<p>The incorporation of rare-earth elements into metal oxide nanoparticles is an effective method for tuning their optical and electrical properties, enabling enhanced performance in next-generation photonic and electronic applications. Metal oxide nanoparticles (MONPs) are a class of nanomaterials that have received significant attention due to their wide range of applications. These nanoparticles possess physicochemical properties, such as increased surface area, variable bandgap energies, and improved optical and electrical properties. The use of eco-friendly synthesis methodologies addresses sustainability-related challenges. Copper oxide nanoparticles (CuO NPs) are a subclass of metal oxide nanomaterials with distinctive properties such as a small bandgap, good thermal stability, and catalytic efficiency. The novelty of this research is the environmentally friendly synthesis of Ce-doped CuO NPs and the demonstration of tunable structural, optical, and electrical properties induced by cerium incorporation. Structural, morphological, optical, and dielectric characterizations were carried out to clarify the impact of cerium incorporation on CuO NPs. PXRD analysis verified the presence of a monoclinic CuO crystal structure, while SEM observations revealed nearly spherical nanoparticles with minor agglomeration, and EDX analysis verified successful cerium incorporation. UV–Vis spectroscopy indicated optical bandgap narrowing, and photoluminescence studies suggested defect-related emission behaviour. Dielectric measurements further demonstrated a high dielectric constant and low dielectric loss, which underscores the potential of the synthesized nanoparticles for dielectric and optoelectronic applications.</p>