The sol-gel process was employed to successfully synthesize ZnO nanostructures in isopropanol, employing various subcritical temperature and pressure conditions: (90°C, 2 bar), (120°C, 6 bar), (160°C, 14 bar), and (200°C, 30 bar). The resulting products were subsequently annealed at 500°C for 2 hours and subjected to characterization using different analytical techniques, including X-ray diffraction (DRX), infrared (ATR), UV-Visible, and photoluminescence (PL) spectroscopies. The DRX measurements confirmed that the ZnO nanostructures exhibited a polycrystalline structure of the hexagonal wurtzite type. The cell parameters and stresses within the crystallites were found to be influenced by the synthesis conditions (temperature and pressure), in contrast to the particle size. ATR spectra indicated high purity of the produced nanostructures, and it was observed that the position of the absorption band associated with the Zn-O vibrational bond of ZnO shifted towards lower wavenumbers as the temperature increased. UV-Visible spectra demonstrated that the absorption band shifted towards shorter wavelengths with increasing temperature and pressure. The optical gap displayed a similar trend to the lattice parameters and strain within the nanoparticles. PL measurements revealed that the processing temperature and pressure resulted in increased UV emission and decreased visible emission. However, the positions of the UV emission bands were independent of the synthesis parameters.