Effect of gallium addition on physical and structural properties of Ge–S chalcogenide glasses

GeS_2.5 chalcogenide glass was selected for studying effects of Ga addition on physical and structural properties. Glassy and partially crystallized samples of (100−x)GeS_2.5−xGa (5 mol% ≤ x ≤ 40 mol%) were prepared, and their thermal and optical properties were characterized. With increasing Ga content (x), values of T_g and optical band gap of glasses initially increased and then decreased, showing a maximal value at x = 25 mol%, that is, with stoichiometric composition of 85.7GeS₂·14.3Ga₂S₃. These changes were discussed and correlated to evolution of network structure, which was investigated by Raman spectra recorded in glassy matrices of (100−x)GeS_2.5−xGa (5 mol% ≤ x ≤ 40 mol%). This work contributes to understanding of composition–structure–property relationship of chalcogenide glasses.     

The Effect of PbS on Crystallization Behavior of GeS2‐Ga2S3‐Based Chalcogenide Glasses

Glass‐ceramics of PbS‐doped 80GeS₂·20Ga₂S₃ were fabricated by heat treatments of base glasses at T_g+30°C for different durations. They exhibited improved mechanical properties such as hardness and resistance to crack propagation, and meanwhile retained their excellent infrared transmission. X‐ray diffraction and Raman results indicated that Ga₂S₃ and GeS₂ crystals were precipitated inside glassy matrix. The crystallization kinetics of base glass was investigated using differential scanning calorimetry under nonisothermal conditions. Compared with the previous work concerning on 80GeS₂·20Ga₂S₃ glass, there exists some different features of crystallization behavior. Such variation is discussed and correlated with the network structure and crystallization kinetics in this glass system.     

Phase Separation in Nonstoichiometry Ge–Sb–S Chalcogenide Glasses

A series of (1 ? x)GeS_2.5 – xSb chalcogenide glasses were prepared using the conventional melt‐quenching method. Their microstructure and thermal response were systematically studied. We observe a compositional threshold of x = 0.25 which corresponds to chemical stoichiometric composition in the calorimetric experiments. It is in good accordance with the Raman scattering results and laser‐induced phase transformation behavior. They also indicate that phase separation of Sb‐rich phase exists in the S‐poor samples. Moreover, we got a structural modeling of this phase separation: (1) at x = 0.25, which is chemical stoichiometric composition, the structural motifs are only SbS₃ pyramid and GeS₄ tetrahedra, and the three‐coordinated SbS₃ pyramid is isolated by GeS₄ tetrahedra; (2) at x < 0.25, the S–S bonds exist in the glass network due to the excess of S; and (3) at x > 0.25, the excess of Sb break the Ge–S and Sb–S bonds to form Sb(Ge)–Sb Bonds, and the Sb atoms segregate from the backbone to nucleate a separate Sb‐rich phase. This work provides a new way to investigate the phase separation of glass networks and helps us to better understand their related physical properties.     

First Identification of Rare‐Earth Oxide Nucleation in Chalcogenide Glasses and Implications for Fabrication of Mid‐Infrared Active Fibers

Gallium (Ga) helps solubilize rare‐earth ions in chalcogenide glasses, but has been found to form the dominant crystallizing selenide phase in bulk glass in our previous work. Here, the crystallization behavior is compared of as‐annealed 0–3000 ppmw Dy³⁺‐doped Ge–As–Ga–Se glasses with different Ga levels: Ge_16.5As_(19?x)Ga_xSe_64.5 (at.%), for x = 3 and 10, named Ga₃ and Ga₁₀ glass series, respectively. X‐ray diffraction and high‐resolution transmission electron microscopy are employed to examine crystals in the bulk of the as‐prepared glasses, and the crystalline phase is proved to be the same: Ge‐modified, face centered cubic α‐Ga₂Se₃. Light scattering of polished glass samples is monitored using Fourier transform spectroscopy. When Ga is decreased from 10 to 3 at.%, the bulk crystallization is dramatically reduced and the optical scattering loss decreases. Surface defects, with a rough topology observed for both series of as‐prepared chalcogenide glasses, are demonstrated to comprise Dy, Si, and [O]. For the first time, evidence for the proposed nucleation agent Dy₂O₃ is found inside the bulk of as‐prepared glass. This is an important result because rare‐earth ions bound in a high phonon–energy oxide local environment are, as a consequence, inactive mid‐infrared fluorophores because they undergo preferential nonradiative decay of excited states.     

