The structure and optical properties of GeO2-GeS2 glasses

Oxy-chalcogenide glasses with compositions of xGeO₂-(100 − x)GeS₂, where 0 ? x ? 100 mol%, have been prepared and studied in terms of their structures and optical properties. X-ray fluorescence spectroscopy shows that Ge:S ratio can deviate from GeS₂ by ∼10 at.%, depending critically upon the preparation conditions. Raman scattering spectroscopy suggests that stoichiometric GeO₂-GeS₂ glasses have a heterogeneous structure in the scale of 1-100 nm. The optical gaps are nearly constant at 3.0-3.5 eV for glasses with 0 ? x ? 80 mol% and abruptly increase to ∼6 eV in GeO₂. This dependence suggests that the optical gap is governed by GeS₂ clusters, which are isolated and/or percolated. Composition-deviated glasses appear as orange and brown, and these glasses seem to have more inhomogeneous structures.     

Glass formation in and structural investigation of Li2S + GeS2 + GeO2 composition using Raman and IR spectroscopy

Li₂S + GeS₂ + GeO₂ ternary glasses have been prepared and a wide glass-forming range was obtained. The glass transition temperatures increase with the GeO₂ concentration in the glasses. The vibrational modes of both bridging (Ge–S–Ge) and non-bridging (Ge–S⁻) sulfurs are observed in Raman and IR spectra of binary Li₂S + GeS₂ glasses. Additions of GeO₂ to this binary glass increase the bridging oxygen band (Ge–O–Ge) at the expense of decreasing the bridging sulfur band (Ge–S–Ge), whereas the bands associated with the non-bridging sulfurs (Ge–S⁻) remain constant in intensity up to high GeO₂ concentrations. At higher concentrations of GeO₂ (⩾60%), the non-bridging oxygen band, which is not observed at low and intermediate GeO₂ concentrations, appears and grows stronger. From these observations, it is suggested that the added lithium ions favor the non-bridging sulfur sites over the oxygen sites to form non-bridging sulfurs, whereas the added oxygen prefers the higher field strength Ge⁴⁺ cation to form bridging Ge–O–Ge bonds. The structural groups in the Li₂S + GeS₂ + GeO₂ glasses that are consistent with results of Raman and IR spectra are described and are used to develop a structural model of these glasses.     

Structural dependence of ultrafast third-order optical nonlinearity of Ge–Ga–Ag–S chalcogenide glasses

Ultrafast third-order optical nonlinearity of Ge–Ga–Ag–S chalcogenide glasses at the wavelength of 820 nm has been measured using femtosecond time-resolved optical Kerr (OKE) technique. The results show that Ge–Ga–Ag–S glasses have large third-order optical nonlinear susceptibility, χ⁽³⁾ and the response time is also subpicosecond, which are predominantly due to the ultrafast distortion of electron cloud surrounding the balanced positions of Ge, Ga, Ag and S atoms. What’s more, a strong dependence of χ⁽³⁾ on the composition and microstructure of these glasses was found which shows that [GeS₄] and [GaS₄] tetrahedra play an important role on the third-order optical nonlinearity. These Ge–Ga–Ag–S chalcogenide glasses would be expected as promising materials applied on all-optical switching devices.     

Far infrared transmission and structure of PbGeS semiconducting glasses

Lead sulfide has been found to form stable glasses with GeS₂ in the presence of GeS. Far-infrared transmission spectra of the glassy compositions x = 0.46, 0.23 and 0.115 in the pseudoternary (PbS)_x (GeS₂)_0.70?x (GeS)_0.30 and of the stoichiometric crystalline composition Pb₂GeS₄ have been observed for the first time. The results indicate a two optical mode behaviour of the compounds. The presence of the heavy lead atom in the GeS network seems to appreciably affect the bond bending modes of the GeS₄ molecular unit without significantly disturbing its bond stretching vibrations. The presence of S₃GeGeS₃ molecular units in the amorphous compositions and their absence in Pb₂GeS₄ are indicated.     

