Enhanced photoluminescence and structural properties of Zn-doped anatase TiO2 nanoparticles

Undoped and zinc-doped TiO2 nanoparticles (NPs) were synthesized by the sol–gel method. The XRD spectra revealed that both synthesized undoped and Zn-doped TiO2 NPs remain in the anatase phase after calcined at 500 °C. The crystallite size was increased from 17 to 52 nm as the Zn content was increased from 0 to 0.2 mol%, which implies also a decrease of the micro-strain and surface area. The agglomerated spherical-like morphology with a diameter of roughly 10–20 nm was shown by SEM and TEM micrographs. The bandgap values were found to be decreased from 3.2 to 3.0 eV when Zn concentration increased from 0 to 0.2 mol%. A reduction in bandgap with an increase in dopant concentration may due to the increased in crystallite size along with enhanced lattice parameters (i.e., a and c) and d-spacing. From PL spectra, all samples exhibited a broad emission band in the visible region of about 400–500 nm centered at 430 nm. The highest PL emission was obtained for 0.2 mol% Zn doping. The broad PL emission over the visible range is greatly reduced at 0.4 mol% Zn due to concentration quenching. It is suggested that the Zn2+ doping induced oxygen vacancies which could promote the photoluminescence processes.