Enhancing the optical emission of cerium oxide nanoparticles is essential for potential biomedical applications. In the present work, we report a simple chemical precipitation technique to synthesize europium-doped cerium oxide nanostructures to enhance the emission properties. Structural and optical properties showed an acute dependence on the concentration of oxygen ion vacancy and trivalent cerium, which, in turn, could be modified by dopant concentration and the annealing temperature. Results from X-ray photoelectron spectroscopy showed an increase in tetravalent cerium concentration to 85% on annealing at 900 degrees C. The concentration of oxygen ion vacancy increased from 1.7x10(20) cm(-3) to 4.1x10(20) cm(-3) with the increase in dopant concentration. Maximum emission at room temperature was obtained for 15 mol % Eu-doped ceria, which improved with annealing temperature. The role of oxygen ion vacancies and trivalent cerium in modifying the emission properties is discussed.