Radial IR-GRIN lens prepared by multi-temperature fields manipulated gradient crystallization within chalcogenide glass.

Chalcogenide glass has achieved great success in manufacturing axial-type infrared gradient refractive index (IR-GRIN) lenses. However, studies on radial-type IR-GRIN lenses, which are more ideal for optical design, remain rare. The present study introduces what we believe to be a new method for preparing radial IR-GRIN lens by creating high refractive index (n) In2S3 nanocrystals within a 65GeS2-25In2S3-10CsCl (GIC, in molar percentage) glass matrix. Upon introduction of multi-temperature field manipulation, we have successfully achieved central crystallization and simultaneous gradient attenuation spreading toward the edge within GIC glass, providing a radial GRIN profile with Δn over 0.1 while maintaining excellent IR transparency. In addition, the optical and structural properties of the GIC GRIN samples were characterized. The relationship between Raman intensity and the n of glass ceramics at different heat treatment temperatures was investigated, thereby enabling the indirect confirmation of the presence of radial gradient crystallization within the prepared GIC GRIN samples through Raman intensity. Multiple experimental results have shown that this approach has excellent reproducibility and potential for large-scale productions.

Broadband SnS/Te photodetector to long-wavelength infrared: breaking the spectrum limit through alloy engineering.

Materials based on group IV chalcogenides, are considered to be one of the most promising materials for high-performance, broadband photodetectors due to their wide bandgap coverage, intriguing chemical bonding and excellent physical properties. However, the reported photodetectors based on SnS are still worked at relatively narrow near-infrared band (as far as 1550 nm) hampered by the nonnegligible bandgap of 1.1-1.5 eV. Here, a novel photodetector based on Te alloyed SnS thin film was demonstrated with an ultra-broadband response up to 10.6 µm. By controlling the Te alloyed concentration in SnS increasing to 37.64%, the bandgap narrows to 0.23 eV, exhibiting a photoresponse potential at long-wavelength infrared excitation. Our results show Te-alloying can remarkably enhance the detection properties of SnS/Te photodetectors. The photoresponsivity and detectivity of 1.59 mA/W and 2.3 × 108 Jones were realized at 10.6 µm at room temperature. Moreover, the nonzero photogain was observed generated by nonlinearly increased photocurrent density, resulting in a superlinear dependency between photoresponsivity and light intensity. Our studies successfully broaden photoresponse spectrum of SnS toward the mid-infrared range for the first time. It also suggests that alloying is an effective technique for tuning the band edges of group IV chalcogenides, contributing deep implications for developing future optoelectronic applications.

Solution-processed Er3+-Doped GeS2 chalcogenide glass films with NIR photoluminescence towards functional flexibility and integration.

Rare-earth doped chalcogenide films are major components in flexible and integrated photonic and optoelectronic devices for modern communication systems, metrology, and optical sensing. However, it is still challenging to develop a high concentration of rare-earth doping chalcogenide film with a smooth surface to realize efficient photoluminescence (PL). Here, we demonstrate that Er3+-doped GeS2 films are prepared by spin-coating based on a two-step dissolution process. Such a two-step process provides the high solubility of Er3+ in GeS2 films and exhibits efficient emission at ∼1.5 µm crossing the telecommunication C-band. The highest PL emission intensity is obtained in GeS2 films doped with 1.4 mol% of Er3+, and this PL in GeS2 films is reported for the first time. We propose adjustments of annealing parameters for improving the PL characteristics in such materials. Through the control precision of the heating rate and annealing temperature, the smooth surface of GeS2 films enables efficient photo-luminescence. This two-step dissolution-based strategy would pave a new path to design luminescent chalcogenide films for application in flexible and integrated optoelectronics and photonics.

Optimization of multispectral chalcogenide glass for large-size fabrication.

