One-pot Preparation And Thermosensitive Fluorescent Behavior Of Rare Earth Fluoride Nanocrystals Composite Nanogels

As the representative of thermosensitive hydrogel， polyisopropyl acrylamide(PNIPAM) is a typical kind of environmental sensitive material. Recently,functionalized nanogels have been drawing people’s attention increasingly due to itspotential applications in drug separation, biological engineering, chemical sensing andshape memory and so on. The thermosensitive fluorescent hydrogel compositenanomaterials are gradually becoming a hot topic. By combining fluorescentnanomaterials with thermosensitive hydrogels, the thermosensitive fluorescentfunctional hydrogels can be easily prepared. Therefore，taking adventage of the uniquefluorescent properties of rare earth nanocrystals, to synthesize novel thermosensitivefluorescent hydrogel is very significant. In this work, the main contents are as follows:1. Firstly, using cysteamine, Er(NO3)3, Yb(NO3)3, Y(NO3)3and NH4F as rawmaterials, active YF3:Yb3+-Er3+nanocrystals with-NH2groups were synthesized byhydrothermal method. After that, in the present of the as-prepared active YF3:Yb3+-Er3+nanocrystals, N-Isopropyl acrylamide (NIPAM) and N, N’-methylenebisacrylamide(BIS) were initiated by K2S2O8. Finally, thermosensitive fluorescentnanogels of YF3:Yb3+-Er3+/PNIPAm-co-PAA were fabricated by free radicalpolymerization and in-situ coupling reactionsof1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) andN-Hydroxysuccinimide (NHS). The microstructure and performance of the as-preparedYF3:Yb3+-Er3+nanocrystals and the complex nanogels were investigated by DifferentialScanning Calorimeter (DSC), Photoluminescence (PL), Fourier transform infrared(FTIR), X-ray diffraction (XRD) and High-Resolution Transmission electronmicroscopy (HRTEM). As the evidence from the HRTEM images, active YF3:Yb3+-Er3+nanocrystals show well monodispersity with their size of about6-10nm, and thecomplex nanogels are polydisperse ones with their size of about100-300nm. Theresults of PL spectra at various temperatures suggest that, the active YF3:Yb3+-Er3+nanocrystal present weak double emitting peaks around483nm and496nm, which areresulted from the energy level splitting of4F7/2â†'4I15/2transition of Er3+. As for thecomplex nanogels, the phenomenon of energy level splitting of Er3+is different fromthat of the nanocrystals, with increasing ambient temperatures, double emitting peaksaround483nm and496nm couple into an emitting peak around489nm gradually, andtheir intensity decreases correspondingly. 2. Secondly, we report a novel solution route to obtain rare earth nanotubes. Firstly,the complex of Eu(NO3)3/cysteamine (Eu-Complex) was used as the precursor, thennanotubes of EuF3were fabricated from the precursor and NaF. After that,thermosensitive EuF3nanotubes/PNIPAm nanogels were prepared by decoration ofacrylic acid (AA) and free radical polymerization. In order to investigate the mechanismto produce the nanotubes, the morphology structures of samples at different reactionstages were studied via TEM, and the formation mechanism of nanotubes is proposed.The chemical composition was confirmed by FTIR, XRD and XPS. The opticalproperty of the as-prepared nanotubes and the nanogels was investigated in detail by PL.The results suggest that the nanogels present different fluorescence behavior from theirbulk counterparts.3. Finally, erbium nitrate, methyl methacrylate and phenanthroline were reacted tosynthesize Er(MAA)3-Phen. After that, by co-polymerizing the rare earth complexesand NIPAM monomers, a novel Poly (Er(MAA)3-Phen-NIPAM) nanogel was prepared.The products were investigated by Differential Scanning Calorimeter (DSC),Photoluminescence (PL), Fourier transform infrared (FTIR) and Transmission electronmicroscopy (TEM). Moreover, the PL of new rare earth complexes and nanogels wasstudied and explored in detail. The results suggest that the PL intensity of nanogelscould be affected by the temperatures, different solvents and metal ions.