Ag-doped ZnO nanorods for multifunctional applications: UV and ethanol gas sensing

The effect of silver dopant concentration (0.4, 0.6, 0.8, 1, and 1.2 mol%.) on the room temperature dual performance of ZnO nanorods for sensing the UV light and ethanol vapor targets was examined. Pure and Ag-doped ZnO nanorods were grown by using the hydrothermal synthesis method on SnO₂:F-coated glass substrates. The morphology, crystal structure, and optical properties of nanorods were investigated by using scanning electron microscopy, X-ray diffraction patterns, transmission electron microscopy (TEM), diffuse transmission and reflectance spectroscopy, and temperature-dependent photoluminescence spectroscopy. TEM results showed that Ag-related nanoparticles were embedded in ZnO nanorods. X-ray photoelectron spectroscopy was employed to examine the surface composition of pure and Ag-doped ZnO nanorods, which demonstrated Ag incorporation at Zn lattice sites (\(Ag_{{Zn}}\)) on the surface of nanorods. The values of bandgap energies estimated from Tauc plots determined by applying Kubelka–Munk function and near band edge emission in photoluminescence spectra are consistent with each other. The UV light and gas sensing measurements separately indicated the sensitivity improvement of ZnO nanorods by silver doping. The samples with the Ag/Zn molar ratio of 0.8 had the highest response value under 365 nm UV light illumination, the shortest rise and decay times, and the highest sensitivity to ethanol vapor at room temperature. At this optimum value of dopant concentration, the UV responsivity of pure nanorods increased from 0.97 to 5.09 mA/W by doping, at 5 V. At this voltage, the UV sensing rise and decay times reduced from 3.94 and 194.61 s to 3.12 and 102.85 s, respectively. Moreover, the room-temperature ethanol vapor response of nanorods enhanced from 4.66 to 8.7%. The mechanism of room-temperature dual sensing of UV light and ethanol vapor was discussed.