Origin of low-temperature photoluminescence from SnO2 nanowires fabricated by thermal evaporation and annealed in different ambients

Rutile (110) tin dioxide nanowires synthesized by thermal oxidation of tin powders and having a band gap of 4.2eV were annealed in vacuum and O2 at 600°C for 1h. The photoluminescence (PL) properties of the as-grown and annealed samples were measured from 10to300K. The nanowires annealed in O2 showed weak luminescence at 393nm at temperatures below 100K, and no luminescence could be detected at temperatures higher than 100K. In contrast, the nanowires annealed in vacuum exhibited strong luminescence at 480nm at temperatures lower than 100K and at 600nm when the temperature was higher than 100K. Our PL results show that the emissions originate from the defect electronic states in the band gap formed by surface oxygen vacancies and solve the long-time controversy over the origin of the luminescence.