Up-conversion nanoparticles (UCNPs), which can convert a radiation from a longer wavelength to a shorter wavelength, have great potential uses as bio-labels in biological detection. However, these NPs usually cannot be used directly unless their surfaces are further modified. In this
paper, NaYF4:Yb, Er nanoparticles (NPs) were coated with poly(acrylic acid) (PAA) by in situ polymerization for the first time. Accordingly, NaYF4:Yb, Er/NaYF4 NPs were synthesized before PAA coating to avoid the decay of optical intensity. The resulting
UCNPs were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and up-conversion photoluminescence spectrometry. The XRD results indicated that the resultant UCNPs exhibited a pure
hexagonal phase. The FT-IR spectra and TGA curves revealed that these NPs were coated successfully with PAA. Meanwhile, the TEM results showed that well-dispersed UCNPs with the best morphology and an average size of about 90 nm were obtained with 8.0 wt% acrylic acid content (the content
percentage in the whole reaction system) at 0 °C within 130 min. Fluorescence tests showed that the UCNPs had a strong UC fluorescence intensity. Settlement tests revealed that PAA-coated NaYF4 UCNPs had more favorable dispersion stability than uncoated UCNPs in an aqueous system.
These functionalized nanocomposites could be used for further bio-conjugation.
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