Jianxiong Xu

Synthesis of Lanthanide-Ion-Doped NaYF4 RGB Up-Conversion Nanoparticles for Anti-Counterfeiting Application

Well-defined and mono-dispersed lanthanide-ion-doped NaYF4 up-conversion nanoparticles (UCNPs) were synthesized via thermal decomposition using lanthanide oleate as the precursor. By rational selecting the dopant pairs of the doped lanthanide ions (Y3+, Yb3+, Er3+ and Tm3+) with accurate molar ratios, three-primary-color (RGB) UCNPs which exhibited green (UCNPs-G), blue (UCNPs-B) and red (UCNPs-R) fluorescence, respectively, were prepared. The X-ray diffraction (XRD) patterns showed that the three UCNPs were purely hexagonal-phase NaYF4 crystals. Transmission electron microscopy (TEM) images revealed that the synthesized UCNPs exhibited well-defined nanosphere morphology with uniform size distribution. The average diameters were 23.95±3.35 nm for UCNPs-G, 20.63±2.59 nm for UCNPs-B, and 19.24±2.37 nm for UCNPs-R, respectively. After surface modification employing polyacrylic acid (PAA) as modifier, the obtained UCNPs were converted to be hydrophilic, which can be used as fillers to construct luminescent polymer films and luminescent ink in anti-counterfeiting application.

Hydrothermal Synthesis of PAA-Coated NaYF4:Yb3+, Er3+ Nanophosphors with Predicted Morphology, Phase and Enhanced Upconversion Luminescence Properties

In this study, well-defined PAA-coated NaYF4:Yb3+, Er3+ nanophosphors were synthesized via a poly(acrylic acid) (PAA) mediated hydrothermal process. The rational control of initial reaction conditions, such as hydrothermal temperature, pH value of precursor-solution, added amount of PAA, and molecular weight of PAA ligand, resulted in upconversion of NaYF4:Yb3+, Er3+ phosphors with varying crystal phases (α and β) and morphologies (e.g., nanosphere, submicrorod, microrod, microtube, and microprism). By assessing the upconversion luminescent properties of the synthesized NaYF4:Yb3+, Er3+ phosphors upon excitation by 980 nm infrared light, it was demonstrated that the β-phase NaYF4:Yb3+, Er3+ phosphors generally presented stronger upconversion luminescent than α-phase NaYF4:Yb3+, Er3+ phosphors and orthorhombic phase of YF3:Yb3+, Er3+ sample. Additionally, the β-phase NaYF4:Yb3+, Er3+ phosphors with hollow microtube morphology presented higher upconversion luminescent intensity than phosphors of other morphologies. This may be due to microtubes having larger surface area (inner and outer surfaces), which promoted the absorption efficiency under similar excitation conditions, therefore generating higher luminescent intensity. Findings form this study suggest for precisely controlled growth of other complex rare earth fluoride compounds and provide a reference for exploration of component-, phase- and morphology-dependent upconversion luminescence properties.