Chalcogenide glass has become one of the essential IR lens materials in passively athermalized long-wave IR devices. However, that there is no multispectral chalcogenide glass capable of large-size fabrication raises challenges to the development and popularization of multispectral imaging systems combining visible, near-IR, and mid-IR. In this work, we developed a novel chalcogenide glass capable of a record-big (Ø120 mm) fabrication through the compositional optimization of GeS2-Ga2S3-CsCl glass with introduction of Sb2S3. Its transmission window is characterized as ranging from 0.51 to 11.2 µm, which means it could be employed as a multispectral lens transmitting visible and IR signals in a co-aperture IR optical system. In addition, a method of three-stage thermal analysis is proposed to evaluate the glass-forming ability of chalcogenide glass through simulating the melt-quenching process of chalcogenide melt in a vacuum-sealed silica ampoule. This work not only shows an innovative multispectral chalcogenide glass with promising applications but also introduces a simple and convenient technique for screening chalcogenide glass with ultrahigh glass-forming ability capable of large-size fabrication.

Third-order optical nonlinearity of CsPb(Br/I)3 metal halide perovskites nano-crystals embedded chalcogenide glass.

The nonlinear optical properties of emerging metal halide perovskites (MHP) materials are sufficiently intriguing that this topic has become the hotspots in the realm of material science. Hence, we investigate the third-order nonlinear optical properties of CsPbBrx/I3-x (x = 1, 2, 3) MHP nano-crystals (NCs) embedded chalcogenide glass (ChG) within a GeS2-Sb2S3 pseudo-binary system, by monitoring the composition, excitation wavelength and intensity dependencies via femtosecond Z-scan technique. We have found that the intrinsic large optical nonlinearity of ChG can be further enhanced because of the incorporation of MHP NCs, and that the optical nonlinearity of MHP-ChG containing pristine Br NCs is more pronounced compared to its counterparts with mixed Br/I NCs, due to a combination of multiple factors.

Tunable broadband near-infrared luminescence in glass realized by defect-engineering.

Tunable broadband near-infrared (NIR)-luminescent materials play a crucial role as light sources and tunable fiber lasers in modern technologies such as high-capacity telecommunication, imaging, and remote sensing. Despite considerable effort in studying the luminescent materials doped with rare-earth or transition metal ions, it is still challenging to achieve tunable broadband emission in photonic materials, especially in glasses, for active-fiber applications. In the present work, such NIR emission is achieved by modifying oxygen-deficient structural defects (i.e., singly ionized oxygen vacancies (VO∙) in tellurium (Te)-doped germanate glass). The local glass chemistry around Te is controlled by engineering singly ionized oxygen vacancies (VO∙) in alkali-alumino-germanate glass. This enables fine-tuning of the configurations and chemical states of Te centers over a wide range of chemical states, from ionic states to neutrally charged clusters and to positively charged clusters, resulting in various intriguing luminescent behaviors (e.g., wavelength-tunable emission, great emission enhancement, bandwidth extension).

Spectral fitting method for obtaining the refractive index and thickness of chalcogenide films.

Spectral fitting method (SFM) was proposed to obtain the refractive index (RI) and thickness of chalcogenide films based on transmission spectra. It extended the Swanepoel method to the films on the order of hundreds of nanometers in thickness. The RI and thickness of the films can be obtained quickly and accurately by using the SFM based on the transmission spectrum with only one peak and valley. The method's reliability theoretically was evaluated by simulation analysis. The results showed that the accuracy of the RI and thickness was better than 0.2% by using the SFM regardless of thin or thick film. Finally, the RI and thickness of the new ultralow loss reversible phase-change material Sb2Se3 films were obtained experimentally by the SFM. This work should provide a useful guideline for obtaining the RI and thickness of the transparent optical films.

Luminescent ion-doped transparent glass ceramics for mid-infrared light sources [invited].

