Tellurium Based Glasses For Mid- And Far- Infrared Sensing And Thermoelectric Applications

The tellurium-based glasses are of interest because of their transparency in the mid-and far-infrared range. Tellurium-based glasses and optical fibers can be used for the study of the atmosphere of terrestrial planets in Darwin project and the identification of chemical species in the daily life. Meanwhile, tellurium-based glasses, due to the intrinsic poor thermal conductivity and high Seebeck coefficient, are good candidates as new materials in the thermoelectricity field.This paper focus on the exploration of stable tellurium-based glasses and fibers, the preparation of single mode fiber working at the second infrared window (12μm-18μm) for Darwin Project of European Space Agency. The research also includes the investigation of glass composition and preparation technique and their influence on thermal stability, optical thermoelectric properties. The potential applications of tellurium based glasses and optical fibers as novel low-temperature thermoelectrical materials or far-infrared sensing probe are also discussed.To monitor the terrestrial planets and analyze the possibility of extraterrestrial life, Darwin mission (European Space Agency) ask for the development of single mode fiber to detect infrared signatures of H2O (6μm), O3 (9μm), and CO2 (15μm). Previously, only single mode fiber working at the first infrared window (6μm-12μm) has been obtained based on Te-As-Se glasses. This paper focus on the preparation of single mode fiber working at the second infrared window (12μm-18μm) for the detection of CO2. High quality Te-Ge-Se glass preform has been prepared using two-steps purification and capillary method. After drawing, TGS3/TGS5 double index fiber with its core diameter to be 20μm was obtained. It can transmit light from 3μm up to 16μm with the minimum attenuation to be 7.3 dB/m. The output light intensity follows Gaussian distribution, exhibiting single mode propagation.The influence of Ag, I, and AgI on the thermal stability, density, electron conductivity and other properties of GeTe4 glass has been also investiaged after the preparation of (GeTe4)ioo-xMx (M=Ag, I, and AgI) glasses. Among them, (GeTe4)ioo-xAgIx glasses can transmit light up to 35μm. These glasses are very promising materials both as optical fibers for the mid-infrared means, and as lenses for the far-infrared range. On this basis, low-loss Te-Ge-AgI single index fibers were prepared for infrared sensing. Fibers with differenct sensing zone diameter can be obtained by coordinating the instantaneous drawing speed. Sensing experiments of dichloromethane, chloroform, and toluene were carried from 2μm to 16μm. Results show that the tapered fiber-based sensors show an enhanced sensing ability as sensing zone diameter decreases. Besides, the experiment using toluene-isooctane solution show a toluene concentration detection limit of Te-Ge-AgI fiber to be 0.5 vol.%. Other biological or chemical agents such as serum, milk, butter and gasoline are also chosen for exploration of the potential application in daily life. The Te-Ge-AgI infrared sensor is an ideal tool due to its simplicity and efficiency for the identification and quantification of complex system in food safety, medicine, energy, and other areas related to daily life.Otherwise, tellurium-based glasses, due to the intrinsic poor thermal conductivity and high Seebeck coefficient, are good candidates as new materials in the thermoelectricity field. The influence of doping element on glass thermal stability and electrical conductivity has been systematically studied. It has been shown that by introducing copper, the conductivity increases by several orders of magnitude. Among them, (Te85Seis)45As3oCu25 glass has been explored with a combination of a sufficient stability (△T=99℃) and low resistance (p=35 Ω·cm). By sintering this glass with P-type Bio.5Sb1.5Te3, glass-ceramic composites were also obtained using SPS technique.ZT value of glass-ceramics with 30% and 50% of Bio.5Sb1.5Te3 at room temperature is around 0.18. As temperature increase, ZT increased gradually and even reached the values of 0.365 and 0.313 at 413 K respectively.