Influence of Morphology on Luminescent and Structural Properties of Eu3+-Doped Hydroxyapatite Powders Sintered by Spark Plasma Sintering.

This study investigates the microstructure, phase stability, hardness, and luminescent properties of europium-doped hydroxyapatite (HA: Eu) powders synthesized via the hydrothermal method and sintered by spark plasma sintering (SPS) at 900 °C. The morphology of the powders was controlled using different glycerol concentrations, yielding plate-like (L/D = 2.09), rod-like (L/D = 1.61), and elongated spherical morphologies. X-ray diffraction confirmed the retention of the hexagonal HA phase after sintering, with crystallite sizes ranging from 47.5 nm to 75.5 nm. The densification of sintered samples reached up to 96.45%, with HA3S (plate-like morphology) achieving the highest value. Photoluminescence analysis revealed characteristic emission peaks of Eu³⁺ at 574-631 nm under 394 nm excitation, with a migration fraction from Ca²⁺(I) to Ca²⁺(II) of 67% for the smallest particle size. Mechanical testing showed that the microhardness varied significantly with porosity and morphology, with HA3S reaching a maximum hardness of 5.67 GPa, compared to 2.1 GPa for HA1S. These results highlight the importance of morphological control in tailoring the optical and mechanical properties of Eu³⁺-doped HA for biomedical applications.