Optical and photocatalytic properties of rare earth metal-modified ZnO quantum dots

A series of novel ZnO quantum dots modified with rare earth metals was successfully prepared by a simple solgel approach. The effects of types (Eu, Er, Tb, Yb, Ho, La) and amounts (from 0.09 to 0.45 mmol) of lanthanides on the optical properties, structural characterization and photocatalytic activity of ZnO/RE QDs were systematically investigated. The X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) with energy dispersive X-ray analysis (EDX) and UV-Vis diffuse reflectance spectroscopy were used to characterize surface properties, while photoluminescence (PL) emission spectroscopy and UV-Vis-driven degradation of phenol in aqueous phase were applied to understand optical and photocatalytic properties. The experiments demonstrated that generally modification of ZnO QDs by lanthanides resulted in increase of photoactivity while photoluminesce decrease at the same moment. The highest photocatalytic activity among all obtained nanomaterials and the lowest photoluminescence quantum yield among ZnO/Er photocatalysts were observed for ZnO QDs modified with 0.09 mmol of erbium. Increased photocatalytic activity has been shown in successive samples: ZnO/0.09_Er > Zn0/0.18_Eu > Zn0/0.09_La > Zn0/0.27_Er > ZnO/0.18 Tb > pristine ZnO QDs. The experimental results were supported by calculations based on density functional theory (DFT) which revealed atomic and electronic structure of Er/La modified ZnO QDs.