Surfactants Assisted Hydrothermal Synthesis of NaYF4 co-doped Yb3+/Er3+ Up-conversion Nanoparticles

Abstract

In the past few years there is a great interest for synthesis of the surface modified upconversion nanoparticles that can be used for biomedical application such as bio-detection, fluorescene imaging and drug delivery. Thanks to their enhanced tissue penetration depth, improved stability against photo-bleaching and low cytotoxicity Ln-doped fluorides have been recognized as novel near-infrared fluorophores. Among them, NaYF4 is considered to be one of the most efficient low phonon energy host for Ln-ions doping, particularly its hexagonal form which poses multisite character of the crystal lattice. In this work NaYF4 nanoparticles co-doped with Yb3+ and Er3+ were synthesized using the hydrothermal method at 200 ºC (3h) in the presence of polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG), used as surfactants and structure directing agents also. Obtained particles were analyzed by X-ray powder diffractometry (XRPD), Furrier transform infrared spectroscopy (FTIR) and scanning/transmission electron microscopy (SEM/TEM). It was shown that addition of PVP enhance the crystallization of hexagonal NaYF4:Yb3+, Er3+ phase which provide more intense green emission CIE (0.31, 0.66), assigned to the Er3+(2H11/2, 4S3/2) → 4I15/2 electronic transitions, after been excited with infrared light (λ=978 nm).