Preparation Of EuF₃/PNIPAm Complex Hydrogel And Study On Their Fluorescent Performance

Rare earth nanocrystals and poly N-isopropyl acrylamide (PNIPAm) basedcomplex hydrogel is a family of novel smart materials, which combines thefeatures of rare earth such as unique optical, electrical, magnetic properties, andcharacteristics of environment sensitivity. Influeced by the variation of ambienttemperatures, the gels matrix will present abrupt phase’s change at their Lowercritical solution temperatures (LCST), and the fluorescent emission of thecomplex gels will change correspondingly. Hence, these complex fluorescentgels will play an important role in developing sensoring materials, for example,sonsors for temperature, drug and/or biological molecules. In the present paper,rare earth nanocrystals such as, EuF3, NaYF4, NaYF4：Eu3+nanocrystals wereprepared by LSS(liquid–solid–solution) method and a series of rare earthnanocrystals/PNIPAm complex hydrogels was synthesised via radicalpolymerization. The main works are focused on the thermo-sensitive fluorescentproperties of the complex gels and their mechanism.1. EuF3and NaYF4nanocrystals were prepared respectively, and they wereused to prepare a series of novel ternary complex hydrogels of EuF3-NaYF4nanocrystals/PNIPAm. The structure and fluorescent properties of nanocrystalsand the complex hydrogels were characterized by Differential ScanningCalorimeter(DSC), Photoluminescence(PL), Fourier transform infrared (FT-IR),X-ray diffraction (XRD) and High-Resolution Transmission electronmicroscopy(HRTEM). And the thermosensitive fluorescent behavior of thecomplex hydrogels was investigated and the mechanism was discussed in detail.The results suggest that, in the PNIPAm hydrogel matrix, energy can betransferred between the bulk doped EuF3nanocrystals and NaYF4nanocrystals.Either the relative content of two kinds of nanocrystals or the ambienttemperature plays important roles in the thermosensitive fluorescent behavior ofthe complex hydrogels.2. NaYF4:Eu3+nanocrystals were prepared by LSS strategy. Then they weretreated by CCl4to obtain reactive NaYF4:Eu3+nanocrystals. Then ATRP methodwas used to prepare a ternary complex hydrogels of NaYF4:Eu3+-PNIPAm-co-NBDAE. The structure and fluorescent properties of nanocrystalsand the complex hydrogels were characterized by DSC, PL, FT-IR, XRD and HRTEM. And the thermosensitive fluorescent behavior of the hydrogels wasstudied and the mechanism was discussed. The results show that thefluorescence energy transfer (FRET) was existed between NaYF4:Eu3+nanocrystals and NBDAE, and the FRET efficiency enhanced with the increaseof temperature.3. EuF3nanocrystals were prepared by LSS method, and they were used toprepare the thermosensitive complex hydrogels of EuF3/PNIPAm. Then the BSAadsorption property of complex hydrogels was studied. The structure andfluorescent properties of nanocrystals and the complex hydrogels werecharacterized by PL, DSC, and FT-IR. The results show that the content ofadsorbed BSA increases with increasing either temperature or time.