Changfu Xu

High uniformity and monodispersity of sodium rare-earth fluoride nanocrystals: controllable synthesis, shape evolution and optical properties

Highly uniform and monodispersed pure hexagonal phase NaReF4 (Re = Y, Pr–Nd, and Sm–Yb) nanocrystals with well-defined morphologies, including pills, rods, spheres, tubes, and plates, were systematically synthesized by a facile solution-based hydrothermal method using oleic acid as a stabilizing agent. Crystal phase, shape and size can be tuned readily by simply adjusting the molar ratio of F/Re and reaction temperature. Detailed experimental studies revealed that NaReF4 hosts strongly tend to form hexagonal phase nanocrystals with increasing rare earth ion radius. Based on the studies on crystal phase control and shape evolution of NaReF4 nanocrystals, the whole growth mechanism of nanocrystals can be concluded as a kinetic and thermodynamic growth process. Simultaneously, highly efficient up-conversion luminescence under 980 nm excitation was realized, such as eye-visible red, green, and blue up-conversion luminescence generated from NaYbF4 host doped with Er3+, Ho3+, and Tm3+, respectively. Due to their unique up-conversion luminescence, the highly uniform and monodispersed nanocrystals can be applied for biolabels, colour displays, light-emitting diodes, and solid-state lasers.

Modifying crystal phase, shape, size, optical and magnetic properties of monodispersed multifunctional NaYbF4 nanocrystals through lanthanide doping

In this paper, a simple lanthanide (Ln) doping route for modifying the crystal structure including crystal phase, shape, size and physics properties such as up conversion (UC) and magnetic properties of monodisperse multifunctional NaYbF4 nanocrystals is demonstrated. The results revealed that the crystal phase transformation from cubic to hexagonal phase, shape evolution from one-dimensional (rods) to zero-dimensional (nanoparticle) and size transition from microscale to nanoscale can be readily tuned. Moreover, these nanocrystals doped with different Gd3+ concentrations exhibit multi-functionality, including tunable UC emissions colours and paramagnetic properties, which making them potentially applicable in the biological field as biolabels, bioseparation, magnetic resonance imaging (MRI), and optical-magnetic dual modal nanoprobes in biomedical imaging. It is also expected that the doping-induced structure and physical properties transformation can be applied to other NaLnF4 nanocrystals.

Tri-color upconversion luminescence of Rare earth doped BaTiO 3 nanocrystals and lowered color separation

Upconversion tri-color luminescence of Er(3+)/Tm(3+)/Yb(3+) doped BaTiO3 nanocrystals is observed under the excitation of a 980 nm laser diode. Especially, Er(3+) emission has a considerable contribution to the blue portion of the UC spectra, different from the ever-reported results, in which blue emission originates only from Tm(3+). This realization is beneficial to lower the color separation between blue and green (or red) emissions, in fluorescent labeling. The analysis of excitation power dependence and decay time revealed that blue emission of Er(3+) ion is induced by a dual energy transfer upconversion, while Tm(3+) plays a role of both emitter and activator.

White upconversion of rare-earth doped ZnO nanocrystals and its dependence on size of crystal particles and content of Yb3+ and Tm3+

Rare earth (RE) doped ZnO nanocrystals were synthesized by chemical combustion method. Bright white upconversion (UC) luminescence with the CIE coordinates close to (0.33, 0.33) was obtained in Er+Tm+Yb tridoped ZnO nanocrystals under the excitation of a cost-effective 980 nm single-wavelength laser diode. The overall and relative UC luminescence intensities of RE doped ZnO nanocrystals were found to be depended highly on the diameter of crystal particles and the concentration of Yb3+ and Tm3+, for which the involved mechanisms were demonstrated. The investigation based on UC spectra, simplified energy level diagram, and excitation power dependence indicated that the remarkable enhancement of the green emission of the RE tridoped sample was due to a dual sensitization of Er3+ by Yb3+ and Tm3+ ions. The RE tridoped ZnO nanocrystals with the CIE coordinates close to (0.33, 0.33) are potentially suitable for the widely realistic application as the multicolor fluorescent labels, due to a fact that they could ...

Lanthanide doping-facilitated growth of ultrasmall monodisperse Ba2LaF7 nanocrystals with excellent photoluminescence

Lanthanide doping not only works as sensitizer and activator, but also plays an important role to facilitate the growth of nanocrystal and to control the size, shape, and property of nanocrystals. Here, reported was the synthesis of monodisperse Ba(2)LaF(7) nanocrystals with the size of sub-10nm through a solvothermal method. We found the dopants of Ho(3+), Er(3+), or Yb(3+) facilitated the growth of Ba(2)LaF(7) nanocrystals obviously to a certain size within a shorter reaction time. Similar phenomenon can also be observed in the synthesis of LaF(3) nanocrystals. We find that Ln(3+) (e.g., Ho(3+), Er(3+), or Yb(3+)) with smaller radius can reduce the nucleation energy and lead to heterogeneous nucleation, which favors the growth of Ba(2)LaF(7) nanocrystals obviously. In addition, intense upconversion emission can be observed from Ln(3+)-doped Ba(2)LaF(7) nanocrystals under the 980 nm laser excitation, providing great potential application in biological imaging. Especially, Ba(2)LaF(7):Yb/Er (20/1 mol%) nanocrystals present more intense upconversion emission than α-NaYF(4):Yb/Er (20/1 mol%) nanocrystals under the same conditions.

Single-narrow-band red upconversion fluorescence of ZnO nanocrystals codoped with Er and Yb and its achieving mechanism

ZnO nanocrystals doped with Er3+ and Yb3+ ions were synthesized by the chemical-combustion process. The single-narrow-band red fluorescence (centered at 662 nm) in ZnO:Er, Yb was observed under 115 mW excitation of a 980 nm laser diode. The full width at half maximum of the red emission band is equal to 30 nm, which is the narrowest emission band ever reported in Er3+ doped systems. This narrower emission band in ZnO:Er, Yb nanocrystal is beneficial for improving the precision and sensitivity of the indicators in fluorescent label detection. The mechanisms resulting in the single-narrow emission band were analyzed by combining X-ray diffraction, Raman spectra, fluorescence spectra, and a simple model.ZnO nanocrystals doped with Er3+ and Yb3+ ions were synthesized by the chemical-combustion process. The single-narrow-band red fluorescence (centered at 662 nm) in ZnO:Er, Yb was observed under 115 mW excitation of a 980 nm laser diode. The full width at half maximum of the red emission band is equal to 30 nm, which is the narrowest emission band ever reported in Er3+ doped systems. This narrower emission band in ZnO:Er, Yb nanocrystal is beneficial for improving the precision and sensitivity of the indicators in fluorescent label detection. The mechanisms resulting in the single-narrow emission band were analyzed by combining X-ray diffraction, Raman spectra, fluorescence spectra, and a simple model.

Upconversion emission and paramagnetism of colloid Ba2ErF7 and Ba2ErF7:Yb3+ nanocrystals synthesized with solvothermal method

Ultrasmall near-monodisperse Ba2ErF7 nanocrystals with average crystal size 9.6 nm were synthesized with solvothermal method. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) assays reveal that the as-synthesized Ba2ErF7 nanocrystals are of the cubic structure with the cell parameter of 5.943 Å, instead of the reported orthorhombic and tetragonal structure. Two emission bands originated from 2H11/2/4H3/2 → 4I15/2 and 4F9/2 → 4I15/2 of Er3+ can be observed under a 980 nm laser excitation. The magnetic mass susceptibility of the as-synthesized Ba2ErF7 nanocrystals reaches 4.293×10−5 emu g−1 Oe−1.