Room-temperature nitrogen-dioxide sensors based on ZnO 1- x coatings deposited by solution precursor plasma spray

tThe stoichiometric ZnO has a bandgap greater than 2.6 eV and has no or weak response to visible light,which greatly suppresses its applications. We report here that a process of solution precursor plasmaspray (SPPS) can effectively narrow the bandgap and extend the absorption of ZnO to visible light region,which mainly results from highly concentrated oxygen vacancies generated during SPPS process. By pho-toluminescence spectroscopy, electron paramagnetic resonance and X-ray photoelectron spectroscopy,we found that a large number of oxygen vacancies were implanted into ZnO1-xprepared by SPPS. The gen-eration of highly concentrated oxygen vacancies were mainly attributed to reducing atmosphere as wellas fast heating and cooling process inherently provided by SPPS. The findings of this work create a newway for developing narrow bandgap ZnO1-x. We present that the SPPS ZnO1-xcoatings can be utilizeddirectly as sensitive materials under visible-light illumination. The oxygen vacancies have considerableinfluence on its optical and electrical properties. The ZnO1-xcoatings exhibited an obvious absorptioncovering the whole visible-light region and its bandgap was calculated to be 2.15 eV which was muchnarrower than that of stoichiometric ZnO (3.37 eV). The sensors based on ZnO1-xcoatings showed sig-nificant responses to NO2at room temperature. In addition, the sensor response increased linearly withNO2concentration. The enhanced sensor properties were attributed to the rich oxygen vacancies andspecial coating microstructure provided by SPPS.