NO₂ gas-sensor based on erbium-doped ZnO nanorods: experimental validation and theoretical analysis

In this study, we synthesized erbium-doped ZnO nanorods via a hydrothermal method and evaluated their NO₂ gas sensing performance. The incorporation of Er and formation of well-defined nanorods were confirmed by XRD, FESEM, EDS, FTIR, Raman, and UV–vis spectroscopy. The sensor exhibited optimal response at 200 °C with a response value of 6.3 to 100 ppm NO₂, a rapid response time of 30 s, and excellent repeatability and selectivity. The enhanced performance is attributed to Er³⁺/Er²⁺ redox cycling, which generates reactive oxygen species and promotes charge transfer, as confirmed by DFT calculations. Theoretical analysis revealed that Er doping introduces defect states within the ZnO band gap and significantly enhances NO₂ adsorption energy (−3.51 eV) and charge transfer (0.87 |e|), corroborating the experimental selectivity pattern. This work provides a novel integration of experimental and theoretical approaches, offering new mechanistic insights into lanthanide-enhanced gas sensing and establishing Er-doped ZnO nanorods as promising candidates for advanced NO₂ sensors.