<p>Herein, the polyvinylidene fluoride (PVDF) is the Erbium oxide (Er₂O₃) nanoparticle host matrix. The PVDF-Er₂O₃ membranes are fabricated via the casting method. The fabricated membranes are characterized using X-ray diffractometer (XRD) and Fourier transform infrared (FTIR). XRD data showed the existence in the PVDF matrix of α and β phases. The XRD and FTIR confirmed the promotion of the β-phase and suppression of the α-phase as the Er₂O₃ concentration increased in the PVDF membrane. Furthermore, the optical characteristics of the PVDF membrane change with the enhancement of the β-phase accordingly. The UV–Visible absorbance data are recorded for the Er₂O₃-doped PVDF membranes, and the optical constants are determined. The optical bandgaps direct/indirect are 5.44/4.58 eV for the PVDF membrane, which is reduced to 4.75/3.85 eV for the 8% Er₂O₃-doped PVDF membrane. The linear refractive index was computed, showing an increase in the refractive index from 1.9371 to 2.0386 for pure PVDF and 8% Er₂O₃-doped PVDF membranes, respectively. Also, the nonlinear optical constants, including 1st- and 3rd-order optical susceptibility and nonlinear refractive index, were investigated and showed with increasing Er₂O₃ concentration an enhancement in the PVDF matrix.</p>