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This study investigates the gas-sensing performance of thin films doped with varying Er concentrations (0–5 wt.%) synthesized via nebulizer spray pyrolysis (NSP). X-ray diffraction (XRD) confirmed the formation of anatase TiO 2 , with crystallite size increasing to 45 nm for the TiO 2 :Er (4 wt.%) film. FESEM analysis revealed uniformly distributed spherical grains, with the largest particle size also observed at 4 wt.% Er. Optical transmittance measurements showed high transparency of ∼80% in the visible region, while the optical bandgap varied from 3.43 to 3.59 eV, reaching its maximum for the 4 wt.% Er-doped film. Photoluminescence spectra exhibited enhanced emission intensity at 4 wt.%, indicating increased oxygen vacancies and higher recombination rates of photoinduced carriers. Gas sensing studies demonstrated a significant improvement in NH 3 detection at room temperature, with the TiO 2 :Er (4 wt.%) film achieving a peak response of 70 at 250 ppm, along with rapid response and recovery times of 3 s and 6.3 s, respectively. These results highlight the TiO 2 :Er (4 wt.%) thin film as an efficient and stable NH 3 sensor, emphasizing the effectiveness of rare-earth doping for enhancing metal oxide gas sensor performance. 1 Novel TiO 2 :Er thin films were developed by the NSP route for harmful gas sensing applications. 2 FESEM analysis showing homogenous spherical shaped grains with the highest particle size for the TiO 2 :4 wt.%Er film. 3 Optical studies indicated ∼80% transparency in the visible region with the highest bandgap for TiO 2 :4wt.%Er film. 4 At room temperature, the TiO 2 :4wt.%Er samples displayed excellent NH 3 gas response; it exhibits a peak response of 70% at 250 ppm. 5 TiO 2 :4wt.%Er film-based device also demonstrated outstanding stability, repeatability, and response/recovery time of 3/6.3s, making it a promising candidate for NH 3 detection in practical applications.