Synthesis of Eu‐doped hydroxyapatite whiskers and fabrication of phosphor layer via electrophoretic deposition process

Abstract

ABSTRACTHighly biocompatible and efficiently luminescent whiskers of the hydroxyapatite (Ca10(PO4)6(OH)2, HAp) doped with various concentrations (0‐5 at.%) of europium were prepared by hydrothermal synthesis and the Eu‐doped Hap‐coating layers onto the surface of titanium substrate were fabricated by the electrophoretic deposition (EPD) process for fluorescent probe application. The maximum doping concentration of Eu accommodating into the host lattice of HAp was detected as ~1.5 at.% and all the hydrothermally synthesized Eu‐doped HAp whiskers were found to have high crystallinity and orientation growth along the c‐axis by X‐ray diffraction (XRD) identification. The valence of the doped Eu was identified as trivalent and divalent coexistence at a concentration percentage of Eu3+: Eu2+ = 78%: 22% by X‐ray photoelectron spectroscopy (XPS) spectra. The replacement site of the doped Eu ions in the crystal structure of HAp host was clarified by Rietveld refinement. The whisker morphology of the hydrothermally synthesized particle was demonstrated by field‐emission scanning electron microscopy (FE‐SEM) observation and their component elements were analyzed by energy dispersive X‐ray (EDX) mapping. The photoluminescence (PL) emissions of the Eu‐doped HAp whiskers and fabricated their coating layers were both revealed mainly at ~615 nm (5D0 → 7F2) and ~697 nm (5D0 → 7F4), which is a wavelength that easily transmitting through living system for biological imaging. The PL emission are falling in the region of reddish orange and belonging to color temperature below 1500 K. Decay time and internal and external quantum efficiencies (QEs) were also measured to reveal them depending on the doping concentration of Eu. The hydrothermally prepared Eu‐doped HAp whiskers would be aimed at biomedical application, due to their promising fluorescent function of probe for in vivo imaging in medical diagnose by utilizing the superior biocompatibility of the HAp host and highly efficient luminescent property of the Eu activator.