Contribution of oxygen-vacancy defect-types in enhanced CO2 sensing of nanoparticulate Zn-doped SnO2 films

In spray deposited nanocrystalline SnO2 films, large number of defects involving vacancies and interstitials exist. Doping SnO2 lightly with zinc introduces new Sn2+ states and in fact more oxygen vacancies for charge compensation, which promotes the increase in concentration of chemisorbed oxygen. As the deposition temperature is higher, the XRD and HRTEM results exhibit a clear preferred (110) orientation. The Zn2+ doping in SnO2 introduces new surface and structural oxygen defects, as apparent from Raman and Photoluminescence analysis. The doping alters the polarization of atoms, as seen from the widening in Raman lines. Decreased UV emission peaks (similar to 333 nm) can be attributed to enhanced crystallization and the incited oxygen vacancy (OV) defects. A dominant blue-green luminescence peak centered at 495 nm reveals the formation of deep trap, due to in-plane OVs. The red-shift in PL broad yellow-shoulder at 556 nm features an increase of deep oxygen defect energy levels occurring on the surface of the nanocrystal films. On doping, involvement of the defect composition and the contribution of different kinds of OVs play important roles in enhancing CO2 sensing response of 94.4% to 500 ppm. In 2.4 wt% Zn doping at 310 degrees C, the in-plane OVs are found to dominate over bridging OVs.