Two-dimensional β-NaLuF4 hexagonal microplates

A simple hydrothermal method has been developed to synthesize monodisperse beta-NaLuF4 microplates in a large scale. The microcrystals have a perfect hexagonal shape with a diameter of about 5.2 mu m and a thickness of 300 nm. Trisodium citrate (Cit(3-)), which is introduced into the reaction mixture and acts as the chelating agent and shape modifier, plays a key role in fine-tuning the microstructures. The dominant adsorption of Cit(3-) onto the {0001} facets lowers the surface energy of these facets. Consequently, the typical growth in the [0001] direction is prohibited, and the growth of nuclei is driven along the six symmetric directions +/-[10 (1) over bar0], +/-[1 (1) over bar 00], and +/-[01 (1) over bar0], which directly results in the formation of beta-NaLuF4 microplates. The microstructure and growth mechanism of beta-NaLuF4 microplates are discussed in detail. Additionally, we investigated the photoluminescence properties of beta-NaLuF4:Ln(3+) (Ln = Eu, Tb, and Yb/Er). This powerfully demonstrates that beta-NaLuF4 is an excellent host lattice for down-conversion and up-conversion luminescence of various optically active lanthanide ions.