Spatial Arrangement of Porphyrin-Eu(III) Ions on Apatite Nanoparticles

Eu³⁺-doped hydroxyapatite nanoparticles were functionalized with anionic porphyrin to investigate their spatial arrangement on the surfaces. The porphyrin selectively coordinates to Eu³⁺ rather than Ca²⁺ sites. Photoluminescence changes in both the porphyrin and Eu³⁺ indicated that the coordination environment around Eu³⁺ evolved with increasing porphyrin loading. The photoluminescence property variations by the Eu³⁺ suggested a transition from mono- to multicoordination, resulting in the symmetric arrangement of multiple molecules around Eu³⁺.