In situ fabrication of EuF3 nanocrystals/poly (N-isopropylacrylamide)-co-polyacrylic acid nanogels and their thermo- and pH-sensitive performance

• Novel in situ method to fabricate rare earth nanocrystals based fluorescent nanogels.
• Fluorescent nanogels with thermo- and pH-sensitive performance derived from rare earth nanocrystals.
• The stimulus-responsive behavior of the nanogels was studied by PL at various temperatures and pH values.

In this paper, we report a new in situ route to fabricate thermo- and pH-sensitive fluorescent complex nanogels which are based on rare-earth nanocrystals. Firstly, 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 50–100 nm and 200 nm, 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.