Effect of zinc doping on the bandgap and photoluminescence of Zn2+-doped TiO2 nanowires

This study was focused on the effect of Zn2+ dopant concentration on the absorption edge and photoluminescence of anatase TiO2 nanowires synthesized by hydrothermal technique. For the undoped anatase TiO2 nanowires, the indirect band gap of 3.26 eV and the direct band gap of 3.58 eV are assigned to the indirect Gamma(3) -> X-1b and direct X-2b -> X-1b transitions, respectively. The Zn2+-doping makes the absorption edge of TiO2: Zn2+ nanowires shift towards the lower energy side (red shift). On the other hand, the replacing Ti4+ ions with Zn2+ ions creates oxygen vacancies (V-O) and shallow defects associated with V-O. Just these defects are responsible for the enhanced luminescence of Zn2+-doped TiO2 nanowires.