The PL emission spectra of undoped and Ceria doped ZnO samples taken at room temperature and excitation wavelength of 350 nm are shown in Figure Emission peaks at 420, 440, and 470 nm were observed. A broad PL emission signal is observed in the visible region, which may be due to the defects and recombination of photogenerated holes and electrons. The broad peak also corresponds to zinc vacancies and singly and doubly charged oxygen vacancies As the conduction band (CB) and valence band (VB) potentials of CeO2 are both more negative than those of ZnO, a heterojunction is formed when the band edge positions of CeO2 and ZnO have matched . The schematic of the proposed mechanism is shown in Figure . When Ce-ZnO is excited by UV light with a wavelength more than the band gap of the composite, an electron from the valence band jumps to the conduction band leaving behind a hole in the valence band. The CB of CeO2 being higher than that of ZnO, the photogenerated electrons from CeO2 are transferred to the CB of ZnO due to the potential difference between them which in turn enhances the charge transfer mechanism, thereby promoting the photocatalytic activity .