关键词: YF₃：Yb³⁺-Er³⁺, 纳米晶, PNIPAm-co-PAA, 温敏性, 纳凝胶, 荧光强度

Rare-earth nanocrystals are a family of important nanomaterials due to their unique optical and electronic properties, and they are paid more attention for their applications in the areas of solar energy system, molecular imaging, optoelectronics and catalysis fields. The incorporation of rare-earth nanocrystals into smart gels, which combines the PL features of rare-earth nanocrystals with the reversible and stimuli-responsive properties of smart gels, will provide a new generation of fluorescence markers for practical application. In this paper, we report a one-pot method to prepare thermosensitive fluorescent nanogels from rare earth nanocrystals and PNIPAm-co-PAA nanogels. Firstly, using cysteamine, Er(NO₃)₃, Yb(NO₃)₃, Y(NO₃)₃ and NH₄F as raw materials, active YF₃:Yb³⁺-Er³⁺ nanocrystals with-NH₂ groups were synthesized by hydrothermal method. After that, in the present of the as-prepared active YF₃:Yb³⁺-Er³⁺ nanocrystals, N-isopropyl acrylamide (NIPAm) and N,N'-methylene bisacrylamide (BIS) were initiated by K₂S₂O₈. Finally, thermosensitive fluorescent nanogels of YF₃:Yb³⁺-Er³⁺/PNIPAm-co-PAA were fabricated by free radical polymerization and in-situ coupling reactions of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS). The microstructure and performance of the as-prepared YF₃:Yb³⁺-Er³⁺ nanocrystals and the complex nanogels were investigated by differential scanning calorimeter (DSC), photoluminescence (PL), Fourier transform infrared (FTIR), X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). As the evidence from the HRTEM images, active YF₃:Yb³⁺-Er³⁺ nanocrystals show well monodispersity with their size of about 6～10 nm, and the complex nanogels are polydisperse ones with their size of about 100～300 nm. The results of PL spectra at various temperatures suggest that, the active YF₃: Yb³⁺-Er³⁺ nanocrystal present weak double emitting peaks around 483 and 496 nm, which are resulted from the energy level splitting of ⁴F_7/2→⁴I_15/2 transition of Er³⁺. As for the complex nanogels, the phenomenon of energy level splitting of Er³⁺ is different from that of the nanocrystals, with increasing ambient temperatures, double emitting peaks around 483 and 496 nm couple into an emitting peak around 489 nm gradually, and their intensity decreases correspondingly.

Key words: YF₃:Yb³⁺-Er³⁺nanocrystals, PNIPAm-co-PAA, thermosensitive, nanogel, PL intensity