Defect-Driven Selectivity Inversion in ZnO Gas Sensors via Y3+ and Dy3+ Doping for Enhanced VOC Detection with a Suppressed NO2 Response

In this work, we demonstrate a defect-mediated strategy to fundamentally reprogram the selectivity of ZnO gas sensors through targeted doping with two types of trivalent rare-earth ions. We incorporate yttrium (Y3+) and dysprosium (Dy3+) into the ZnO host via a high-energy ball-milling (HEBM)-assisted solid-state reaction. On the basis of structural, optical, and spectroscopic characterizations, we demonstrate a significant increase in the oxygen vacancy density and a reduction in the band gap energy. The gas sensing tests revealed a remarkable inversion of selectivity: while doping suppressed the NO2 response by 86% to 94%, it increased the sensitivity to VOCs. Dy doping produced a selective sensor for ethanol (S = 9.61, 5.62 × selectivity over NO2), and Y doping produced a selective sensor for acetone (S = 8.27, 2 × selectivity over NO2). This dopant-specific defect engineering provides a direct pathway to adapt ZnO sensors to the selective detection of VOCs in environmental monitoring.