Controllable Formation of the Crystalline Phases in Ge–Ga–S Chalcogenide Glass‐Ceramics

We prepared chemically stoichiometric, S‐poor and S‐rich Ge–Ga–S glasses and annealed them at a temperature that was 20°C higher than its respective glass transition temperature. We aimed at tuning the formation of the different crystals in chalcogenide glass‐ceramics. Through systematic characterization of the structure using X‐ray diffraction and Raman scattering spectra, we found that, GeS₂ and GeS crystals only can be created in S‐rich and S‐poor glass‐ceramics, respectively, while all GeS, Ga₂S₃, and GeS₂ crystals exist in chemically stoichiometric glass‐ceramics. Moreover, we demonstrated the homogeneous distribution of the crystals can be formed in the S‐rich glass‐ceramics from the surface to the interior via composition designing. The present approach blazes a new path to control the growth of the different crystals in chalcogenide glass‐ceramics.     

Glass Formation and Ionic Conduction Behavior in GeSe2–Ga2Se3–NaI Chalcogenide System

Series of glassy and glass‐ceramic samples in the GeSe₂–Ga₂Se₃–NaI system is prepared by melt‐quenching technique and the glass‐forming region is well‐defined by XRD investigations. Na‐ion conduction behavior is systemically studied by impedance measurements. For the glasses in the series (100?2x)GeSe₂–xGa₂Se₃–xNaI, ionic conductivities increased with increasing x, whereas the attributed activation energy of ion conduction decreases. The enhanced mechanism is discussed by employing Raman spectra. In addition, the effect of the crystal phases NaI and Ga₂Se₃ on the ionic conduction behavior in the (70?x)GeSe₂–xGa₂Se₃–30NaI samples is discussed. Although it shows that the poorly conducting crystallites of NaI and Ga₂Se₃ have a negative effect on the ionic conductivities in this series, the highest ionic conductivity of 1.65 × 10^?6 S/cm is obtained in the 45GeSe₂–25Ga₂Se₃–30NaI glass. Finally, this study also demonstrates a possible way to search appropriate Na‐ion solid electrolytes for all‐solid‐state batteries.     

Compositional dependence of the optical properties of novel Ga–Sb–S–XI (XI = PbI2, CsI,AgI) infrared chalcogenide glasses

A novel family of Ga₂S₃–Sb₂S₃–XI (XI = PbI₂, CsI, AgI) was investigated to understand the role of metal halides and exploit new chalco‐halide glasses for infrared optics. The dependence of the thermal properties, infrared optical properties, and structural information of the novel family on different metal–iodines was investigated. Results showed that metal halides increase the glass stability but decrease the glass network connectivity. The compositional dependence of the short‐wave cut‐off edge is associated with the electronegativity difference between the cations and anions of the metal halides. Raman study showed that the metal–iodine modified the glass structure mainly through the iodide content, and the cations dissolved in the glass network mostly as charge compensators for the aperiodic network. For the glasses in the series Ga₂S₃–Sb₂S₃–XI–Dy³⁺, Dy³⁺ emission increased in the PbI₂‐ and CsI‐doped glasses but decreased in the AgI‐doped glass due to the combined effect of dysprosium and oxygen. For all that, these novel glasses are highly promised for use in infrared optics.     

Effective ionic transport in AgI-based Ge(Ga)–Sb–S chalcogenide glasses

AgI-based Ge–Sb–S, Ga–Sb–S, and Ge–Ga–Sb–S chalcogenide glasses were designed and prepared by melt-quenching, thereafter their thermal properties and conductive performance were comparatively investigated on the basis of their composition-induced network structures. Glass transition in each sample was examined by DSC measurements. Results showed that the samples containing Ge had a higher thermal stability than the Ga–Sb–S–AgI sample, and the Ge–Sb–S–AgI sample obtained had the highest conductivity ion. Raman spectrum analysis was performed, and the results indicated that the [GeS_4-xI_x] structural units and [SbS_3−xI_x] pyramids in the matrix produced effective ion transport channel for dissolved conductive Ag⁺ ions. In the matrix containing Ga, the [Ga(Ge)S_4-xI_x] structure was consumed by part of [S₃Ga–GaS₃] ethane-like units, which had no contribution to the ion transition framework. The study provided the directions for composition and structure configuration control in effective conductive chalcogenide glasses.     

