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 4.2 eV were annealed in vacuum and O-2 at 600 degrees C for 1 h. The photoluminescence (PL) properties of the as-grown and annealed samples were measured from 10 to 300 K. The nanowires annealed in O-2 showed weak luminescence at 393 nm at temperatures below 100 K, and no luminescence could be detected at temperatures higher than 100 K. In contrast, the nanowires annealed in vacuum exhibited strong luminescence at 480 nm at temperatures lower than 100 K and at 600 nm when the temperature was higher than 100 K. 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.