UV emitting ZnO nanopowder was chemically synthesized and subsequently subjected to heat treatment in oxygen atmosphere for potential optoelectronic properties. Characterization including Raman spectroscopy, photoluminescence, SEM, FT-IR and XRD were performed to see the effect of high temperature heat treatment and subsequently oxygen defects on the physical properties of ZnO powder. Chemically prepared product was highly pure polycrystalline w-ZnO with random crystallites orientation. Study showed a magnificent absorption of oxygen by the product as manifested by the decreased intensity of deep-level green emission and E₁ (LO) phonon mode. The phonon modes appeared at 276 and 970 cm⁻¹ and which have been assigned to ZnO by the previous researchers under relaxed Raman selection rule were no longer found with heat treatment. UV emission was enhanced and the ratio of UV to green emission (𝐼_UV/𝐼 _green) was correlated with the crystal structure and oxygen vacancies before and after heat treatment. FT-IR study established strong Zn-O bending and stretching bands at 356 and 498 cm⁻¹. SEM analysis demonstrated fine crystallites distribution in ZnO nanopowder with almost spherical morphologies. Reasonably, a more spherical and ordered morphologies with large grains were found with heat treatment. The investigated findings manifested improved structural and optical properties for various optoelectronic and biomedical applications of technological importance.