A Method to Improve the Up-Conversion Fluorescence of Polymer Modified NaYF₄:Yb,Er(Tm) Nanocomposites

Weina Cui, Siyu Ni, Shunan Shan, Xingping Zhou

College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, Shanghai, China.
College of Life and Environment, Shanghai Normal University, Shanghai, China.

DOI: 10.4236/wjnse.2012.22007                

Abstract

The modification of NaYF₄: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, NaYF₄: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 NaYF₄:Yb,Er(Tm) in tetrahydrofuran (THF) was treated with excess PAA. The PAA modified NaYF₄: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, NaYF₄:Yb,Er(Tm)/NaYF₄ nanoparticles were synthesized before PAA modification to avoid the optical intensity decaying. The result of fluorescence test proved that the water soluble NaYF₄:Yb,Er(Tm)/NaYF₄/PAA nanocomposites had a sound up-conversion property compared with that of NaYF₄: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.

Keywords

Doping Ratio; Fluorescence; Ligand Exchange; Polyacrylic Acid; Sodium Yttrium Fluoride;Surface Modification

Conflicts of Interest

The authors declare no conflicts of interest.

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