Annealing Time-Driven Steering of the Structural, Morphological and Optoelectronic Characteristics of Zn-Doped TiO2 Nanostructures

The ability to tailor the bandgap in semiconductor nanostructures from the ultraviolet to visible range is imperative in various light-mediated optoelectronic applications. In this work, Zn-doped TiO₂ nanostructures were prepared and annealed at 350°C for different time intervals such as 1, 2, and 3 h to tailor the band gap. The effects of annealing time on the structural and optical properties of Zn-doped TiO₂ nanostructures were investigated. According to XRD studies, increasing the annealing time authenticates that the dislocation density in the nanostructures decreases, whereas the crystallite size increases. TEM image of the sample annealed at 350°C for 3 h shows the average grain size distribution as 12.33 ± 0.12 nm. The XPS spectrum of the nanostructures that underwent a 3 h annealing at 350°C reveals a broad peak centered at 1021.06 eV, which indicates the Zn²⁺ oxidation state of Zn atoms. The photoluminescence studies indicate that the intensity of UV-visible luminescence bands changes with a rise in annealing time. UV-visible spectroscopic analysis reveals that the band gap increases from 3.32 to 3.36 eV and then decreases to 3.25 eV when the annealing time is raised linearly. Moreover, Zn-doped TiO₂ that has been annealed at 350°C for 3 h has a red shift in the absorption edge and a reduction in the optical band gap, suggesting that it may find application in optoelectronic devices.