In-situ Fabrication Of EuF₃ Nanocrystals/PNIPAM-co-PAA Nanogels And Study On Their Fluorescence Performance

In recent years, the fabrication of rare earth nanocrystals, even functionalization of rare earth nanocrystals supply a better platform for researchers in biology, fluorescence probes and medical imaging fields and so on. Smart materials have been got attention due to thermo-responsive, especially poly (N-isopropylacrylamide). If combining the different materials advantage, thermo-responsive fluorescent complex materials will get a better application prospect. In the paper, series of thermo-responsive fluorescent and based on fluorescence resonance energy transfer (FRET) novel complex nanogels were in-situ fabricated, and the Hg2+ ions selective behavior was studied. In this work, the main contents are as follows:1. Firstly, the poly (N-isopropylacrylamide)-co-polyacrylic acid (PNIPAM-co-PAA) nanogels are prepared by free radical polymerization method. Then, Eu(NO3)3 solution and NaF solution are added in turn. Finally, the EuF3 nanocrystals/PNIPAM-co-PAA complex nanogels are produced. The structure of the complex nanogels is characterized by Transmission electron microscopy (TEM), Fourier transform infrared (FTIR), Thermogravimetric (TG) and X-ray diffraction (XRD), and their stimulus-responsive performance is investigated by Photoluminescence (PL), Differential scanning calorimeter (DSC) and Ultraviolet-visible spectrum (UV-vis) at various temperatures and pH values. The results show that the sizes of PNIPAM-co-PAA nanogels and EuF3 nanocrystals/PNIPAM-co-PAA complex nanogels are mostly about 50-100nm and 200nm, respectively. The needle-like EuF3 nanocrystals are successfully fabricated and the PL intensity of complex nanogels is significantly affected by either the ambient temperature or pH values.2. Firstly, using EDTA, Er(NO3)3, Yb(NO3)3, Y(NO3)3 and NaF as raw materials, up-conversion NaYF4:Yb3+-Er3+ nanocrystals were synthesized by hydrothermal method. Then, the nanocrystals were decorated with MPS. Finally, novel core-shell nanogels of NaYF4:Yb3+-Er3+ nanocrystals/P(NIPAM-co-RhBHA) based on up-conversion excitation and fluorescence resonance energy transfer (FRET) were fabricated via free radical emulsion polymerization of N-isopropylacrylamide (NIPAM) and rhodamine B derivative (RhBHA) dye monomers. Their structure, stimuli-responsive behaviors were investigated via TEM, FTIR, XRD, DSC, UV-vis and PL in detail. The results suggest that, the sizes of NaYF4:Yb3+-Er3+ nanocrystals are 100-300nm, the thickness of P (NIPAM-co-RhBHA) shell is 12nm. The nanogels can response to multi-stimuli, such as pH, temperature, metal ions, and they can be used as sensitive detector for Hg2+ ions.