In this article, CuO nanoparticles have been synthesized successfully using the facile hydrothermal approach with various reaction temperatures (60–220 °C). The structural, optical, compositional, and morphology are studied using various analytical techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), diffuse reflectance spectroscopy (DRS), energy-dispersive X-ray analysis (EDAX), laser Raman spectroscopy, and photoluminescence (PL) spectroscopy. The X-ray diffraction pattern revealed pure CuO with monoclinic structure, and the laser Raman study supports XRD results. The FTIR analysis confirmed a pure CuO phase, and elemental studies confirm the CuO stoichiometry. The optical band gap was estimated in between 1.46 and 1.53 eV, and the band gap values are varied due to grain size. The FESEM images reveal those different morphologies such …