This study investigates the influence of Yb co-doping on the photocatalytic performance of 2% Er-doped BiVO4 nanoparticles under infrared light for wastewater treatment. Er/Yb co-doping induces a phase transformation from monoclinic to tetragonal BiVO4, significantly enhancing infrared light absorption and photocatalytic activity. The optimal Yb concentration for maximizing activity is found to be 2%, achieving a one-order-of-magnitude improvement compared to undoped BiVO4. Up-conversion processes involving Yb and Er ions play a crucial role in this enhancement, converting low-energy infrared photons into higher-energy visible emissions that drive photocatalysis. These findings demonstrate a promising strategy for developing highly efficient and sustainable photocatalysts for wastewater treatment utilizing the abundant yet underexplored infrared region of the solar spectrum.