Correlating Structure with Threshold Behavior of Chalcogenide Glasses Within Ge–Sn–Se Ternary System

A systematic investigation of the optical and structural properties of chalcogenide glasses in Ge–Sn–Se ternary system is presented. We have found a threshold behavior of optical property, namely, existence of transitional composition of the Ge–Sn–Se glasses, with progressive replacement of Se by Sn. Calculation of mean coordination number indicates that the transition‐like feature of optical property is associated with the evolution of chemical ordering of the Ge–Sn–Se network. Analysis of Raman spectra of the glasses explains that the interaction between Se–Se bonds, Sn(Se_1/2)₄ tetrahedra, and Sn–Sn homopolar bonds is the origination of such optical phenomenon.     

Structure and physical properties of Ge15Sb20Se65‐xSx glasses

We explored the structure and physical properties of Ge₁₅Sb₂₀Se_65‐xS_x (with x = 0, 16.25, 32.5, 48.75, and 65) glasses in order to screen the best compositions for the applications in photonics, since the laser damage thresholds in Se‐based glasses are too low although their optical nonlinearities are high. We found that, linear and nonlinear refractive index of the glasses decreased, but glass transition temperature T_g, optical bandgap E_g and the laser damage threshold increased with increasing S content. We further employed Raman scattering and high‐resolution X‐ray photoelectron spectra to probe the structure of the glasses. Through the analysis of the evolution of the different structural units in the glasses, it was concluded that, the heteropolar bonds (Ge–Se/S, Sb–Se/S) were dominated in these glasses. With the increase in chalcogen Se/S ratio, the number of the Se‐related chemical bonds (Ge–Se, Sb–Se and Se–Se) increased and that of S‐related chemical bond (Ge–S, Sb–S and S–S) decreased gradually, and Ge was prior to bond with S rather than Se. The elemental substitution thus had negligible effect on the glass structure. The change of the physical properties was mainly due to the difference of the strength of the chemical bonds between S–Ge(Sb) and Se–Ge(Sb).     

Compositional dependence of crystallization in Ge–Sb–Se glasses relevant to optical fiber making

For fiber‐optic mid‐infrared bio‐ and chemical‐sensing, Ge–Sb–Se glass optical fibers are more attractive than Ge–As–Se because of: (i) lowered toxicity and (ii) lower phonon energy and hence transmission to longer wavelengths, with potential to reach the spectral “fingerprint region” for molecular sensing. There is little previous work on Ge–Sb–Se fibers. Here, fibers are fabricated from two glass compositions in the Ge_xSb₁₀Se_90?x atomic (at.) % series. Both glass compositions are of similar mean‐coordination‐number, lying in the overconstrained region, yet of different chemical composition: stoichiometric Ge₂₅Sb₁₀Se₆₅ at. % and non‐stoichiometric Ge₂₀Sb₁₀Se₇₀ at. %. Thermal analysis on bulk glasses has previously shown that the former exhibited the maximum glass stability of the series. However, during fiber‐drawing of Ge₂₅Sb₁₀Se₆₅ at. %, the preform tip is found to undergo surface‐devitrification to monoclinic GeSe₂ alone, the primary phase, no matter if the preform is an annealed, as‐melted rod or annealed, extruded rod. The heating rate of the preform‐tip to the fiber‐drawing temperature is estimated to be up to ~100°C/min to ~490°C. Lower heating rates of 10°C/min using thermal analysis, in contrast, encourage crystallization of both Sb₂Se₃ and GeSe₂. The non‐stoichiometric: Ge₂₀Sb₁₀Se₇₀ at. % composition drew successfully to low optical loss fiber, no matter whether the preform was an annealed, as‐melted rod or annealed, extruded rod.     

Optical Amplification at 1.3 μm in a Praseodymium-Doped Sulfide-Glass Fiber

Praseodymium-doped glasses were prepared in the Ga-Na-S (GNS) system and their optical properties were studied. A single-mode fiber with an attenuation loss of 1.2 dB/m at a wavelength of 1.31 μm was fabricated using an extrusion method, and the amplification characteristics were measured in the bidirectional pumping configuration. We demonstrated a gain coefficient of 0.81 dB/mW at a wavelength of 1.34 μm, which is the highest we have ever reported, and achieved a net gain of 32 dB for a pump power of 90 mW. Highly efficient optical amplification at a wavelength of 1.3 μm was demonstrated in the praseodymium-doped GNS fiber.     

