Structural and optical properties of Iodine doped zinc oxide nanoparticles

Iodine- doped zinc oxide (viz., ZnO_1-xI_x) nanoparticles were prepared using the sol–gel method. The samples were treated at 700 °C in air for 1h. The structural, morphological and optical properties were measured using an X-ray diffractometer (XRD), a field emission scanning electron microscope (FE-SEM), UV–visible spectroscopy (UV/vis) and Raman spectroscopy, respectively. XRD results showed that the pure and doped samples have a wurtzite hexagonal structure, indicating the presence of some impurities in doped samples. The lattice parameters a and c were observed to be closer to the reported values for pure ZnO^. The average crystalline size values of samples were calculated and found to be between 84 ± 18 and 177 ± 53 nm. The FE-SEM micrographs reveal that the particle sizes decreased from 77 to 57 nm with an increasing I concentration from x = 0.0 to x = 0.4, respectively. The morphologies of the samples were changed from particle to flask shape at higher I concentrations of 0.6 and 0.8 with average diameters of 213 and 427 nm. The increasing I concentration from 0.0 to 0.8 narrows the optical energy gap (E_g) from 3.271 to 3.242 eV due to the presence of oxygen vacancies or the lattice expansion caused by doping. Raman spectra of samples consist of the E₂(high) mode, which confirmed the wurtzite hexagonal structure and it is located between 435 and 436 cm⁻¹ except for x = 0.6, where the E₂(high) mode was shifted to the higher wavenumber could be due to defects or anisotropic internal strains consistent to different growth directions.