In this work, black phosphorus was synthesized from a red phosphorus precursor through a solvothermal approach and subsequently converted into phosphorene nanosheets via liquid-phase exfoliation (LPE) in the presence of N-methyl-2-pyrrolidone (NMP). The thinner nanosheets were effectively isolated by reverse cascade centrifugation. X-ray diffraction (XRD) confirmed the formation of the orthorhombic phase with the characteristic (020) peak. Field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), and atomic force microscopy (AFM) revealed the layered morphology and ultrathin thickness of the nanosheets, while energy-dispersive X-ray spectroscopy (EDS) demonstrated their high chemical purity. Raman spectroscopy identified the three characteristic vibrational modes (A1g, B2g, and A2g), highlighting the good crystalline quality of the samples. Optical investigations indicated that reducing the nanosheet thickness induces a significant variation in the electronic bandgap. Photoluminescence (PL) spectroscopy revealed a shift of the emission peak from the near-infrared region in thick multilayer samples to the visible range in phosphorene nanosheets. Furthermore, ultraviolet–visible (UV–Vis) absorption spectra exhibited a blue-shift in the absorption wavelength, corroborating the decrease in the number of layers.