This study reports the synthesis of erbium (Er)-doped bismuth ferrite (BiFeO3/BFO) nanoparticles at varying molar concentrations (5, 10, and 15 %) using a sol-gel method. X-ray diffraction (XRD) analysis reveals a structural transformation from rhombohedral to orthorhombic upon Er3+ doping, confirming the successful incorporation of Er3+ ions into the BFO lattice. High-resolution transmission electron microscopy (HRTEM) images show that Er-doping leads to a reduction in particle size and a modification of the surface morphology. The bandgap of the Er-doped BFO samples decreases from 2.34 to 2.15 eV with increasing Er content, attributed to the formation of new Er 4f energy levels within the band structure. The magnetic properties of the samples also improve with increasing Er concentration. Photoluminescence (PL) spectra show reduced PL intensity for the 10 % Er-doped BFO sample, indicating a decrease in recombination rates, while electrochemical impedance spectroscopy (EIS) reveals a reduction in charge transfer resistance. Among the samples, the 10 % Er-doped BFO photocatalyst exhibits the highest photocatalytic efficiency. This enhanced activity is attributed to two key factors: efficient separation and migration of photogenerated charge carriers, and a reduced recombination rate of electron-hole pairs, both driven by the rare-earth doping in BFO. Radical trapping experiments further identify hydroxyl (OH•) radicals as the primary species responsible for photocatalytic degradation. This study provides valuable insights into the tunability of BFO's bandgap energy and photocatalytic properties through Er doping.