Abstract
<title>Abstract</title> <p> In this study, pure CuO, pure ZrO <sub>2</sub> nanoparticles (NPs) and CuO/ZrO <sub>2</sub> nanocomposite (NC) were synthesized via a solution assisted hydrothermal method at 150 <sup>ᵒ</sup> C and systematically investigated to understand the influence of CuO incorporation on the structural, optical and luminescence properties of ZrO <sub>2</sub> . X-ray diffraction analysis confirmed the formation of monoclinic CuO and predominantly monoclinic ZrO <sub>2</sub> , while the CuO/ZrO <sub>2</sub> NC exhibited partial stabilization of the tetragonal ZrO <sub>2</sub> phase. Williamson‒Hall (WH) analysis revealed reduced lattice strain and dislocation density in the CuO/ZrO <sub>2</sub> NC. The average crystallite sizes were found to be 14.2 nm for CuO, 8.4 nm for ZrO <sub>2</sub> and ⁓38 nm for the CuO/ZrO <sub>2</sub> NC. SEM revealed agglomerated micron-sized particles assembled from nanoscale crystallites, while EDAX analysis confirmed the homogeneous distribution of Cu, Zr and O elements. FTIR spectra showed characteristic Cu‒O and Zr‒O vibrational modes, together with band broadening in the composite arising from interfacial interactions between the constituent oxides. DRS studies revealed optical band gaps of 2.44 eV for CuO, 4.04 eV for ZrO <sub>2</sub> and 3.64 eV for the CuO/ZrO <sub>2</sub> NC, indicating significant modification of the electronic structure after composite formation. PL studies demonstrated defect‒assisted visible emissions associated with oxygen-vacancy-related states and interfacial defect centers. The combined structural and spectroscopic analyses revealed a strong correlation between phase evolution, microstructural modification and optical response, which may enhance the potential of CuO/ZrO <sub>2</sub> NCs for photocatalytic, sensing and optoelectronic applications. </p>