A facile one-step hydrothermal synthesis to prepare cerium (Ce³⁺) ion doped CdSe/CdS core/shell quantum dots (QDs) is introduced. The effect of Ce³⁺ ion doping on structural and optical properties of the CdSe/CdS core/shell QDs is comprehensively investigated. With increasing Ce doping concentration, a linear increase in the lattice parameter is observed, suggesting the successful coupling of Ce³⁺ ions to the CdSe/CdS QDs. X-ray photoelectron spectroscopy reveals strong peaks of the Ce³⁺ state, indicating that Ce is initially present mainly in the Ce³⁺ ion state. In addition, red-shift over the range 538–569 nm is observed in the photoluminescence (PL) spectra of Ce³⁺ ion doped CdSe/CdS QDs. Results clearly indicates that the PL peak positions of the CdSe/CdS QDs could be controlled by the Ce content. This study highlights a new approach to tune the emission of the QDs.