Microwave-assisted synthesis and up–down conversion luminescent properties of multicolor hydrophilic LaF3:Ln3+ nanocrystals

Abstract

Monodisperse water-soluble LaF₃:Ln³⁺ nanocrystals (NCs) have been successfully fabricated via a fast, facile and environmentally-friendly microwave-assisted modified polyol process with polyvinylpyrrolidone (PVP) as an amphiphilic surfactant. The obtained NCs can be well dispersed in hydrophilic solutions with small sizes in the range of 9–12 nm. The LaF₃:Ln³⁺ NCs (Ln = Eu, Nd, Ce, Tb, Yb, Er, Yb, Ho and Yb, Tm) have the unique feature of up–down conversion from visible to NIR emission owing to the ladder-like arranged energy levels of Ln³⁺ and in particular, the high efficiency upconversion of the two-photon, obtained from excitation by a continuous 980 nm laser. This investigation focuses on both the up and down conversion fluorescence properties of water-soluble monodisperse crystalline LaF₃:Ln³⁺ NCs in such a small size. Furthermore, the three-dimensional PDMS rod-like fluorescence displays and a silica surface modification by a core/shell structure on the obtained NCs can improve the biocompatibility, indicating potential applications in optical 3D devices and as bio-probes.