Hierarchical bundles structure of β-NaLuF4: facile synthesis, shape evolution, and luminescent properties

Abstract

Uniform β-NaLuF₄ nanorod bundles have been prepared through a facile two-step chemical conversion route without using any surfactants or capping reagents. During the process, lutetium precursors with square morphology were first prepared by a urea-assisted precipitation process, which then grew into the β-NaLuF₄ crystals under a mild hydrothermal condition. Different experimental parameters were examined to investigate the growth mechanisms of the lutetium precursors and the NaLuF₄ crystals. It is found that uniform hexagonal NaLuF₄ nanorod bundles can be obtained via a mild hydrothermal process of 180 °C for 24 h when using 0.5 g NaF and the lutetium precursors prepared with 0.18 g urea. Moreover, the down-conversion (DC) and up-conversion (UC) luminescent properties of NaLuF₄ were also investigated through doping different rare earth ions (Eu³⁺, Tb³⁺, Ce³⁺/Tb³⁺, Yb³⁺/Er³⁺, and Yb³⁺/Ho³⁺). It has been shown that the existence of Ce³⁺ ion can dramatically enhance the emission intensity of Ln³⁺ ion. And under 980 nm laser excitation, the Yb³⁺/Er³⁺ and Yb³⁺/Ho³⁺ doped NaLuF₄ samples exhibit light green and yellowish green UC luminescence, respectively. This effective and low-cost chemical conversion method, combined with the novel structure and excellent optical luminescent properties of the as-prepared β-NaLuF₄ nanocrystals, may endow this luminescent structure with promising potential to serve as biomedical candidates, solid-state lasers and display devices.