In Situ PL Tracking the Evolution and Functionality of Oxygen Defects in the In 2 O 3 -Based NO 2 Gas Sensor

Oxygen defects, including oxygen vacancies (V O •• ) and interstitial oxygen (O i ″), are one of the main factors affecting the gas-sensing performance of metal oxide semiconductors. Therefore, in situ investigation of the intrinsic roles of oxygen defects during the gas sensing processes is of great importance to disclose the gas sensing mechanism for MOS-based gas sensors and improve the performance of the sensors. Herein, we synthesized pristine In 2 O 3 single-crystal porous nanosheets by the hydrothermal method and subsequently modulated the oxygen defects via Ho/Pr single and binary doping. The evolution of the oxygen defects during the gas response of sensors was tracked in real time by in situ photoluminescence (PL). The gas sensing test indicated that the Ho/Pr–In 2 O 3 gas sensor improved the response to 10 ppm of NO 2 from 8.5 to 37.5 at lower power consumption than pristine In 2 O 3 while providing higher stability and selectivity. In situ PL results also confirmed the functionality of oxygen defects: the facilitative impact of V O •• and the inhibitory effect of O i ″ on ion-adsorbed oxygen. Besides, a positive relationship between the sensor’s response and the concentration of V O •• was established in this study.