Effect of Se on Structure and Electrical Properties of Ge-As-Te Glass

Chalcogenide GRIN glasses with high refractive index and large refractive index difference for LWIR imaging

Gradient refractive index (GRIN) materials utilize an internally tailored refractive index in combination with the designed curvature of the optical element surface, providing the optical designer with additional freedom for correcting chromatic and spherical aberrations. In this paper, new GRIN materials suitable for the second (3-5 µm) and third (8-12 µm) atmospheric windows were successfully developed by the thermal diffusion method based on Ge20As20Se60-xTex series high refractive index glasses, where the maximum refractive index difference (Δn) at 4 µm and 10.6 µm were 0.281 and 0.277, respectively. The diffusion characteristics and refractive index distribution of the GRIN glass were analyzed by Raman characterization. Furthermore, the performance of GRIN singlet and homogeneous singlet in the LWIR band (8 µm, 10.6 µm (primary wavelength), 12 µm) was compared, and the results showed that the GRIN singlet had better chromatic aberration correction and unique dispersion characteristics.

Infrared Evanescent Wave Sensing Based on a Ge10As30Se40Te20 Fiber for Alcohol Detection

Infrared evanescent wave sensing based on chalcogenide fiber is an emerging technology for qualitative and quantitative analysis of most organic compounds. Here, a tapered fiber sensor made from Ge₁₀As₃₀Se₄₀Te₂₀ glass fiber was reported. The fundamental modes and intensity of evanescent waves in fibers with different diameters were simulated with COMSOL. The 30 mm length tapered fiber sensors with different waist diameters, 110, 63, and 31 μm, were fabricated for ethanol detection. The sensor with a waist diameter of 31 μm has the highest sensitivity of 0.73 a.u./% and a limit of detection (LoD) of 0.195 vol.% for ethanol. Finally, this sensor has been used to analyze alcohols, including Chinese baijiu (Chinese distilled spirits), red wine, Shaoxing wine (Chinese rice wine), Rio cocktail, and Tsingtao beer. It is shown that the ethanol concentration is consistent with the nominal alcoholicity. Moreover, other components such as CO₂ and maltose can be detected in Tsingtao beer, demonstrating the feasibility of its application in detecting food additives.

High Refractive Index GRIN Lens for IR Optics

Infrared gradient refractive index (GRIN) material lenses have attracted much attention due to their continuously varying refractive index as a function of spatial coordinates in the medium. Herein, a glass accumulation thermal diffusion method was used to fabricate a high refractive index GRIN lens. Six Ge_17.2As_17.2Se_xTe_(65-x) (x = 10.5-16) glasses with good thermal stability and high refractive index (n_{@10 μm} > 3.1) were selected for thermal diffusion. The refractive index span (∆n) of 0.12 was achieved in this GRIN lens. After thermal diffusion, the lens still had good transmittance (45%) in the range of 8-12 μm. Thermal imaging confirmed that this lens can be molded into the designed shape. The refractive index profile was indirectly characterized by the structure and composition changes. The structure and composition variation became linear with the increase in temperature from 260 °C to 270 °C for 12 h, indicating that the refractive index changed linearly along the axis. The GRIN lens with a high refractive index could find applications in infrared optical systems and infrared lenses for thermal imaging.

SbI3·3S8: A Novel Promising Inorganic Adducts Crystal for Second Harmonic Generation

In the past twenty years, the basic investigation of innovative Non-Linear Optical (NLO) crystals has received significant attention, which has built the crucial heritage for the use of NLO materials. Fundamental research is essential given the scarcity of materials for NLO compounds, especially in the deep ultraviolet (DUV) and middle- and far-infrared (MFIR) regions. In the present work, we synthesized high-quality MFIR SbI₃·3S₈ NLO crystals having a length in the range of 1-5 mm through rapid facile liquid phase ultrasonic reaction followed by the assistance of instantaneous natural evaporation phenomenon of the solvent at room temperature. X-ray diffraction (XRD) results ratify the hexagonal R3m structure of SbI₃·3S₈ crystal, and energy-dispersive X-ray spectroscopy (EDX) demonstrates that the elemental composition of SbI₃·3S₈ crystal is similar to that of its theoretical composition. The direct and indirect forbidden energy gaps of SbI₃·3S₈ were measured from the optical transmittance spectra and they were shown to be 2.893 eV and 1.986 eV, respectively. The green sparkling signal has been observed from the crystal during the second harmonic generation (SHG) experiment. Therefore, as inorganic adducts are often explored as NLO crystals, this work on the MFIR SbI₃·3S₈ NLO crystal can bring about additional investigations on this hot topic in the near future.

Structure-property relationships in critically connected (GeTe4)100-x(As2Se3)x glasses

Thermal, optical, mechanical and structural studies were carried out on glasses in the pseudo-binary joint GeTe₄-As₂Se₃ prepared by a melt quenching method. (GeTe₄)_100-x(As₂Se₃)_x glasses in the entire composition range of 0 ≤ x ≤ 100 have an average coordination number (Z_av) = 2.4, where the glass forming ability is found to be maximum. In general, for Z_av ≤ 2.4, the glass transition is found to be dominated by the network connectivity and the chemical composition effects are minimal. Although Z_av of Ge₂₀Te₈₀ (GeTe₄) and As₂Se₃ (As₄₀Se₆₀) is 2.4, GeTe₄ is a poor glass former and As₂Se₃ is an excellent glass former. The glass-forming ability is expected to increase with the addition of As₂Se₃. Surprisingly, the glass forming ability is found to decrease with the initial addition of As₂Se₃ and then shows an increasing trend. Glass transition (T_g) shows a large variation from 175 °C for x = 0 to 108 °C for x = 30. Based on the variation in the properties, the tie-line can be divided into three regions: region I (0 ≤ x ≤ 20) where T_g shows a decreasing trend, region II (25 ≤ x ≤ 55) where T_g remains almost constant and region III (60 ≤ x ≤ 100) where T_g shows an increasing trend. Hardness measurement also shows a similar trend in the three regions. Thermal stability shows a continuous increase with the increase of As₂Se₃. The fragility index varies between 15 and 30 for all these glasses except for x = 0 (GeTe₄) indicating the strong nature of the melts containing As₂Se₃. Raman studies indicate that the glassy network is dominated mainly by GeTe_(4/2) in region I and in region III the network is dominated by AsSe_(3/2) based structures. Glasses in region II are found to be dominated by AsTe_3/2 based structures. This study brings out the dominance of chemical composition effects over the network connectivity in a critically coordinated network. These glasses are also found to transmit IR light up to 18 μm and offer a wide composition range to prepare bulk glasses to be useful for infrared applications.