Pristine and rare earth ions (Y3+ and La3+) decorated rhombohedral nano CaCO<inf>3</inf>/PEG were extracted from natural dolomite rock using a novel green route biomimetic synthesis. XRD analysis confirmed the crystal phase and doping of Y3+ and La3+ in the CaCO<inf>3</inf>/PEG. The FTIR analysis confirmed the presence of various functional groups in the synthesized nanoparticles. The obtained products exhibited good thermal stability at the temperatures up to 844 °C. The absorption and emission peaks were blue-shifted due to the impact of the doping ion concentration. The surface chemical compositions were analyzed using XPS. The direct and indirect bandgap energies of nCY<inf>1</inf> (0.02 M Y3+: CaCO<inf>3</inf>/PEG) and nCL<inf>1</inf> (0.02 M La3+: CaCO<inf>3</inf>/PEG) were 3.95, 3.27 eV (direct bandgap) and 2.52, 2.09 eV (indirect bandgap) respectively. The measured fluorescence quantum yields of nCY<inf>1</inf> and nCL<inf>1</inf> were 22% and 26%, respectively. FESEM with EDX mapping and HR-TEM with SAED analysis was used to determine the morphology, elemental mapping, and crystalline behavior. The photocatalytic activity of prepared samples were performed against methylene blue under UV irradiation. Based on photocatalytic results, nCL<inf>1</inf> showed extremely high photocatalytic activity (92%). The effects of the scavenging agents were investigated using superoxide radicals, photogenerated holes, electrons, and OH radicals. Hence, the prepared samples could be an effective catalysts for significant environmental issues. This is the first study for preparing Y3+ and La3+ doped CaCO<inf>3</inf>/PEG nanoparticles from natural dolomite rock using a low-cost and nontoxic biomimetic method to get enhanced photodegradation efficiency. © 2023 Elsevier B.V., All rights reserved.