We initially reported the synthesis, characterization of structural, optical, morphological, and photocatalytic properties of Ag_1.98Cu_0.02WO₄ solid solution in this work. The results were compared with the same characterizations performed in pure silver tungstate. Both materials exhibited an orthorhombic structure, with a high degree of crystallinity and purity. Although, a small number of copper atoms in the orthorhombic unit cell of Ag_1.98Cu_0.02WO₄ were detected by changes in the X-ray diffraction peak intensity and shift in peak positions corroborates with changes observed in micro-Raman active modes. The decrease in the optical band gap, α-Ag₂WO₄ (3.05 ± 0.03 eV) to α-Ag_1.98Cu_0.02WO₄ (2.93 ± 0.01 eV), determined by diffuse reflectance spectroscopy, confirms the insertion of intermediate levels between valence and conduction bands that could be associated with the Jahn–Teller effect of copper. Field-emission scanning electron microscopy images show several rod-like microcrystals for α-Ag₂WO₄, while there are heterogeneous microcrystals for Ag_1.98Cu_0.02WO₄ solid solution with an inherent polyhedral shape. The highest photocatalytic performance of α-Ag_1.98Cu_0.02WO₄ in the degradation of RhB molecules under visible blue light-emitting device irradiation was achieved at the end of 120 min, therefore 10.61 times faster than pure α-Ag₂WO₄ and 37.77 times than the photolysis experiment. Through the photocatalytic experiments using the scavenger radicals, the contribution of holes (h⁺), singlet oxygen (¹O₂), superoxide radicals (O₂^•–), and hydroxyl radicals (^●OH) were evaluated, where the holes (h⁺), singlet oxygen (¹O₂), and superoxide radicals (O₂^•–) show the main contribution in the photocatalytic degradation of the RhB molecules to colorless organic compounds, carbon dioxide (CO₂), and water (H₂O).