Ag–CdS-Coated Cladding-Modified Fiber-Optic Sensor for Detection of NO2 Gas.

In this study, a cladding-modified fiber-optic sensor is reported for NO2 gas detection. Monitoring the purity of air is the need of the hour, with the growing technologies. Hence, in this work, Ag-doped CdS is coated over the cladding-removed region of 3 cm length by Chemical Bath Deposition (CBD) which acts as the gas-sensing medium. Ag–CdS is coated over four fibers each with a different coating duration of 10 min, 20 min, 30 min and 40 min. Characterization of Ag–CdS is done by Scanning Electron Microscope (SEM), UV-visible absorption spectroscopy and UV-visible reflectance spectroscopy. The spectral response for different concentrations of NO2 is studied on the four fibers separately, and it is analyzed and compared. The minimum detection limit is 100 ppm and the response time is 10 min. Out of the four fibers, Ag–CdS-30 exhibited the best response with a sensitivity of 15.5%. The results are compared with cladding-modified fiber coated with CdS, which was reported previously. The effect of Ag-doping is analyzed. Ag-doped-CdS was coated over cladding-removed region of optical fibers, with the same coating durations used for CdS. Among these optical fibers, Ag-CdS-30 exhibited best response towards NO2 gas. But the sensitivity of CdS-20 was higher when compared with Ag-CdS-30. To understand the reasons for its better performance, certain properties of both the materials were analysed. [ABSTRACT FROM AUTHOR]