We report on the structure and properties of novel Sr₂Bi₂O₅/SrCO₃ and Sr₃Bi₂O₆/SrCO₃ heterostructures with SrCO₃ content varying from 10 wt% to 90 wt%. Formation of the heterostructures is succeeded via sintering technique and according to XRD, SEM, and EDX studies has resulted in highly crystalline materials with well-defined carbonate-bismuthate interfaces. In the reaction of photodegradation of phenol in aqueous solution the heterostructures demonstrated photocatalytic activity exceeding that of TiO₂. It is demonstrated that their photocatalytic action is due to the presence of type II semiconductor heterojunctions. The content of SrCO₃ ensuring utmost photocatalytic activity is explained based on numerical modeling of the heterostructures’ formation using ‘Unity’ development platform. In addition, the heterostructures show photoluminescence. Its mechanism proposed here implies permeability of the materials’ heterojunctions to electrons. This work describes new materials that can be used for photodegradation of organic pollutants. Besides, it extends available principles of design of photocatalytically active heterostructures.