<p>In this study, the co-precipitation method was employed to synthesize ZnO samples with varying Er concentrations (0%, 1%, 2%, &amp; 3 wt.%). X-ray diffraction (XRD) analysis confirmed the presence of the hexagonal wurtzite structure of ZnO with increased crystallite size of 60 nm for ZnO:Er 1 wt.%. Fourier transform infrared (FT-IR) spectroscopy validated the structural coordination and identified various organic functional groups within the framework of ZnO of all the prepared samples. The morphology of the prepared ZnO:Er samples, as observed through field emission scanning electron microscopy (FESEM), revealed nanorod platelet-shaped grains with clear grain boundaries. The optical properties indicated a lower band gap of 3.25 eV for ZnO:Er1% sample. The analysis of light emission through photoluminescence (PL) spectroscopy showed distinct peaks in the range of about 325–475 nm and at 615 nm. The ZnO sample containing 1% Er exhibited a more intense orange emission peak, which indicates a higher concentration of oxygen vacancies in the material. The response of the ZnO:Er1% sensor increased with higher ammonia concentrations, ranging from 50 to 250 ppm, and exhibited excellent stability over 50 days, indicating a strong interaction with the sensor. Among the fabricated ammonia gas sensors, ZnO:Er1% showed the maximum gas response of 403 at 250 ppm of NH₃, with superior response and recovery times of 7.7 s and 8.0 s, respectively, at ambient temperature. This demonstrates the high potential of ZnO:Er1% for commercial gas sensing applications.</p> Graphical Abstract <p></p>