Glass ceramics (GCs), which consist essentially of a homogeneous solid state dispersion of nanocrystals (NCs) embedded in a chemically inert and mechanically robust glass matrix, appear to be an extremely promising class of solid state materials that can be easily tailored into arbitrary shapes, including a new generation of optical fibers, for efficient incoherent and coherent sources of mid-infrared (MIR) light emission. This unique capability not only stems from the fact that one can tailor the underlying glass matrix for optimal macroscopic physical properties and ultrahigh transparency at the wavelengths of interest (resulting in appropriate "transparent glass ceramics" or TGCs), but also stems from the fact that one can embed these matrices with size and structure-tailored NCs, which in turn can be doped with relatively high concentrations of MIR emitting rare-earth or transition metal ions. This potential is tantamount to the localization of these highly efficient MIR ionic emitters into carefully selected and highly favorable "process-engineered" custom crystalline host "nanocages," while insulating the ionic emitters from the emission-quenching glass host matrix, the latter being chosen largely because of its highly favorable macroscopic bulk properties, including its ductility and formability into near-arbitrary shapes (at appropriate temperatures). Such MIR TGCs appear to be very promising for numerous photonics applications, including compact and relatively efficient waveguide sensors, broadband incoherent MIR light sources, superluminescent light sources, advanced fiber-optic devices, and broadly wavelength-tunable and ultrashort pulse mode-locked fiber and bulk solid-state lasers. In this paper, we review past achievements in this field, starting with an overview of TGCs, followed by discussions of currently preferred methods of fabrication, characterization, and optimization of suitably doped oxyfluoride, tellurite, and chalcogenide TGCs and of our projections of anticipated future developments in this field at both the materials and device levels.

Trapped excited electrons in Ni2+-doped perovskite KZnF3 nanocrystals in KF-ZnF2-SiO2 glass ceramics: publisher's note.

This publisher's note contains a correction to Opt. Lett.45, 4984 (2020)OPLEDP0146-959210.1364/OL.402229.

Trapped excited electrons in Ni2+-doped perovskite KZnF3 nanocrystals in KF-ZnF2-SiO2 glass ceramics.

The photonic properties of glass ceramics (GCs) are often enabled by encapsulating nanocrystals (NCs) and doped transition metal ions (TMIs). However, it is difficult to probe the optics-related effect between the host NCs' band structure and doped TMIs' d-d orbitals. Herein, perovskite-type KZnF3:NiNCs in KF-ZnF2-SiO2 GCs were prepared and taken as a model system. The excited-state dynamics of host NCs and Ni ions' d-d orbitals were studied by transient absorption spectroscopy. It presents a strong interaction between Ni's d orbitals and the band edge, which could extract excitonic energy in photonic applications. These findings facilitate understanding and design of TMIs-doped GCs in real-life photonic applications.

Extension of the Swanepoel method for obtaining the refractive index of chalcogenide thin films accurately at an arbitrary wavenumber.

The well-known Swanepoel method was often used to obtain the refractive index (RI) of thin films at the wavenumber values corresponding to the extremes of the transmission interference fringes. But it is difficult to accurately obtain the RI of chalcogenide thin films, especially at an arbitrary wavenumber. So a regional approach method (RAM) was presented here to extend the Swanepoel method to an arbitrary wavenumber. In the RAM the RI at the arbitrary wavenumber was determined through dynamic matching. The calculated values were used to match the experimental transmittance. The accuracy of the RI is better than 0.5%. The RI of a well-known film was obtained by the RAM. And the results are in great agreement with the true values of the RI of the film which indicates the correctness and effectiveness of the RAM. Moreover, the transmission spectrum of Ge-Sb-Se film was measured in the ultra-broadband range of 2000-18000 cm-1 (555-5000 nm), and finally the RI of the film was obtained at the 22 wavenumbers of the spacer 600 cm-1 by the RAM.

Improvement of Swanepoel method for deriving the thickness and the optical properties of chalcogenide thin films.

A tangencypoint method (TPM) is presented to derive the thickness and optical constants of chalcogenide thin films from their transmission spectra. It solves the problem of the abnormal value of thickness in the strong absorption region obtained by Swanepoel method. The accuracy of the thickness and refractive index is better than 0.5% by using this method. Moreover, comparing with Swanepoel method by using the same simulation and experimental data from the transmission spectrum, the accuracy of the thickness and refractive index obtained by the TPM is higher in the strong absorption region. Finally the dispersion and absorption coefficient of the chalcogenide films are obtained based on the experimental data of the transmission spectrum by using the TPM.

High Verdet constants and diamagnetic responses of GeS2-In2S3-PbI2 chalcogenide glasses for integrated optics applications.

