We have reported on the synthesis of CuO nanostructures via a complex precipitation method using NH3·H2O as a complexing agent. Synthesized nanostructures were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), Luminescence spectroscopy and UV-Vis-NIR spectroscopy. Structural studies revealed that the formation of CuO nanostructures with monoclinic Crystal structure. The crystallite size of CuO nanostructures was estimated to be ˜30 nm using Debye–Scherrer’s formula. Morphological analysis by Field Emission scanning electron microscopy showed the formation of CuO architecture. The optical band gap value was estimated to be 1.6 eV using Tauc’s plot. The light harvesting efficiency of CuO in dye solution of Catharanthus Roseus plant leaves is also discussed. Photoluminescence spectroscopy has been employed in order to explore the optical emission properties of CuO nano particles.