Selected synthesis of cubic and hexagonal NaYF4 crystals via a complex-assisted hydrothermal route

Cubic nano-spheres and hexagonal microprisms of sodium yttrium tetrafluoride (NaYF4) have successfully been prepared separately via a mild hydrothermal route. The morphology and the structure of the NaYF4 crystals can be changed by adjusting the Y3+/F− ratio in the reaction solution. Cubic NaYF4 nano-spheres are synthesized when the Y3+/F− ratio is stoichiometric; while hexagonal NaYF4 microprisms appear as excess F− is present at 180 °C for more than 5 h. Ethylenediamine tetra-acetic acid (EDTA) plays an important role as a chelating ligand, and F− acts as both a reactant and a mineralizer during the synthesis process. A growth mechanism is discussed.