Chalcogenide glasses as kind of diamagnetic magneto-optical materials have promising applications in the field of integrated optics and optical communication systems due to their excellent properties, such as easy to be processed into waveguide and temperature independence of the Verdet constants. For clarifying the influence factors following the compositional variation on Faraday effect and finding a glass with a large Verdet constant, novel pseudo-ternary chalcogenide glass system, GeS2 - In2S3 - PbI2, was prepared and investigated. The composition, wavelength and temperature dependences on the Verdet constants were systematically investigated at the wavelengths of 635, 808, 980 and 1319 nm. PbI2 was confirmed to have positive contribution to the Verdet constant and the Becquerel rule was proved to be an effective guidance for predicting the Verdet constant in chalcogenide glasses. The 60GeS2·15In2S3·25PbI2 glass was found to possess the largest Verdet constant (V = 0.215 min·G-1·cm-1, @808nm), which is great larger than that of commercial diamagnetic glasses. These glasses also possess good glass-forming ability and VIS-IR transmittance, therefore be a good candidate for next-generation integrated optical isolator and other magneto-optical devices.

Nanocrystallization in Oxyfluoride Glasses Controlled by Amorphous Phase Separation.

Transparent bulk glass-ceramics containing ZnF2, K2SiF6, and KZnF3 nanocrystals are successfully obtained from xKF-xZnF2-(100 - 2x)SiO2 oxyfluoride glasses for the first time to the best of our knowledge. The glass transition temperatures of heat-treated samples increase with time and approach values that resemble the temperatures chosen for thermal treatment. During nucleation and crystal growth, the residual glass around the crystals is depleted in fluoride which as glass component usually leads to a decrease in viscosity. The crystallization behavior notably depends on the glass composition and changes within a small range from x = 20 to 22.5 mol %. The occurrence of liquid/liquid phase separation in dependence of the composition is responsible for the physicochemical changes. Two different microstructures of droplet and interpenetrating phase separation and their compositional evolution are observed by replica transmission electron microscopy technique in the multicomponent glassy system. This study suggests that the size and crystal phase of precipitated crystallites can be controlled by the initial phase separation.

Broadband near-IR emission from cubic perovskite KZnF(3):Ni(2+) nanocrystals embedded glass-ceramics.

Transparent KF-ZnF(2)-SiO(2) glass-ceramics were prepared with the precipitation of KZnF(3)Ni(2+) nanocrystals. During excitation with a wavelength of 405 nm at room temperature, a broadband near-IR emission centered at 1695 nm with the FWHM of more than 350 nm was observed, which is originated from the T(2g)3(F3)→A(2g)3(F3) transition of octahedral Ni(2+) incorporated in the KZnF(3) crystalline phase. In comparison to oxide glass-ceramics, a redshift of the luminescence is observed, which is due to the low crystal field of these octahedral Ni(2+). The shift and extension of near-IR emission in the KZnF(3):Ni(2+) nanocrystals embedded in a glassy matrix do not only complete the broadband emission in the whole near-IR region for the Ni(2+) ions-based photonics, but also open an easy way to approach the broadband optical amplifier and tunable lasers operating in the wavelength region near 1800 nm, which was up to now achieved by codoping of several types of active ions.

Quantum cutting in Pr3+-Yb3+ codoped chalcohalide glasses for high-efficiency c-Si solar cells.

Downconversion materials, which can convert one high-energy photon to two low-energy photons, have provided a promising avenue for the enhancement of solar cell efficiency. In this work, the Pr3+-Yb3+ codoped 25GeS2-35Ga2S3-40CsCl chalcohalide glasses were synthesized in a vacuumed silica ampoule by the melting-quenching technique. Under 474 nm excitation, the visible and near-IR emission spectra reveal the energy transfer from Pr3+ to Yb3+ ions, resulting in the intense 1008 nm near-IR emission for the c-Si solar cells. By tuning the excitation laser power, it is determined that one visible photon has been cut into two near-IR photons during the energy transfer process. With the help of an integrated sphere, the real quantum yields of near-IR emissions were calculated. For the 0.2Pr2S3-0.2Yb2S3 (in mol.%) codoped chalcohalide glass, the quantum yield equals 10.8%. Although this efficiency is still low, this result will open a new route to realize the efficient spectral modification of the solar spectrum.

Ultraflexible Temperature-Strain Dual-Sensor Based on Chalcogenide Glass-Polymer Film for Human-Machine Interaction.

