Praseodymium selective fluorescence recognition based on GdPO4: Tb3+ probe via energy transfer from Tb3+ to Pr3+ ions.

A novel strategy is proposed based on the efficient energy transfer from Tb3+ to Pr3+ for the sensitive and selective discrimination of praseodymium ions due to the matched energy levels of 5D4 (Tb3+) and 3P0 (Pr3+). The electron of Tb3+ transfers from the ground state to the excited state under the excitation of ultraviolet light and relaxes to the 5D4 level. In the presence of Pr3+ the electron has no time to return to the ground state, thus it transfers to the 3P0 level of Pr3+ resulting in the quenching of Tb3+ luminescence. In the case of GdPO4: Tb3+ nanowire, its fluorescence intensity at 545 nm linearly decreased when Pr3+ concentration ranged from 1 × 10-7 to 1 × 10-5 M, and the detection limit was 75 nM. To further investigate the sensing mechanism, CePO4: Tb3+, YPO4: Tb3+, and YBO3: Tb3+ nanoparticles were also synthesized for Pr3+ ion detection. For all materials, similar fluorescence quenching by Pr3+ ions occurred, which confirmed the efficient energy transfer from Tb3+ to Pr3+ ions. Utilizing the matched energy levels of 5D4 (Tb3+) and 3P0 (Pr3+), for the first time, we proposed a novel strategy (taking GdPO4: Tb3+ probe as the example) based on the efficient energy transfer from Tb3+ to Pr3+ for the sensitive and selective discrimination of praseodymium ions.

EDTA-assisted phase conversion synthesis of (Gd0.95RE0.05)PO4 nanowires (RE = Eu, Tb) and investigation of photoluminescence.

Hexagonal (Gd0.95RE0.05)PO4·nH2O nanowires ~300 nm in length and ~10 nm in diameter have been converted from (Gd0.95RE0.05)2(OH)5NO3·nH2O nanosheets (RE = Eu, Tb) in the presence of monoammonium phosphate (NH4H2PO4) and ethylene diamine tetraacetic acid (EDTA). They were characterized by X-ray diffraction, thermogravimetry, electron microscopy, and Fourier transform infrared and photoluminescence spectroscopies. It is shown that EDTA played an essential role in the morphology development of the nanowires. The hydrothermal products obtained up to 180 °C are of a pure hexagonal phase, while monoclinic phosphate evolved as an impurity at 200 °C. The nanowires undergo hexagonal→monoclinic phase transformation upon calcination at ≥600 °C to yield a pure monoclinic phase at ~900 °C. The effects of calcination on morphology, excitation/emission, and fluorescence decay kinetics were investigated in detail with (Gd0.95Eu0.05)PO4 as example. The abnormally strong 5D0→7F4 electric dipole Eu3+ emission in the hexagonal phosphates was ascribed to site distortion. The process of energy migration was also discussed for the optically active Gd3+ and Eu3+/Tb3+ ions.

Phase evolution, mechanical properties and MRI contrast behavior of GdPO4 doped hydroxyapatite for dental applications.

Ca10(PO4)6(OH)2 doped with GdPO4 (HA-GP) was synthesized by a sol-gel technique, and its phase composition depended on the GdPO4 content. At low doping levels, the phase structure was composed of hydroxyapatite and some Ca3(PO4)2, and the content of the latter decreased with the doping content; when the doping content reached to 15 mol%, however, the Ca3(PO4)2 amount revealed a significant increase, and GdPO4 turned to be precipitated. With the addition of GdPO4, the microstructure of HA-GP pellets became dense, and the grain size decreased. GdPO4 doping enhanced the hardness of HA-GP due to a grain size effect. With increasing the doping content, the toughness increased initially followed by a decrease, and 7.5 mol% doping (HA-GP7.5) led to the highest toughness. Magnetization tests revealed that GdPO4 had paramagnetic behavior, which made it suitable for magnetic resonance imaging (MRI) contrast agent. The MRI contrast behavior of HA-GP7.5 was investigated. With the increase of the concentration, the T1 weighted MR image revealed enhanced brightness, while the brightness of T2 weighted MR images reduced gradually. Considering the phase structure, mechanical properties, and MRI contrast behavior, HA-GP7.5 might have a potential to be used in clinical medicine.