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.     

Magneto‐optical effects of Ge‐Ga‐Sb(In)‐S chalcogenide glasses with diamagnetic responses

The Faraday effects of Ge‐Ga‐Sb(In)‐S serial chalcogenide glasses were investigated at the wavelengths of 635, 808, 980, and 1319 nm, respectively. The compositional dependences were analyzed and associated influencing factors including the absorption edge, the concentration of Sb³⁺/In³⁺ ions, and the wavelength dispersion of refraction index were discussed. 80GeS₂·20Sb₂S₃ composition glass was found to have the largest Verdet constant (V=0.253, 0.219, 0.149, and 0.065 min·G^?1·cm^?1 for wavelengths 635, 808, 980, and 1319 nm, respectively) in these glasses, which is larger than that of commercial diamagnetic glasses (Schott, SF 6, V=0.069 min·G^?1·cm^?1@633 nm, for example). Sb³⁺ ions with high polarizability possessing s²‐sp electron jumps involving ¹S₀→¹P₁, ³P_0,1,2 transitions are responsible for large Verdet constant, and Becquerel rule is proved to be an effective guidance for estimating the Verdet constant and further optimizing the compositions in chalcogenide glasses.     

Nonlinear negative transmittance at a CW 980‐nm laser diodes pumping in Yb3+:CaF2 nanocrystals‐embedded glass ceramics

Cooperative upconversion luminescence (CUCL) occurs in spectral regions in which single ions do not have energy levels. However, all results reported so far are concentrated on luminescence properties from Yb³⁺ ions‐doped various hosts. Here, we report the observation of nonlinear negative transmittance (NNT) at continuous‐wavelength (CW) 980‐nm laser diodes (LDs) pumping in silicate oxyfluoride glass ceramics (GCs)‐containing CaF₂:Yb³⁺ nanocrystals. The unique optical nonlinearity is analyzed based on energy‐level transitions, dynamic evolution, rate equation, and power transmission equation, which can be explained as the cooperative optical absorption for the intense CUCL of Yb³⁺ ions. The NNT in the CaF₂:Yb³⁺ nanocrystals‐embedded GCs can be tailored with the power of a CW 980‐nm LDs, which possesses potential for the development of future optical limiters and switches.     

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.     

On the coupled ferroelectric‐electrochromic effect of ε‐WO3

A reversible electrochromic effect has been observed for the first time in flame spray pyrolysis (FSP) processed ε‐WO₃ thin films without the use of an ion storage layer and an electrolytic layer. The dark coloration that appears upon the application of a voltage in films deposited on top of interdigitated gold electrodes is localized to the low voltage (?) electrode arm and it switches to the opposite arm upon a reversal of the polarity. Raman spectroscopy indicated that the coloration was not due to intercalation. It is argued here that the coloration is driven by the asymmetric ferroelectric properties of the ε‐WO₃ crystals and that this electrochromic reversibility is intrinsically coupled with the polarization switching of the device.     

Spectral management and energy‐transfer mechanism of Eu3+‐doped β‐NaGdF4:Yb3+,Er3+ microcrystals

β‐NaGdF₄:Yb³⁺,Er³⁺ upconversion (UC) microcrystals were prepared by a facile hydrothermal process with the assistance of ethylene diamine tertraacetic acid (EDTA). The β‐NaGdF₄ UC microcrystal morphology was controlled by changing the doses of EDTA and NaF. Uniform hexagonal structure can be obtained at the 2 mmol EDTA and 9‐10 mmol NaF. The UC emissions of β‐NaGdF₄:Yb³⁺,Er³⁺ microcrystals were tuned by the variation of Eu³⁺ doping level (0%‐5%), where the red/green intensity ratio decreased with the Eu³⁺ concentration increase. It was found on the base of rate equations that with the Eu³⁺ doping, the energy back transfer process ²H_11/2/⁴S_3/2 (Er³⁺) → ⁴I_13/2 (Er³⁺) decreased. In addition, an energy‐transfer process from ⁴F_7/2 (Er³⁺) to ⁵D₁ (Eu³⁺) and a cross relaxation process of ⁷H_9/2 (Er³⁺) + ⁵D₀ (Eu³⁺) → ⁴F_7/2 (Er³⁺) + ⁵D₂ (Eu³⁺) were proposed and verified by rate equations, which dominated the energy‐transfer mechanism between Er³⁺ and Eu³⁺, resulted in the spectra tuning of β‐NaGdF₄:Yb³⁺,Er³⁺. The results suggested that the color tuning of β‐NaGdF₄:Yb³⁺,Er³⁺,Eu³⁺ UC microcrystals would have potential applications in such fields as flat‐panel displays, solid‐state lasers, and photovoltaics.     

