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

Abstract

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% Tb-doing 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 (O_v). 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.