Role of Oxygen Vacancy Sites on the Temperature-Dependent Photoluminescence of SnO2 Nanowires

The role of oxygen vacancies in temperature-dependent photoluminescence of SnO2 nanowires was investigated by X-ray absorption spectroscopy. Two types of oxygen vacancies are present in the nanowires: at out-of-plane sites and at in-plane sites; both play crucial roles in the temperature dependence of the photoluminescence. Oxygen vacancies at in-plane sites participate in photon emission at low temperature, whereas those at out-of-plane sites result in photoluminescence at room temperature. Accordingly, the luminescence color changes from orange (630 nm, 1.93 eV) to green (515 nm, 2.4 eV) at 100 K. The color change is accompanied with a notable change in the oxygen K-edge X-ray absorption spectra. The scanning transmission X-ray microscopy results indicate that more oxygen vacancies at in-plane sites are present in the surface region than in the bulk region, whereas more oxygen vacancies at out-of-plane sites are present in the bulk region than in the surface region. Overall, the results demonstrate that oxygen-vacancy-mediated fluorescence properties of SnO2 nanowires are temperature-dependent; i.e., the photoluminescence mechanisms of the nanowires are mediated by oxygen vacancies at different sites, and the bicolor fluorescence originates from charge transfer between the states.

Automated summary

The investigation of temperature-dependent photoluminescence of SnO2 nanowires revealed that oxygen vacancies at different sites play crucial roles in the emission process. Oxygen vacancies at in-plane sites are responsible for photon emission at low temperature, while those at out-of-plane sites lead to photoluminescence at room temperature. The color change in luminescence is accompanied by a notable change in the oxygen K-edge X-ray absorption spectra, indicating the temperature-dependent nature of oxygen-vacancy-mediated fluorescence properties of the nanowires.