Slow response and recovery kinetics is a major challenge for practical room-temperature NO2 gas sensing. Here, we report the use of visible light illumination to significantly shorten the response and recovery times of a PbSe quantum dot (QD) gel sensor by 21% (to 27 s) and 63% (to 102 s), respectively. When combined with its high response (0.04%/ppb) and ultralow limit of detection (3 ppb), the reduction in response and recovery time makes the PbSe QD gel sensor among the best p-type room-temperature NO2 sensors reported to date. A combined experimental and theoretical investigation reveals that the accelerated response and recovery time is primarily due to photoexcitation of NO2 gaseous molecules and adsorbed NO2 on the gel surface, rather than the excitation of the semiconductor sensing material, as suggested by the currently prevailing light-activated gas-sensing theory. Furthermore, we find that the extent of improvement attained in the recovery speed also depends on the distribution of excited electrons in the adsorbed NO2/QD gel system. This work suggests that the design of light-activated sensor platforms may benefit from a careful assessment of the photophysics of the analyte in the gas phase and when adsorbed onto the semiconductor surface.
Keywords: NO2 sensor; light activation; quantum dot gel; quantum embedding method; room-temperature gas sensing.