Synthesis of Eu3+‐doped BaBi2Ta2O9 based glass‐ceramic nanocomposites: Optical and dielectric properties

In this paper we report for the first time synthesis of Eu³⁺‐doped transparent glass‐ceramics (TGC) with BaBi₂Ta₂O₉ (BBT) as the major crystal phase using the glass system SiO₂–K₂O–BaO–Bi₂O₃–Ta₂O₅ by melt quenching technique followed by controlled crystallization through ceramming heat treatment. DSC studies were conducted in order to determine a novel heat‐treatment protocol to attain transparent GCs by controlling crystal growth. The structural properties of the BBT GCs have been investigated using XRD, FE‐SEM, TEM and FTIR reflectance spectroscopy. Optical band gap energies of the glass‐ceramic samples were found to decrease with respect to the precursor glass. An increased intensity of emission along with increase in the average lifetime of Eu³⁺ was observed due to incorporation of Eu³⁺ ions into the low‐phonon energy BBT crystal site. The local field asymmetric ratios of all the samples were observed greater than unity. The dielectric constant (ε_r), dielectric loss, and dissipation factor values of both the base glass and ceramized samples were found to decrease with increase in frequency.     

Remarkable piezoelectricity and stable high‐temperature dielectric properties of quenched BiFeO3–BaTiO3 ceramics

Effects of quenching process on dielectric, ferroelectric, and piezoelectric properties of 0.71BiFeO₃?0.29BaTiO₃ ceramics with Mn modification (BF–BT?xmol%Mn) were investigated. The dielectric, ferroelectric, and piezoelectric properties of BF–BT?xmol%Mn were improved by quenching, especially to the BF–BT?0.3 mol%Mn ceramics. The dielectric loss tanδ of quenched BF–BT?0.3 mol%Mn ceramics was only 0.28 at 500°C, which was half of the slow cooling one. Meanwhile, the remnant polarization P_r of quenched BF–BT?0.3 mol%Mn ceramics increased to 21 μC/cm². It was notable that the piezoelectric constant d₃₃ of quenched BF–BT?0.3 mol%Mn ceramics reached up to 191 pC/N, while the T_C was 530°C, showing excellent compatible properties. The BF–BT?xmol%Mn system ceramics showed to obey the Rayleigh law within suitable field regions. The Rayleigh law results indicated that the extrinsic contributions to the dielectric and piezoelectric responses of quenched BF–BT?xmol%Mn ceramics were larger than the unquenched ceramics. These results presented that the quenched BF–BT?xmol%Mn ceramics were promising candidates for high‐temperature piezoelectric devices.     

Structure‐property relationships in BiScO3–PbTiO3–PbMg1/3Nb2/3O3 ceramics near the morphotropic phase boundary

The phase structure, dielectric, ferroelectric, and piezoelectric properties of (1?2x)BiScO₃–xPbTiO₃–xPbMg_1/3Nb_2/3O₃ ceramics (x = 0.30‐0.46) were studied. It was found that an increase in x leads to a structural phase transition between the rhombohedral and tetragonal phase via an intermediate monoclinic phase and to a crossover from the nonergodic relaxor state to the ferroelectric one. It was proposed that at x > 0.42 the phase transition changes from second to first order. The assumption about the existence of a tricritical point on the phase diagram at x ≈ 0.42 with the enhanced dielectric response has been made. The observed structure‐property relationships of the studied solid solutions are discussed. It is shown that the solid solutions with x = 0.42 are characterized by the high piezoelectric parameters (d₃₃ = 509 pC/N, d₃₁ = ?178 pC/N, d_h = 153 pC/N), which makes possible their applications in sonar equipment.     

