In this study, pure cadmium oxide (CdO) nanoparticles as well as a mixed gadolinium oxide (Gd2O3)/CdO nanocomposites with mixing contents (0% ≤ Gd2O3 content ≤ 15%) were synthesized via facile precipitation technique followed by calcined treatment. The synthesized nano-powders were characterized by various techniques in terms of their structure, morphology, composition, and optical properties. X-ray diffraction analysis illustrated that all samples have high cubic phase purity and well crystalline nature. The as-synthesized CdO nanoparticles exhibited only the expected Bragg peaks for a single-phase cubic crystal structure of pure CdO. The Gd2O3/CdO mixed oxide nanocomposites gave rise to a Gd2O3 cubic phase in addition to the cubic phase of pure CdO. Further support for the formation of highly pure CdO and Gd2O3 phases was obtained via infrared (IR) spectroscopy. The morphologies of pure CdO and mixed Gd2O3/CdO nanoparticles were probed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which showed that the collected samples consist of individual semi-spherical shaped entities with different particle sizes (23-31 nm). The optical band gap (Eg) of powdered samples was calculated using UV–Vis diffuse reﬂectance spectroscopy (UV–Vis DRS) analysis according to the Kubelka–Munk theory. Importantly, the results showed that the Eg values increased from 2.76 eV to 3.92 eV upon increasing the Gd2O3 content. 3D fluorescence analysis showed that, the quenching in the emission peak intensity with increasing Gd2O3 content is due to the high separation efficiency of photogenerated electron-hole pairs.