Rapid microwave-enhanced hydrothermal synthesis and shape evolution of uniform NaGdF₄: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-NaGdF4:Ln(3+) (Ln = Yb, Er/Tm/Ho) nanocrystals (NCs) with multicolour upconversion luminescence and paramagnetic properties. It has been found that the uniform β-NaGdF4: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 NaGdF4: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-NaGdF4:Ln(3+) NCs.