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

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.