Effect of Microwave Processing on the Crystallization and Energy Density of BaO‐Na2O‐Nb2O5‐SiO2‐B2O3 Glass‐Ceramics

Barium sodium niobate (BNN) glass‐ceramics were successfully synthesized through a controlled crystallization method, using both a conventional and a microwave hybrid heating process. The dielectric properties of glass‐ceramics devitrified at different temperatures and conditions were measured. It was found that the dielectric constant increased with higher crystallization temperature, from 750°C to 1000°C, and that growth of the crystalline phase above 900°C was essential to enhancing the relative permittivity and overall energy storage properties of the material. The highest energy storage was found for materials crystallized conventionally at 1000°C with a discharge energy density of 0.13 J/cm³ at a maximum field of 100 kV/cm. Rapid microwave heating was found to not give significant enhancement in dielectric properties, and coarsening of the ferroelectric crystals was found to be critical for higher energy storage.     

Instant precipitation of KMgF3:Ni2+ nanocrystals with broad emission (1.3‐2.2 μm) for potential combustion gas sensors

Optical gas sensors present fundamental and industrial importance considering their broad applications. Challenges remain to obtain new photonic materials with broadband emission covering the absorption spectrum of typical combustion gases. Here, broadband near‐infrared (NIR) photoluminescence (PL) spanning the wide absorption spectrum of typical combustion products is realized through instant precipitation of stable cubic perovskite KMgF₃:Ni²⁺ nanocrystals inside an aluminosilicate glass matrix after melt‐quenching. Excited by an 808 nm laser diode, NIR luminescence with a peak centered at ~1624 nm and a bandwidth (FWHM) greater than 315 nm is observed, originating from ³T_2g(³F) → ³A_2g(³F) electronic transition of octahedral coordinated Ni²⁺ in KMgF₃ GC. Controlled precipitation of these perovskite crystals from a supercooled aluminosilicate melt enables immediate encapsulation and, hence, stabilization in an inorganic glass phase. While the precipitation temperature has only a small effect on crystallite size, it controls the redox state of the melt and the degree of dopant incorporation into the crystalline phase so that PL performance can be optimized. Spontaneous crystallization of perovskite nanocrystals inside glass may offer a new way to stabilize these novel nanocrystals. Moreover, spontaneous crystallization can be attractive in the control of activator partitioning and in the fabrication of composite fiber devices with high transparency and emission gain. In the present case, this offers a potential platform for broadly tunable gain media, for example, for combustion gas sensing.     

Preparation and photoluminescence properties with the site‐selected excitations of Bi3+‐activated Ba3Sc4O9 phosphors

A series of novel Bi³⁺‐doped Ba₃Sc₄O₉ phosphors were synthesized through the solid‐state reaction. Their photoluminescence, decay curves, and thermal quenching properties were investigated in detail. The Ba₃Sc₄O₉:Bi³⁺ phosphors could be efficiently excited in the ultraviolet and near‐ultraviolet region (300‐400 nm), and the photoluminescence properties possess an obvious site‐selected excitations phenomenon. When excited at the ultraviolet light (320‐360 nm), the phosphors present a green or a bluish green emission, and when excited at the near‐ultraviolet light (370‐390 nm), the phosphors always show a yellow emission. The emission spectra excited at the different wavelength can be decomposed into four components, which accord with the four cationic sites in the structure of Ba₃Sc₄O₉. The influence of the Bi³⁺ concentration on the photoluminescence properties is also investigated. Upon excitation at 330 and 377 nm, the Ba₃Sc₄O₉:Bi³⁺ both have good thermal quenching properties; their emission intensity of the peak at 150°C both exceed 60% of the initial value. The above results indicate that the Ba₃Sc₄O₉:Bi³⁺ phosphor is a promising candidate to provide green or yellow components for UV or near‐UV LEDs.     

Self‐limited crystallization‐mediated removal of hydroxyl in glass

The effective removal of hydroxyl groups (OH) is receiving the attention of scientists interested in developing high‐performance photonic glass. Previous approaches rely on stringent control of the various drying techniques which meet with limited success in silicate glass obtained by the sol‐gel method. Here, we present a novel in situ strategy to remove structural OH groups, based on the self‐limited nanocrystallization‐triggered local chemical reaction between OH and F^? in the glassy phase. The experimental data revealed that a more than 100‐fold increase in the emission intensity can be realized. Moreover, the mechanism was discussed and it can be attributed to the effective removal of structural OH with especially strong binding energy. The results suggest an innovative avenue for the development of photonic glasses with efficient luminescence, excellent optical transmission, and improved reliability.     

