New insights into structural and spectroscopic characteristics of Cu2+ doped β-Ca3(PO4)2: Correlation between Cu2+ concentration and material properties

• Site occupancy of Cu 2+ in β-Ca 3 (PO 4 ) 2 is correlated to its concentration. • Cu 2+ occupies both Ca4 and Ca5 sites in β-Ca 3 (PO 4 ) 2 crystal. • Photoluminescence emissions of Cu 2+ doped β-Ca 3 (PO 4 ) 2 vary with Cu 2+ concentration. • Thermodynamic modeling of Cu 2+ doped β-Ca 3 (PO 4 ) 2 is at variance with experiments. Doping β-tricalcium phosphate (β-TCP) with copper (Cu 2+ ) has great potential in various applications due to its rich chemistry. However, the doping characteristics are rarely studied in detail and are yet to be fully understood, creating a gap in the existing knowledge of these multifunctional materials. In this work, a series of Cu 2+ doped β-TCP (Cu x -TCPs) were prepared and comprehensively characterized to investigate the correlation between Cu 2+ doping and the material properties. Also, the synthesis of Cu x -TCPs was modeled using thermodynamic equilibrium calculations to investigate their formation pathways. The calculations predicted a possible inclusion of Cu 2+ in intermediate phosphate phases during the material synthesis, depending on the temperature. The structural analyses revealed lattice shrinkage due to the Cu 2+ doping and that Cu 2+ occupied Ca4 and Ca5 sites in the β-TCP crystal. The vibrational spectroscopy of the Cu x -TCPs showed noticeable deformation of ν 1 band of P O 4 3 - ligand. The ultraviolet–visible absorption analysis revealed a reduction in the band gap energy induced by Cu 2+ doping. Photoluminescence spectroscopy demonstrated an enhanced emission tunability of Cu x -TCPs in the blue and orange/red ranges depending on the Cu 2+ concentration. These findings are a step toward a deeper understanding of the structure–property relationship of Cu 2+ doped β-TCPs and can play a significant role in their multidisciplinary applications