A Method to Improve the Up-Conversion Fluorescence of Polymer Modified NaYF<sub>4</sub>:Yb,Er(Tm) Nanocomposites
- 1 College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, Shanghai, China
- 2 College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, Shanghai, China
- 3 College of Life and Environment, Shanghai Normal University, Shanghai, China
- 4 College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, Shanghai, China
Abstract
The modification of NaYF 4 :Yb,Er(Tm) nanoparticles synthesized in the presence of an ionic surfactant is critical to their application in biological fields for better solubility and biocompatibility. In this work, NaYF 4 :Yb,Er(Tm) was transformed from insoluble, inactive to hydrophilic, biocompatible via ligand exchange modification with polyacrylic acid (PAA). Ligand exchange was carried out at room temperature when a colloidal solution of NaYF 4 :Yb,Er(Tm) in tetrahydrofuran (THF) was treated with excess PAA. The PAA modified NaYF 4 :Yb,Er(Tm) nanoparticles got better surface properties but with declined inner up-conversion fluorescence. Generally, coating an analogous layer of material outside the core nanoparticles can improve the optical properties of the core. Accordingly, NaYF 4 :Yb,Er(Tm)/NaYF 4 nanoparticles were synthesized before PAA modification to avoid the optical intensity decaying. The result of fluorescence test proved that the water soluble NaYF 4 :Yb,Er(Tm)/NaYF 4 /PAA nanocomposites had a sound up-conversion property compared with that of NaYF 4 :Yb,Er(Tm)/PAA. Furthermore, the up-conversion fluorescence property of the nanocomposite varied with the doping ratio of Er(Tm) to Yb and the possible mechanism for this change was also discussed.
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