Nano CaCO<inf>3</inf> (nC)<inf>,</inf> various polymer mediated nano CaCO<inf>3</inf> and Eu3+ anchored nano CaCO<inf>3</inf>/PEG were synthesized from natural carbonate source (Dolomite) (CaMg(CO<inf>3</inf>)<inf>2</inf>) using a novel, low cost, non-toxic and effective route biomimetic synthesis. The mineralogy, structural, thermal stability, and morphology analysis of the products were assessed through FTIR, XRD, TG-DTA, FE-SEM with EDX mapping, and HR-TEM with SAED. Results show that the prepared samples were in the form of calcite with rhombohedral (25-36 nm) structure. The prepared products exhibit good thermal stability up to 844° C. The products show a spherical and porous like structure. The elemental compositions of the products were confirmed through EDX analysis. All the plane values (observed from SAED) were matched with XRD results. An increase of Eu3+ in CaCO<inf>3</inf> shows that the absorption and emission peaks are blue shifted and the band gap values are red shifted. The measured photoluminescence quantum yield values of 0.02 Eu3+:CaCO<inf>3</inf>/PEG (nCE<inf>1</inf>) and 0.08 Eu3+: CaCO<inf>3</inf>/PEG (nCE<inf>4</inf>) are 21% and 19%, respectively. Finally, the products (nC, nCE<inf>1</inf>, and nCE<inf>4</inf>) were subjected to photodegradation application and results shows that nCE<inf>1</inf> has good photocatalytic activity against methylene blue (87%) for 90 min. © 2023 Elsevier B.V., All rights reserved.