Enhanced Up‐Conversion Luminescence in Er3+‐Doped 25GeS2·35Ga2S3·40CsCl Chalcogenide Glass–Ceramics

Enhanced luminescence in rare‐earth‐doped chalcogenide glass–ceramics is of great interest for the potential integrated optoelectronic devices. However, fundamental mechanism on the enhancement of luminescence upon crystallization remains largely unknown. We report the fabrication and characterization of wide transmission chalcogenide glass and glass–ceramics based on the 25GeS₂·35Ga₂S₃·40CsCl:0.3Er glass composition, and discuss the mechanism of enhanced luminescence. By monitoring the ⁴I_9/2–⁴I_15/2 of Er³⁺ transition, up‐conversion luminescence of 12 times higher was observed in glass–ceramics compared with that in base glass. Electron paramagnetic resonance (EPR) and Raman scattering spectroscopies were employed to obtain the information of selective environment of Er³⁺ ions and microstructural evolution with the crystallization progress. Both of them evidenced that the enhanced up‐conversion luminescence was mainly related to the local environmental evolution from a mixed chlorine‐sulfur coordination to a low phonon energy chlorine coordination in the residual glassy matrix of glass–ceramics.     

Dy3+‐Doped Selenide Chalcogenide Glasses: Influence of Dy3+ Dopant‐Additive and Containment

This work reports on process‐induced impurities in rare‐earth ion: Dy³⁺‐doped selenide chalcogenide glasses, which are significant materials for active photonic devices in the mid‐infrared region. In particular, the effect of contamination from the silica glass ampoule containment used in chalcogenide glass synthesis is studied. Heat‐treating Dy‐foil‐only, and DyCl₃‐only, separately, within evacuated silica glass ampoules gives direct evidence of silica ampoule corrosion by the rare‐earth additives. The presence of [Ga₂Se₃] associated with [Dy] on the silica glass ampoule that has been contact with the chalcogenide glass during glass melting, is reported for the first time. Studies of 0–3000 ppmw Dy³⁺‐doped Ge_16.5As₉Ga₁₀Se_64.5 glasses show that Dy‐foil is better than DyCl₃ as the Dy³⁺ additive in Ge‐As‐Ga‐Se glass in aspects of avoiding bulk crystallization, improving glass surface quality and lowering optical loss. However, some limited Dy/Si/O related contamination is observed on the surfaces of Dy‐foil‐doped chalcogenide glasses, as found for DyCl₃‐doped chalcogenide glasses, reported in our previous work. The surface contamination indicates the production of Dy₂O₃ and/or [≡Si‐O‐Dy=]‐containing particles during chalcogenide glass melting, which are potential light‐scattering centers in chalcogenide bulk glass and heterogeneous nucleation agents for α‐Ga₂Se₃ crystals.     

Formation of Ferroelectric Phases in Sb–S–I Glasses

We have investigated devitrification of glasses within infrared transmitting xSbSI–(100 ? x)Sb₂S₃ pseudo‐binary series, which forms SbSI and Sb₂S₃ ferroelectric crystal phases. Differential scanning calorimetry (DSC) and X‐ray powder diffraction results show unusual behavior for the formation of the SbSI phase, which occurs by two parallel processes: one‐dimensional crystallization at low temperature which starts from the sample surface, and three‐dimensional bulk crystallization that continues the transformation to crystalline state at higher temperatures. The ratio of the intensities of the high‐temperature exothermal peak to the low‐temperature peak in DSC scans increases as the particle size and heating rate are increased. In contrast to the SbSI phase, the temperature of crystallization for the Sb₂S₃ phase does not depend on the particle size. Models are proposed for the origin of the various crystallization mechanisms.     

Infrared GRIN GeS2–Sb2S3–CsCl chalcogenide glass–ceramics

Chalcogenide glasses show a unique potential for creating gradient refractive index (GRIN) lenses, which would reduce the size and weight of infrared thermal imaging system and remain/improve its performance. Here, we propose a new method that forms a GRIN chalcogenide glass–ceramics (GCs) by creating low refractive index (n) CsCl nanocrystals within a high n GeS₂–Sb₂S₃ glass matrix. After specific gradient thermal treatment, the GRIN structure of Δn ∼ 0.04 was formed through the gradient precipitation of CsCl. This work would pave a new path to design the GRIN chalcogenide GCs through a selective crystallization of halide crystals with low n.     

