Remarkable NH3 gas sensing performance of spray deposited Tb doped WO3 thin films at room temperature

To evade potential health hazards associated with exposure to NH3, there has been an increasing demand for efficient gas sensors operating at room temperature (RT). In this study, thin films of Tb-doped (0-5 wt%) WO3 synthesized by spray pyrolysis technique are used as a novel material for sensing NH3 gas. The X-ray diffraction (XRD) pattern identified the hexagonal crystal system of WO3 films and increased crystallinity for the 2 wt% Tbdoing concentration. Field emission scanning electron microscopy (FE-SEM) unveiled the distinct surface morphology of mesh-like porous structures for Tb-doped films suitable for the target gas adsorption/desorption process. Multiple photoluminescence (PL) emission peaks indicate the presence of defect states, including defect energy levels created by oxygen vacancies (Ov). Optical analysis indicated shrinkage of the bandgap of WO3 thin films for doping levels up to 2 wt%. Among all gas sensors, 2 wt% Tb-doped WO3 exhibited exceptionally high response and low response time at 250 ppm NH3 concentrations measured at room temperature (RT). The sensor's performance for NH3 gas sensing is compared with previous reports on WO3-based NH3 sensors. The gas sensing mechanism in WO3 is also briefly discussed.