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Undoped and codoped (Eu/Na) ZnO nanocrystals (NCs) were successfully manufactured through an economical sol-gel method. X-ray diffraction (XRD) analysis demonstrated pure hexagonal wurtzite structure without secondary phases for all the samples. The size of the NCs was found to decrease with codoping by Eu³⁺/Na⁺ which is related to the existence of strain and stress in the lattice. The dominance of the E₂(high) mode in Raman spectra indicates the good crystallinity of the samples. The study from the X-ray photoelectron spectroscopy (XPS) shows the successful insertion of both Eu³⁺ and Na⁺ ions into the ZnO lattice and the generation of the zinc and oxygen vacancies (Vo) defects. The band gap energy was reduced and the Urbach energy increased with Na⁺ content, proving the distortion of the lattice. From the photoluminescence (PL) study, the activation of the Eu³⁺ ions by Na⁺ ones was evidenced. Longer PL lifetimes were obtained from Eu³⁺ ions when they were sensitized by Na⁺, which may be beneficial to several applications. A process of excitation transfer from both the ZnO host and Na⁺ sensitizers to the Eu³⁺ ions was evidenced and discussed. As an application, we tested the performances of the prepared NCs as photocatalysts for Rhodamine B photodegradation under sunlight irradiation. The ZnO NCs codoped with 1% Eu/4% Na displayed the best photodegradation rate with a good stability and a high kinetic rate constant <i>k</i> of 0.021 min⁻¹. The photocatalytic mechanism is discussed in terms of longer radiative recombination from Eu³⁺ and the generated oxygen vacancies.