Synthesis of Luminescent Eu(III)-Doped Octacalcium Phosphate Particles Hybridized with Succinate Ions and Their Reactive Behavior in Simulated Body Fluid

We successfully synthesized the photofunctionalized octacalcium phosphate (OCP) with layered structures and high biosafety. Specifically, two systems of europium­(III) ion (Eu3+)-doped OCP particles (OCP:Eu) and succinate (Suc)-modified OCP:Eu particles (Suc-OCP:Eu) were synthesized by substituting an Eu3+ ion with a Ca2+ ion of OCP while maintaining the layered structures. The OCP:Eu and Suc-OCP:Eu (crystal shape sizes: ca. 0.4–1.0 μm) exhibited the strong luminescence based on the f–f transition of the Eu3+ ion, and the luminescence intensity and quantum efficiency increased with increasing the initial Eu molar concentration to Ca+Eu up to 10 mol %, indicating the suppression of the concentration quenching by the layered structures. The intensity and efficiency of Suc-OCP:Eu were about 1.3 times as high as the OCP:Eu, indicating that the hybridization with Suc ions leads to the enhancement of the luminescent properties. The sustained release of the Suc ion from Suc-OCP:Eu in simulated body fluid (SBF) was achieved for more than 168 h, and the release rates at the immersion time of 168 h were 85, 60, and 20% for the Suc-OCP:Eu at the initial molar concentrations of Eu to Ca+Eu of 0, 5, and 10 mol %, respectively. Moreover, the intensity, efficiency, and layer structure of Suc-OCP:Eu were maintained by the immersion time of 168 h. Thus, the effect of the hybridization with Suc ions on the luminescence properties of the Eu3+ ion, and that of the doping on the release of the Suc ion in SBF was clarified. We achieved the synergistic functions of both photofunctions and organic molecules in the layered structure of the biocompatible OCP, and the sustained release of organic molecules in biological solution.