Synthesis of NaYF4:Yb,Er/NaYF4 nanoparticles coated with PAM by in-situ polymerization Original Research Article

Rare earth co-doped upconversion nanoparticles (UCNPs), which can convert a radiation from a longer wavelength to a shorter wavelength, have great potential uses in bio-labeling and imaging. In this work, NaYF4:Yb,Er/NaYF4 UCNPs were coated with poly(acrylic amide) (PAM) by in situ polymerization for the first time. The resulting UCNPs and the PAM coated nanocomposites were characterized by the powder X-ray diffraction (XRD) method, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and upconversion photoluminescence spectroscopy (PL). Effects of reaction temperature, acrylic amide content, and the reaction time on the formed nanocomposites were investigated. The XRD result indicated that the as-prepared UCNPs exhibited a pure hexagonal phase. TEM results displayed that well-dispersed UCNPs having an obvious core–shell structure and a mean size of 110 nm were obtained at 0 °C with 14.0 wt% acrylic amide content (the content percentage in the whole reaction system) within 250 min. Meanwhile, the FT-IR spectra and TGA curves revealed that these NPs were coated successfully with PAM and had a high UC luminescent intensity as from the PL spectra. In addition, the settlement tests revealed that PAM-coated NaYF4 nanocomposites had more favorable dispersion stability than uncoated UCNPs in a distilled water system. These nanocomposites with excellent water-solubility and amino-functionalization could be used for biological detection and bio-imaging.