Effect of the substitution of S for Se on the structure and non-linear optical properties of the glasses in the system Ge0.18Ga0.05Sb0.07S0.70−xSex

Glasses in the system Ge–Ga–Sb–S/Se have been elaborated with different S/Se ratios in order to increase the non-linear optical properties of these glasses. We report results of a systematic study examining the relationship of the physical properties to the structure of the glasses in the system Ge_0.18Ga_0.05Sb_0.07S_0.70−xSe_x with x = 0, 0.02, 0.05, 0.10, 0.20, 0.30 and 0.40 where the replacement of S by Se has been made. The non-linear refractive index has been measured using the Z-scan technique, with picosecond pulses emitted by a 10 Hz Q-switched mode-locked Nd-Yag laser at 1064 nm under conditions suitable to characterize ultrafast non-linearities. The decrease of the glass transition temperature, the increase of the non-linear refractive index and of the density with the progressive replacement of S by Se have been correlated along with the red shift of the absorption band gap, to associated structural reorganization. A corresponding progressive decrease of corner-sharing GeS_4/2 and the formation of mostly two edge-sharing Ge₂S₄S_2/2, S₃Ge–S–GeS₃ as well as mixed GeS_4−xSe_x units have been identified by Raman spectroscopy.     

Glass formation, physico-chemical properties, and structure of glasses based on Ga2S3-GeS2-Sb2S3 system

We prepared sulfide glasses based on a Ga₂S₃-GeS₂-Sb₂S₃ system and investigated the compositional dependences of their physico-chemical properties and structure. Additivities were observed for density and refractive index; i.e., these properties were presented by the summation of the contribution from each component. With the increase of Sb₂S₃ content, the density, refractive index, and thermal expansion coefficient increased while the glass transition and softening temperatures decreased, and the short-wavelength absorption edge shifted to the longer wavelength side. These variations are expected from the incorporation of a heavy element (Sb) into the glasses. On the other hand, the replacement of GeS₂ by Ga₂S₃ increased the density and refractive index, and shifted the short-wavelength absorption edge to the longer wavelength side. These variations were explained by the increase of the number densities of the cations with the replacement and the formation of metal-metal bonds. The latter was confirmed from the Raman spectra. We also investigated the effects of Ag₂S incorporation on the optical properties. The incorporation of Ag₂S increased the density and refractive index whereas the position of the short-wavelength absorption edge varied little. These results show the possibility of fabricating an optical waveguide by Ag incorporation into the glasses.     

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.     

Structure and optical properties of amorphous GeSx films prepared by PLD

Amorphous GeS_x (x = 2, 4, 6) films were prepared by the pulsed laser deposition (PLD) technique. The optical band gaps (E_g^opt) and refractive indices of the films were obtained from the optical absorption spectra and transmission spectra, respectively. The short-wave absorption edges of the films were described using the ‘non-direct transition’ model proposed by Tauc. The dispersion of the refractive index was analyzed in terms of the single-oscillator Wemple–Di Domenico model. The structural units of the films were characterized using Raman spectroscopy. In addition to the basic structural units of edge-sharing and corner-sharing [GeS₄] tetrahedra, there are S–S homopolar bonds in S-rich GeS₄ and GeS₆ films while Ge–Ge bonds exist in stoichiometric GeS₂ film. The results show that the index of refraction decreases while E_g^opt increases with the sulphur content in the GeS_x films. The changes of E_g^opt were discussed in relation to the structure of GeS_x films, which were confirmed by the Raman spectra analysis.     

Behavior of Ag photodoping in sulfide bulk glasses

The relationship between Ag photodoping behavior and glass structure has been studied using various sulfide bulk glasses. The transmission measurement revealed that the photodoping rate increased with an increase of S concentration in Ge–S glasses and GeS₂–SbS₂ glasses, while the disappearance of Ag film was not be observed in Ge₄₀S₆₀ and Ga₂S₃-based glasses, which contain modifier ions. The correlation between photodoping rate and S–S bond content in a host glass was confirmed. From the point of view of the behavior of Ag photodoping, sulfide glasses were classified into two groups: (1) a covalent glasses containing S–S bonds and (2) an ionic glasses containing modified ions.     

Preparation and properties of chalcogenide glasses in the GeS2–Sb2S3–CdS system

In searching for new kind of photoelectric material, chalcogenide glasses in the GeS₂–Sb₂S₃–CdS system have been studied and their glass-forming region was determined. The system has a relatively large glass-forming region that is mainly situated along the GeS₂–Sb₂S₃ binary side. Thermal, optical and mechanical properties of the glasses were reported and the effects of compositional change on their properties are discussed. These novel chalcogenide glasses have relatively high glass transition temperatures (T_g ranges from 566 to 583 K), good thermal stabilities (the maximum of deference between the onset crystallization temperature, T_c, and T_g is 105 K), broad transmission region (0.57–12 μm) and large densities (d ranges from 2.99 to 3.34 g cm^?3). These glasses would be expected to be used in the field of rare earth doped fiber amplifiers and nonlinear optical devices.     