Skin-like thermoelectric (TE) films with temperature- and strain-sensing functions are highly desirable for human-machine interaction systems and wearable devices. However, current TE films still face challenges in achieving high flexibility and excellent sensing performance simultaneously. Herein, for the first time, a facile roll-to-roll strategy is proposed to fabricate an ultraflexible chalcogenide glass-polytetrafluoroethylene composite film with superior temperature- and strain-sensing performance. The unique reticular network of the composite film endows it with efficient Seebeck effect and flexibility, leading to a high Seebeck coefficient (731 µV/K), rapid temperature response (≈0.7 s), and excellent strain sensitivity (gauge factor = 836). Based on this high-performance composite film, an intelligent robotic hand for action feedback and temperature alarm is fabricated, demonstrating its great potential in human-machine interaction. Such TE film fabrication strategy not only brings new inspiration for wearable inorganic TE devices, but also sets the stage for a wide implementation of multifunctional human-machine interaction systems.

Performance improvement of transparent germanium-gallium-sulfur glass ceramic by gold doping for third-order optical nonlinearities.

Transparent chalcogenide glass ceramics were prepared by thermally treating gold-doped germanium-gallium-sulfur glass. The gold, as nucleating agents, modified the crystallization process of the glass, resulting in the formation of nanocrystals belonging to a single α-Ga2S3 phase. The crystalline grains increased in number with the treatment duration while their size remained constant, leading to a high infrared transmittance of the glass ceramics. Z-scan measurements revealed the performance improvement of the α-Ga2S3 nanocrystals to third-order optical nonlinearities.

High Seebeck Coefficient Inorganic Ge15Ga10Te75 Core/Polymer Cladding Fibers for Respiration and Body Temperature Monitoring.

Wearable thermal sensors based on thermoelectric (TE) materials with high sensitivity and temperature resolution are extensively used in medical diagnosis, human-machine interfaces, and advanced artificial intelligence. However, their development is greatly limited by the lack of materials with both a high Seebeck coefficient and superior anticrystallization ability. Here, a new inorganic amorphous TE material, Ge15Ga10Te75, with a high Seebeck coefficient of 1109 µV/K is reported. Owing to the large difference between the glass-transition temperature and initial crystallization temperature, Ge15Ga10Te75 strongly inhibits crystallization during fiber fabrication by thermally codrawing a precast rod comprising a Ge15Ga10Te75 core and PP polymer cladding. The temperature difference can be effectively transduced into electrical signals to achieve TE fiber thermal sensing with an accurate temperature resolution of 0.03 K and a fast response time of 4 s. It is important to note that after the 1.5 and 5.5 K temperatures changed repeatedly, the TE properties of the fiber demonstrated high stability. Based on the Seebeck effect and superior flexibility of the fibers, they can be integrated into a mask and wearable fabric for human respiration and body temperature monitoring. The superior thermal sensing performance of the TE fibers together with their natural flexibility and scalable fabrication endow them with promising applications in health-monitoring and intelligent medical systems.

Halogen Doping Mechanism and Interface Strengthening in the Na3SbS4 Electrolyte via Solid-State Synthesis.

Good-performing sodium solid electrolytes (SSEs) are essential for constructing all-solid-state sodium-ion batteries operating at ambient temperature. Sulfide solid electrolyte, Na3SbS4 (NBS), an excellent SSE with good chemical stability in humid air, can be synthesized with low-cost processing. However, Na3SbS4-based electrolytes with liquid-phase synthesis exhibit conductivities below milli-Siemens per centimeter. Thus, a series of halogen-doped samples formulated as Na3-xSbS4-xMx (0 ≤ x ≤ 0.3, M = Cl, Br, and I) were experimentally prepared in this study using the solid-state method to improve the battery performance. X-ray diffraction with refinement analysis and Raman spectroscopy were employed to understand deeply the connection between the crystal structure and conductivity of Na+ ions. In addition, symmetric sodium batteries with Na2.85SbS3.85Br0.15 were tested at room temperature, and pristine Na3SbS4 was used as the control group. The result showed that the symmetric sodium battery assembled with the Na2.85SbS3.85Br0.15 electrolyte can stably cycle for longer than 100 h at a current density of 0.1 mA/cm2. This research provides a method to manufacture novel SSEs by elaborating the effect of halogen doping in NBS.