Rapid microwave-enhanced hydrothermal synthesis and shape evolution of uniform NaGdF 4:Yb, Er (Tm/Ho) nanocrystals with upconversion and paramagnetic properties

Abstract

An efficient microwave-enhanced hydrothermal synthesis strategy was developed for the rapid synthesis of β-NaGdF 4:Ln 3+ (Ln=Yb, Er/Tm/Ho) nanocrystals (NCs) with multicolour upconversion luminescence and paramagnetic properties. It has been found that the uniform β-NaGdF 4:Ln 3+ NCs could be rapidly formed within a few minutes at 160°C and the shape of the NCs can be manipulated from uniform rod-like to spherical just by tuning the initial reactants concentration. In comparison to conventional hydrothermal routes, a burst homogeneous nucleation and higher growth rate as well as enhanced dimensional homogeneity of the NaGdF 4:Ln 3+ was achieved in microwave synthesis. A microwave-heating-based classical crystallization mode and surfactant-assisted anisotropic growth mechanism were proposed for the formation of β-NaGdF 4:Ln 3+ NCs. © 2012 IOP Publishing Ltd.