Microstructure and thermal properties of the GeS2–In2S3–CsI glassy system

A new series of chalcohalide glasses in the GeS₂–In₂S₃–CsI pseudo-ternary system were prepared by conventional melt-quenching method. The glass-forming region was determined and it is mainly situated in the GeS₂-rich domain. The glasses have relatively high glass transition temperatures (T_g ranges from 335 to 405 °C) and good thermal stabilities. Based on the Raman spectra, it can be speculated that the glassy net is mainly constituted by [GeS₄] and [InS_4?xI_x] tetrahedra, which are interconnected by the bridging sulfur atoms. And the ethane-liked structural units [S₃Ge–GeS₃] can be formed because of the lacking of sulfur. Cs⁺ ion, which was added from CsI, exists as the nearest neighbor of I^? ion.     

Preparation and characterization of glasses in the Ag2S + B2S3 + GeS2 system

The glass forming range of the Ag₂S + B₂S₃ + GeS₂ ternary system was investigated for the first time and a wide range of ternary glasses were obtained. The Archimedes’ method was used to determine the densities of the Ag-B-Ge glasses. The thermal properties of these thioborogermanate glasses were studied by DSC and TMA. The Raman, IR and NMR spectroscopy were used to explore the short-range order structure of the binary (Ag-B) and (Ag-Ge) and ternary (Ag-B-Ge) glasses. The results show the presence of bridging sulfur tetrahedral units, GeS_4/2 and AgBS_4/2, and trigonal units, BS_3/2, in the ternary glasses. Non-bridging sulfur units, AgSGeS_3/2 and Ag₃B₃S₃S_3/2 six membered rings, are also observed in these glasses at higher Ag₂S modification levels because the further addition of Ag₂S results in the degradation of the bridging structures to form non-bridging structures. The NMR studies show that Ag₂S goes into the GeS₂ subnetwork to form Ag₃S₃GeS_1/2 groups before going to the B₂S₃ subnetwork. In doing so, it is suggested that B₁₀S₂₀ supertetrahedra exist in Ag₂S + B₂S₃ and Ag₂S + B₂S₃ + GeS₂ glasses. Significantly B-S-Ge bonds form in the B₂S₃ + GeS₂ glasses, whereas they appear to be absent in the ternary glasses. From these observations, a structural model for these glasses has been developed and proposed.     

Third-order nonlinearity in Ag-nanoparticles embedded 56GeS2–24Ga2S3–20KBr chalcohalide glasses

Ag-nanoparticles were embedded in the 56GeS₂–24Ga₂S₃–20KBr chalcohalide glasses with varied doses by ion implantation. Ag-nanoparticles were observed in the AFM images of all implanted samples. The third-order optical nonlinearity of Ag-implanted chalcohalide glasses was investigated by the femtosecond Z-scan measurements. The results indicated an enhancement of third-order optical nonlinearity due to the formation of Ag-nanoparticles in glasses. The relation between implanting dose and third-order optical nonlinearity was strongly related to the intrinsic local field and interaction of Ag-nanoparticles.     

Observation of chemical reaction and liquid structure of SGe by Raman spectroscopy

The measurements of the Raman spectra on liquid Ge_XS_1?X (0≤X≤0.1) were carried out. The A₁ mode of $\text{GeS}{}_{\mathrm{<mtext>4</mtext><mtext>2</mtext>}}$ (ca. 340 cm^?1) was observed in the liquids. The comparison with the spectra of liquid S suggests that Ge reacts on the polymeric species. During the chemical reaction of solid Ge and liquid S below ca. 500°C, the L.T.GeS₂ crystal growth was observed. The spectral features of the L.T.GeS₂ surprisingly resemble those of GeS glasses. The glass forming region was extended to X = 0.03 by careful rapid quenching. The overall compositional dependence of the Raman spectra of Ge_XS_1?X (0.03≤×≤0.341) was analysed in comparison with the spectra of the L.T. and the H.T. crystal and can be explained by the model that with increase of X(>ca. 0.2) the H.T. GeS₂-like spectra emerge abruptly from the L.T.GeS₂-like spectra in lower X. Standing on the model, the glassy structures in this system are discussed.     

