<p>In this study, Bi_1-xRE_xFe_1-xAl_xO₃ nanoparticles, co-substituted with various rare earth (RE) and Al ions, were synthesized using the sol-gel method. The structural, optical, and magnetic properties of the synthesized nanoparticles were thoroughly characterized using X-ray diffraction, Raman spectroscopy, Fourier-transform infrared spectroscopy, and magnetic measurements. The optical band gap of the nanoparticles exhibited significant variation with co-substitution. The photocatalytic properties of the nanoparticles were investigated through the photocatalytic degradation of methyl orange dye under sunlight irradiation. The co-substitution with RE and Al ions significantly enhanced the photocatalytic degradation efficiency of the nanoparticles, reaching up to 98.5% after 100 min. of irradiation. This work highlights the potential of Bi_1-xRE_xFe_1-xAl_xO₃ nanoparticles as efficient and robust photocatalysts for applications such as water purification and environmental remediation.</p> Graphical Abstract <p></p>