Competitive Phase Separation to Controllable Crystallization in 80GeS2·20In2S3 Chalcogenide Glass

Glass–ceramics of 80GeS₂·20In₂S₃ were fabricated by heat‐treating the base glass at 402°C (T_g + 30°C) for different durations. The glass–ceramics exhibited some improved mechanical properties such as hardness and resistance to crack propagation, and meanwhile remained an excellent infrared (IR) transmission. The XRD and Raman results showed that only In₂S₃ crystals were precipitated inside glassy matrix. The evolution of two crystallization peaks (CPs) in differential scanning calorimeter (DSC) curves were studied with samples heat‐treated at 402°C for different durations. It was found that the precipitation of In₂S₃ crystal phase is responsible for the low‐temperature (first) CP, whereas the high‐temperature (second) CP shifts to a higher temperature with the elongation of the heat‐treatment duration. The crystallization of the higher temperature phase was inhibited with the precipitation of In₂S₃. Furthermore, crystallization mechanism was investigated using the nonisothermal method. The computed results showed that strictly more energy (higher activation energy, E_c) is essential for the precipitation of the higher temperature phase, which is in accordance with the DSC study of crystallized samples. More noticeable, the crystallization rate constant (K) value of 6.639 × 10^?8 s^?1 for the second CP is ~ 5 orders of magnitude smaller than that of the In₂S₃ phase, and this significant difference makes the crystallization of higher temperature crystal phase very hard. Consequently, controllable crystallization of 80GeS₂·20In₂S₃ chalcogenide glass–ceramics with sole In₂S₃ crystallites can be achieved easily.     

Ga2S3‐Sb2S3‐CsI chalcohalide glasses for mid‐infrared applications

In this study, a new chalcohalide glass system, Ga₂S₃‐Sb₂S₃‐CsI, is reported. It has a glass‐forming domain composed of ~0‐35 mol% Ga₂S_3, ~15‐95 mol% Sb₂S₃, and ~0‐55 mol% CsI. The glasses have a wide transparent window of ~0.7‐13.5 μm, high third‐order nonlinear refractive indices of ~1.7‐8.7×10^?14 cm²/W @ 1.55 μm, and relatively short zero group‐velocity‐dispersion wavelengths of 3.8‐5.15 μm. The glasses can dissolve more than 2 mol% active ions (e.g., Dy³⁺), and the doped glasses show intense emissions in the mid‐infrared. These superior properties demonstrate their good potentials for mid‐infrared applications such as thermal imaging, nonlinear photonics and lasers.     

Fabrication and microstructure of perovskite CsPbCl3 nanocrystallized chalcogenide glass-ceramics

Transparent chalcogenide glass-ceramics containing CsPbCl₃ perovskite nanocrystals were prepared through an elaborated composition design of 80GeS₂·5Ga₂S₃·15CsPbCl₃. Large size distribution of CsPbCl₃ nanocrystals is observed ranging from 10 to 200 nm. XRD, Raman spectra, and SEM techniques were employed to study the further microstructural evolution after thermal treatment. The precipitation of PbGeS₃ and GeS₂, together with CsPbCl₃, was identified according to the XRD patterns and Raman spectra. This work is of guiding significance for future design of cesium lead halide perovskite nanocrystals in chalcogenide glass-ceramics.     

Design and magneto-optical characteristics of Ge–Sb–S–PbI2 chalcogenide glasses with a high Verdet constant

To develop high-performance magneto-optical chalcogenide glasses and clarify the mechanisms of the Verdet constant, a series of GeS₂–Sb₂S₃–PbI₂ chalcogenide glasses were designed and fabricated, and their Faraday effects were investigated at a wavelength of 980 nm. A new parameter, that is, average polarizability, was proposed, and the results show that the Verdet constant has a good linear relationship with average polarizability, meaning that the Verdet constant of a chalcogenide glass can be directly estimated by its chemical constituents. The Verdet constant is as large as 0.200 min G⁻¹ cm⁻¹ at 980 nm for 22.5GeS₂–67.5Sb₂S₃–10PbI₂ composition glass, which is the largest value reported thus far for sulfide glasses; this glass also possesses good thermal and optical properties and therefore might be an attractive candidate for mid-infrared magneto-optical device applications.     

