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

Abstract

Highly biocompatible and efficiently luminescent whiskers of the hydroxyapatite (Ca 10 (PO 4) 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 Eu 3+ : Eu 2+ = 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 fieldemission 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 (5 D 0 → 7 F 2) and ~697 nm (5 D 0 → 7 F 4), 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.

Characterization and Luminescence of Eu3+- and Gd3+-Doped Hydroxyapatite Ca10(PO4)6(OH)2

“…The loss of OH − group for higher T is also feasible to induce a local structural distortion [48], that probably involves the anomalous appearance of the forbidden transition. This feature is unusual and was previously found in similar nano crystalline Ca 10 (PO 4 ) 6 (OH) 2 doped with 3% of Eu 3+ [30], while the hypersensitive 5 D 0 → 7 F 2 transition was otherwise dominant in HA-Eu materials [6,10,13].…”

“…), the 5 D 0 → 7 F 0 transition shows a single band [66], indicating the disorder of Eu 3+ at non-equivalent Ca 2+ sites, i.e., Ca1 (higher symmetry) and Ca2 (lower symmetry). In particular, Eu 3+ may enter preferentially the Ca2 site in order to better optimize the charge balance through the thermal diffusion mechanism occurring in these materials [10,66]. The mechanism can be described according to [64] OH…”

“…Specifically, in biomedical sciences, HA is used in: orthopedics, such as coating for metallic prothesis, bone filler [5] and as composite materials HA/poly (L-lactide) for bone tissue scaffolds [6]; orthodontics, e.g., cements and dental implants [7]; oncology (cancer treatments) [8]; carrier in drug delivery applications [9,10], and so on. In this context, in recent years there has been a growing interest in rare-earth (RE) doped HA materials, due to the excellent luminescence properties of RE, which has induced a strong interest in these materials for applications exploiting light-emission properties [11,12].…”

“…In this context, in recent years there has been a growing interest in rare-earth (RE) doped HA materials, due to the excellent luminescence properties of RE, which has induced a strong interest in these materials for applications exploiting light-emission properties [11,12]. These materials are more suitable than the common fluorescent organic molecules, since their luminescence properties are not affected by the exposure to irradiation [10]. Moreover, incorporation of RE into the HA matrix overcome the risk of toxicity deriving from RE ions in view of biomedical applications [13].…”

Synthesis of Gd+3 doped hydroxyapatite ceramics: optical, thermal and electrical properties

“…It is seen in this study as well that the Gd 3+ ions coupled to this high energy vibration [35]. On the other hand, it is well understood that Gd 3+ may enter preferentially the Ca +2 site in order to better optimize the charge balance through the thermal diffusion mechanism occurring in these materials [5,36]. The mechanism can be written as in the equation 1 and 2 [37].…”