Ion conductive chalcohalide glasses in LiI–Ga2S3–GeS2 system

The electric properties of LiI containing chalcohalide glasses in the system Ga₂S₃–GeS₂ were studied by means of impedance spectroscopy and potentiostatic chronoamperometry. Two sets of the samples were prepared by direct synthesis from elements and compounds in evacuated quartz ampoules. The prepared glasses were as follows: xLiI–xGa₂S₃–(100?2x)GeS₂, x = 15, 20, 25 and 20LiI–xGa₂S₃–(80?x)GeS₂, x = 0, 5, 10, 15 and 20. In the first set the concentration of LiI increased and the second set was prepared to study the influence of Ga₂S₃ on the properties of the glasses. Additional aim of this work was to compare the electric properties of LiI containing Ga₂S₃–GeS₂ glasses with analogous AgI containing Ga₂S₃–GeS₂ glasses recently studied by us. The conductivity of the LiI containing glasses in the Ga₂S₃–GeS₂ system was higher and the activation energy was lower than in the analogous AgI containing system. The residual electronic (hole) conductivity remained similar in both systems being almost negligibly low. Raman spectroscopy proved the influence of LiI as well as Ga₂S₃ on glass structure, however interpretation of Raman spectra of these glasses is complicated due to small mass difference between gallium and germanium.     

Low-temperature Er3+ emission in Ge–S–Ga glasses excited by host absorption

The photoluminescence (PL) of a series of (GeS₂)₈₀(Ga₂S₃)₂₀ glasses doped with different amounts of Er (0.17, 0.35, 0.52, 1.05 and 1.39 at.%) at 77 and 4.2 K has been studied. The influence of the temperature on the emission cross-section of the PL bands at ∼1540, 980 and 820 nm under host excitation has been defined. A quenching effect of the host photoluminescence has been established from the compositional dependence of the PL intensity. It has been found that the present Er³⁺-doped Ge–S–Ga glasses posses PL lifetime values about 3.25 ms.     

Vacancy-induced densification of silica glass

We investigate vacancy-induced densification of silica glass using molecular dynamics simulations. Equilibration of defective glasses initially with various concentrations of vacancies yields glasses denser than the intact glass. The structural and vibrational properties of the densified glasses are characterized. Densification is related to structural changes induced by atomic rearrangement near vacancies, and increases with the concentration of vacancies. Vacancies may cluster and form voids, and the maximum densification for void-structured glasses occurs at a critical radius of about 0.44 nm. The glasses densified by vacancies and by simulated UV-laser irradiation display nearly identical structural and vibrational properties. These results appear to support the Douillard–Duraud point defect model as a common mechanism for radiation densification of silica glass.     

Compositional effects on fluorescence lifetime of Dy3+ ions embedded in chalcogenide Ge–As–S glasses containing very small amount of Ga and CsBr

We have investigated the fluorescence lifetimes of Dy³⁺: 1.3 μm emission in the chalcogenide Ge–As–S glasses with different compositions but identically containing 0.5 mol% Ga and 0.5 mol% CsBr. The measured lifetimes turn out to be sensitive not only to the concentrations of Ga and CsBr but also to compositional variations in the Ge–As–S host glasses. The lifetime is enhanced conspicuously in glass of the S-sufficient compositions, relative to the stoichiometric GeS₂–As₂S₃ composition, while this effect is not significant in the S-exact and S-deficient compositions. We employ Ga K-edge EXAFS analysis to support that the local structural environments of Ga in the modified chalcogenide glasses are closely correlated with the lifetime enhancement effect.     

Raman spectra of GeSbS system glasses in the S-rich region

Raman spectra of the Ge_xSb_yS_z glasses with sulfur concentration ?65 at.% are given and discussed. From the obtained Raman spectra it is concluded that the presence of small concentrations of Ge atoms of more than the (GeS₂)_1?x(Sb₂S₃)_x compositions results in the formation of S₃GeGeS₃ structural units. On the other hand the presence of small concentrations of excess sulfur results in replacing some individual bridging S atoms by ?SS? bridging groups. At higher concentrations of the excess sulfur the S atoms form S₈ ring molecules which are dissolved in the network structure of the glass composed of GeS₄ tetrahedra and SbS₃ pyramids interconnected by one or two sulfur atoms.     

The structure of densified As2O3 glasses

In situ high energy X-ray diffraction and Raman experiments have been carried out to probe the structure changes of vitreous As₂O₃ under pressure. The first sharp diffraction peak reduces in intensity up to 10 GPa, indicating a breakdown of intermediate range order with pressure. All features in the Raman spectra broaden with increasing pressure up to 11.6 GPa. The mode at 378 cm⁻¹ associated with As₄O₆ molecule-like vibrations increases in intensity up to 6.2 GPa and decreases at higher pressures. In addition, X-ray and neutron structure factors have been measured for normal density and permanently densified As₂O₃ glasses recovered from 10 and 23 GPa. The results show the local AsO₃ pyramids and 3-membered rings essentially remain intact after compression. The increase in density is mainly associated with an inward shift of the third nearest neighbor peak in the X-ray radial distribution function, which indicates an increased packing of 3-membered AsO₃ rings.