The effect of Zr (IV) doping on TiO2 thin film structure and optical characteristics

Dense thin films of TiO2 and TiO2 doped with Zr4+ were spin coated on glass substrate and annealed at 450 °C. The optical characteristics and crystalline structure were studied using UV–vis, PL, XRD, and SEM. X-ray investigation proved that an anatase phase was formed in all Zr-doped samples (0, 0.5, 1, 5, and 10 %). Zr-doping changes the band gap energy from Eg = 3.48 eV (undoped) to 3.57 eV (1 % doping), along with the large size of Zr4+ results in slight lattice enlargement. Increasing Zr-doping beyond 1.0 % is associated with decreasing the band gap due to amorphization of TiO2. The anatase crystallites growth is stalled with increasing doping; from 23.5 nm to 10.43 nm and micro-strain increases with increasing doping concentration. The changes in optical properties, crystal growth and structure properties are due to lattice strain created by the collective effect of Zr-doping and reduction in crystallite size. Zr-doped TiO2 nanoparticles exhibited typical photoluminescence (PL) matching to the visible spectrum region when excited at 275 nm. The produced thin films had a lower rate of electron–hole recombination than TiO2 that was not doped.