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

Doping β-tricalcium phosphate (β-TCP) with copper (Cu²⁺) 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 Cu²⁺ doped β-TCP (Cu_x-TCPs) were prepared and comprehensively characterized to investigate the correlation between Cu²⁺ 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 Cu²⁺ in intermediate phosphate phases during the material synthesis, depending on the temperature. The structural analyses revealed lattice shrinkage due to the Cu²⁺ doping and that Cu²⁺ occupied Ca4 and Ca5 sites in the β-TCP crystal. The vibrational spectroscopy of the Cu_x-TCPs showed noticeable deformation of ν₁ band of ${PO}_4^{3-}$ ligand. The ultraviolet–visible absorption analysis revealed a reduction in the band gap energy induced by Cu²⁺ doping. Photoluminescence spectroscopy demonstrated an enhanced emission tunability of Cu_x-TCPs in the blue and orange–red regions depending on Cu²⁺ concentration. These findings are a step toward a deeper understanding of the structure–property relationships of Cu²⁺ doped β-TCPs and can play a significant role in their multidisciplinary applications.