Solar driven photocatalytic properties of Sm3+ doped ZnO nanocrystals

Abstract ZnO nanocrystals (NCs) doped with different Sm3+ concentrations were prepared by sol gel method. XRD analysis showed that the ZnO:Sm3+ NCs crystallized in the hexagonal wurtzite structure with a grain size varying from 61.4 nm to 72.6 nm, with Sm3+ concentration. Transmission electron microscopy (TEM) images indicated that ZnO NCs adopted a bimodal size distribution. X-ray photoelectron spectroscopy (XPS) revealed that Sm ions existed in trivalent state and substituted at the Zn2+ sites in the ZnO lattice. Raman spectra highlighted the presence of the LO mode, confirming the successful substitution of Zn2+ by Sm3+. Excitation and emission spectra highlighted the typical 4f-4f transitions of Sm3+. A photoluminescence (PL) quenching accompanied by a decrease of PL lifetime was observed for Sm3+ concentrations above 1.5%. The processes of excitation and de-excitation of the Sm3+ ions in ZnO NCs were discussed based on dipolar interactions between the excited ions. The ZnO:Sm3+ (1.5%) photocatalyst induced complete and fast photodegradation of RhB under sunlight irradiation. The photocatalytic mechanism is discussed based on the analysis of PL lifetimes. The role of oxygen vacancies on the reduction of Sm3+ ions and its impact on the photocatalytic process is also discussed.