High permittivity (1−x)Bi1/2Na1/2TiO3‐xPbMg1/3Nb2/3O3 ceramics for high‐temperature‐stable capacitors

(1?x)Bi_1/2Na_1/2TiO₃‐xPbMg_1/3Nb_2/3O₃[(1?x)BNT‐xPMN] ceramics have been fabricated via a conventional solid‐state method for compositions x ≤ 0.3. The microstructure, phase structure, ferroelectric, and dielectric properties of ceramics were systematically studied as high‐temperature capacitor materials. XRD pattern certified perovskite phase with no secondary phase in all compositions. As PMN concentration increased, the phase of (1?x)BNT‐xPMN ceramics transformed from ferroelectric to relaxor gradually at room temperature, with prominent enhancement of dielectric temperature stability. For the composition x = 0.2, the temperature coefficient of capacitance (TCC) was <15% in a wide temperature range from 56 to 350°C with high relative permittivity (>3300) and low dielectric loss (<0.02) at 150°C, which indicated promising future for (1?x)BNT‐xPMN system as high‐temperature stable capacitor materials.     

Development of optical grade (TbxY1−x)3Al5O12 ceramics as Faraday rotator material

Super full dense (Tb_xY_1?x)₃Al₅O₁₂ (x=0.5‐1.0) ceramics with optical grade (pore‐free) were successfully produced by solid‐state reaction between Tb₄O₇ and Al₂O₃ raw powders. Transparent sintered bodies were obtained by sintering at 1720°C for 5 hours in vacuum furnace. By additional HIP treatment, optical scattering centers were effectively removed, and finally the optical quality of the sintered bodies was improved to optical grade. Optical loss of the obtained samples at 1064 nm was approximately 0.1%/cm, and optically inhomogeneous parts were not observed inside the materials. Gaussian mode laser beam quality was not deteriorated after passing through the sample. Transmitted wavefront distortion inspected by interferometry was as excellent as λ/12. Verdet constant increased with an increase of Tb content in the garnet composition. When x=1.0, the Verdet constant was 307, 196, and 60 rad T^?1 m^?1 for 532, 633, and 1064 nm, respectively, at each measuring wavelength. These values were about 1.5 times higher than that of the commercially available TGG (Tb₃Ga₃O₁₂) crystal. Insertion loss of the produced (Tb_0.6Y_0.4)₃Al₅O₁₂ and TAG ceramics at 1064 nm was 0.01 and 0.05 dB, respectively, and extinction ratio was 39.5 and 40.3 dB, respectively. These properties were superior to that of the commercial high‐quality TGG single crystal (insertion loss: 0.05 dB, extinction ratio: 35.0 dB).     

Electro‐Optic Property of Mg2+/Er3+‐Codoped LiNbO3 Crystal: Mg2+ Concentration Threshold Effect

A series of Mg²⁺/Er³⁺‐codoped congruent LiNbO₃ crystals were grown by Czochralski method from the growth melts containing 0.5 mol% Er₂O₃ while varied MgO content from 0.0 to 7.0 mol%. The unclamped electro‐optic coefficients γ₁₃ and γ₃₃ of these crystals were measured by Mach–Zehnder interferometry. Two different voltage‐applying schemes were adopted: one is the DC voltage applied to the crystal via Al films coated onto crystal surfaces and another is via a pair of external Cu slab electrodes. The coefficients measured by the two schemes show similar strong dependence on Mg²⁺ concentration. The dependence is non‐monotonous, dramatic, and unusual, and reveals the features of two Mg²⁺ concentration thresholds of optical damage: one in the Mg²⁺ concentration range of 1.2–2.0 mol% (in crystal) and another in 4.5–5.0 mol%. Around the threshold the electro‐optic coefficient decreases abruptly at first and then recovers quickly, and the coefficient drops by >20% (12%) at the first (second) threshold, which exceeds the error 3% considerably. The dramatic behavior is qualitatively explained on the basis of the EO coefficient model of LiNbO₃ and the defect structure model for Mg²⁺‐doped LiNbO₃.