Preparation and properties of Ge–Ga–La–S–AgI chalcogenide glass

Chalcogenide glasses of 65GeS₂–(25–x)Ga₂S₃–10AgI–xLa₂S₃ (x=0, 1, 3, and 5 mol%) were fabricated through the traditional melt-quenching method. The effects of addition of La₂S₃ on physical, thermal and optical properties of the glass system were investigated. The results showed that the fabricated glasses possess considerably high glass transition temperature, exhibit improved mechanical property and excellent infrared transmission. A redshift at the visible absorbing cut-off edge is observed with increasing of La₂S₃ content. The direct and indirect optical band gap values are also calculated. Raman spectra analysis indicated that the band at 265 cm⁻¹ decreased in amplitude and a new peak at 230 cm⁻¹ was detected manifesting the formation of La-S bond in the network. In addition, the mid-infrared emission at 3.74 µm of the glasses doped with Tm³⁺ ions was achieved. The results indicated that the glasses are promising materials for mid-infrared applications such as imaging, remote sensing and lasers.     

Thermal and optical properties of La2O3–Ga2O3– (Nb2O5 or Ta2O5) ternary glasses

La₂O₃–Ga₂O₃–M₂O₅ (M = Nb or Ta) ternary glasses were fabricated using an aerodynamic levitation technique, and their glass‐forming regions and thermal and optical properties were investigated. Incorporation of adequate amounts of Nb₂O₅ and Ta₂O₅ drastically improved the thermal stabilities of the glasses against crystallization. Optical transmittance measurements revealed that all the glasses were transparent over a wide wavelength range from the ultraviolet to the mid‐infrared. The refractive indices of the glasses increased and the Abbe number decreased upon substituting Ga₂O₃ with Nb₂O₅, and the decrease in the Abbe number was significantly suppressed when Ta₂O₅ was incorporated into the glass. As a result, excellent compatibility between high refractive index and lower wavelength dispersion was realized in La₂O₃–Ga₂O₃–Ta₂O₅ glasses. Analysis based on the single‐oscillator Drude–Voigt model provided more systematical information and revealed that this compatibility was due to an increase in the electron density of the glass.     

Y3Al5O12–SiO2 Glasses: Structure and Polyamorphism

Aerodynamic levitation and CO₂ laser melting have been used to synthesize the yttrium aluminosilicate glasses zY₂O₃–yAl₂O₃–xSiO₂ with z/y = 3/5 corresponding to the YAG (Y₃Al₅O₁₂) composition and x between ~5 and ~45 mol%. The low‐ and high‐density (LDA inclusion and HDA matrix) polyamorphic phases in glasses with less than ~14 mol% SiO₂ were identified with backscattering electron imaging. Polarized and depolarized Raman spectra show the formation of various Qⁿ SiO₄ species whose relative populations change smoothly as the SiO₂ content is altered. The AlOs (s = 4–6) and YOz (z = 6–9) polyhedra formed in the YAG glass are preserved upon silica additions while the terminal oxygens of the Q²AlO₄ tetrahedra are gradually bridged to the Qⁿ‐SiO₄ species. The low‐frequency Boson Peak overlaps with the vibrational spectrum and its maximum is redshifted with increasing silica content. Micro‐Raman spectra measured for the LDA and HDA amorphous phases are found to be similar to the spectra of the bulk glass indicating common structural characteristics. The stability of the LDA phase against crystallization appears to be lower than that of the HDA phase. The crystallinity on certain inclusions consisted of YAG microcrystals and a new unidentified microcrystalline phase within Y₄Al_2(1?x)Si_2xO_(9+x) solid solution.     

Controlled nano-crystallization of IR frequency-doubling Cd4GeS6 crystal in chalcogenide glass

Crystallization of IR frequency-doubling nanocrystals in chalcogenide glasses is a promising approach to achieve novel nonlinear optical materials. However, controllable glass crystallization remains challenging. In this study, IR-transparent chalcogenide glass-ceramics containing novel Cd₄GeS₆ IR frequency-doubling nanocrystals (about 60-80 nm) are fabricated through controlled nano-crystallization. Nanocrystalline structure of the Cd₄GeS₆ nano-crystallized glass-ceramics is investigated in detail through X-ray diffractometer, field emission scanning electron microscope, and Raman scattering techniques. The structural similarity of [Cd₄GeS₆] polyhedron in the network structure of as-prepared glass is found to be responsible for the nucleation of Cd₄GeS₆ crystal. A unique microstructure of Cd₄GeS₆ nanocrystals embedded GeS₂ phase-separated structure is discovered in samples thermally treated at high temperatures (370°C and 380°C). This study would not only shed more light on glass crystallization mechanism but also provide a feasible approach for the design and fabrication of new IR frequency-doubling materials through glass crystallization.