Effect of the Ce3+ concentration on the crystallite structure and optical properties of ZnO nanomaterials synthesised by sol-gel method

In this study, Ce3+-doped ZnO nanomaterials (Zn1-xO:xCe3+ NPs) were synthesised using the sol-gel method. X-ray diffraction (XRD) pattern and Raman spectra analysis showed that at 1% doping concentration, Zn2+ ions were replaced with Ce3+ ions in the ZnO lattice. However, at higher concentrations (3 and 5%), the CeO2 phase was formed, preventing the diffusion process of Ce3+ ions into the lattice. Field emission scanning electron microscopy (FESEM) images showed that the obtained material had a particle size of several tens of nanometers. X-ray energy dispersive (EDS) spectroscopy and EDS mapping spectra revealed that the synthesised Zn1-xO:xCe3+ NPs had high purity and the Ce element was uniformly distributed in the sample. UV-Vis spectroscopy confirmed the strong interaction between Ce3+ ions and ZnO lattice, leading to increased light absorption in the visible region. The photoluminescence (PL) spectrum of ZnO showed two emission regions peaking at 389 and 650 nm, attributed to band to band recombination and defect types of ZnO such as oxygen vacancy (Vo) and/or oxygen interstitial (Oi), respectively. In comparison with ZnO, the PL spectrum of Zn1-xOx:Ce3+ (x=1-5) samples showed that the visible region emission appeared at new peak at 580 nm originating to the 3d → 4f transition of Ce3+ ions. As the doping concentration increased gradually from 1 to 5%, the 580 nm peak intensity increased, and the 389 peak intensity decreased significantly, indicating that Ce3+ ions inhibited the NBE recombination process of ZnO. This study suggested that Ce3+ doped ZnO NPs have a great potential for application in visible-light photocatalysis.