in the spectra of the blue glasses and a more intense band at 390 nm. The latter is attributed to S₂^? and the green colouration to the presence of both S₂^? and S₃^? where the S₂^? state predominates.     

Origin of boson peak in glasses: Role of Ioffe–Regel crossover and atomic soft modes

A theoretical ‘complete soft-mode-dynamics’ model of the origin and properties of the boson peak accompanied by a high-frequency sound, observed in glasses of a certain type, is described. The origin is determined by interaction of non-acoustic vibrations with acoustic phonons and a Ioffe–Regel crossover for their inelastic scattering. The non-acoustic excitations are associated with vibrations of atomic soft-mode ‘defects’. Two types of boson peak can be predicted in agreement with experiments.     

Glassy states: Concentration glasses and temperature glasses compared

The behavior of glass-forming systems in the equilibrium state above the glass temperature is still a heavily investigated field. Surprisingly, the behavior of the glass itself is less widely investigated. Even less investigated is the behavior of glass-forming materials in which composition is changed. Here we look at the behavior of glasses after temperature-jumps and compare that behavior with that of glasses subjected to concentration-jumps. Moisture and carbon dioxide are used as the plasticizing environments. Surprisingly, the glass created by jumping (down) to a given final condition via a change in concentration is more stable than that formed by a change in temperature – this in spite of the external condition of temperature and chemical activity (RH or carbon dioxide pressure) being the same. Furthermore, the concentration glass under such conditions has a higher excess volume than the temperature glass and its response does not ‘merge’ with that of the temperature glass, hence, the concentration glass is not the same as a temperature hyperquenched glass.     

1.48 μm emission properties and the cross-relaxation mechanism in chalcohalide glass doped with Tm

1.48 μm emission properties and the cross-relaxation mechanism of Tm³⁺ ions in 0.7(Ge_0.25As_0.10S_0.65) + 0.15GaS_3/2 + 0.15CsBr glass were investigated. Both the relative intensity ratio of the 1.48 μm emission to 1.82 μm and the measured lifetime of the ³H₄ level decreased with increasing Tm³⁺ concentration. When temperature decreased from room temperature to 20 K, lifetimes of the ³H₄ level increased from 670 to 970 μs. At the same time, the critical distance for cross-relaxation decreased from 1.11 to 0.93 nm. These results indicate that cross-relaxation (³H₄, ³H₆ → ³F₄, ³F₄) became less effective as temperature decreased. Analysis of the temperature dependence of cross-relaxation rates showed that cross-relaxation in Tm³⁺ is a phonon-assisted energy transfer process. The major phonon contributing to the process is from the Ga-Br vibration in [GaS_3/2Br]⁻ units.     

Aging,glass transition,supercooled and equilibrium liquid states of alkali germanate glasses studied by Brillouin scattering

The elastic properties of alkali germanate glasses, xR₂O?(100 ? x)GeO₂ (R = Li, Na, K, Rb, Cs ; x = 14, 28), have been studied by Brillouin scattering in the wide temperature range up to 1200 °C. The remarkable aging effect of Brillouin shift Δν_L has been observed below a glass transition temperature T_g ≈ 500 °C. The temperature dependence of longitudinal sound velocity V_L of well annealed glasses shows the gradual decrease below T_g, while on further heating the remarkable decrease is observed above T_g. The scaled temperature dependence of V_L is nearly independent on alkali metals below the melting temperature T_m. While on further heating above T_m, the drastic decrease of V_L and increase of α_L show the remarkable alkali dependence. It may be attributed to the appearance of dynamic process related to ionic hopping of alkali metals released from glass network above T_m.     

Vibrational modes and structure of (AgI)x (GeS1.5)100−x chalcohalide glasses

We report a structural investigation of bulk Ge-rich Ge–S–AgI chalcohalide glasses. A vibrational spectroscopic study of the quaternary system (AgI)_x (GeS_1.5)_100−x (0  x_AgI  20) has been undertaken using infrared spectroscopy and Fourier transform Raman scattering. It was found that the GeS_1.5 Raman spectrum is compatible with a glass structure composed of corner- and edge-sharing mixed GeS_nGe_4−n (n = 0–4) tetrahedra where units with n = 2–4 dominate, whilst the fraction of corner-sharing units are significantly lower than the corresponding fraction in the stoichiometric GeS₂ glass. The addition of AgI has revealed a subtle but systematic effect in the structure of the Ge-rich glass matrix, manifested by mild decrease of the ES units and the concomitant increase of complex GeS_nI_4−n or GeS_nGe_mI_4-n−m tetrahedra whose vibrational modes form a continuum at low frequencies. Although, AgI seems to cause subtle structural changes due to the formation of Ge–I bonds, it is also evident that AgI does not act as a real modifier that would depolymerize appreciably the Ge–S network structure.     

Li conductivity in lithium niobate: silica glasses

Glasses of composition 65 mol% LiNbO₃:: 35 mol% SiO₂ have been shown to be Li⁺ ion conductors with a conductivity at 200°C > 1 × 10⁻⁵ (η cm)⁻¹ and an activation energy of 0.54 eV. The addition of approximately 0.1 mol% Fe₂O₃ leads to an enhancement of conductivity to ≈10⁻³ (η cm)⁻¹ at 200°C and an activation energy of 0.67 eV. The effect of Fe is shown to be in the control of microstructure in the glass, with Fe₂O₃ concentrations < 1 mol% acting as a grain growth inhibitors and larger concentrations acting as a nucleating agents. A model for this process based on the expected stoichiometry of the melt and the effect of Fe²⁺ and Fe³⁺ in charge compensation is in excellent agreement with experimental data from electron spin resonance.     

Water diffusion in silicate glasses under natural weathering conditions: evidence from buried medieval stained glasses

In this study, ion-microprobe analyses of four samples of buried medieval stained-glasses are used to demonstrate that water penetrates into the matrix of pristine glasses at low temperatures, thereby showing that glass alteration is not only a surface process. The diffusion coefficients of water determined from concentration profiles of hydrogen are found to be correlated with the bulk polymerization state of the glass. This observation is discussed with respect to glass structure and implies that ionic exchange between hydrogen and network modifying metal cations is the major process responsible for glass hydration.     

Defects in specialty and container glasses

Laboratory techniques used to identify solid inclusions such as stones cords, and knots in glass will be described. Examples of defects from raw material, refractory, devitrification and miscellaneous sources will be presented. Glass melting, liquidus determination techniques, and glass-refractory corrosion testing methods can all be utilized to better define defect sources. Correlations between these laboratory tests and actual stone defects will be made.