Oleic Acid/Oleylamine Cooperative-Controlled Crystallization Mechanism for Monodisperse Tetragonal Bipyramid NaLa(MoO4)2 Nanocrystals

A straightforward hydrothermal strategy for the controlled synthesis of monodisperse NaLa(MoO4)(2) and NaLa(MoO4)(2):Eu3+ bipyramid nanocrystals is presented using oleic acid/oleylamine as a mixed surfactant. Deprotonated oleic acid was demonstrated to be the decisive structure-directing agent for the bipyramid nanocrystals, and the bipyramid formation efficiency of the oleic acid/oleylamine combination was found to be the highest among the selected surfactant combinations. The roles of oleylamine in the synthesis of monodisperse bipyramid nanocrystals were elucidated. A possible oleic acid/oleylamine cooperative-control led crystallization mechanism (CCM) for the growth of uniform tetragonal bipyramid NaLa(MoO4)(2) nanocrystals is proposed on the basis of our experimental results. The formation of well-defined tetragonal bipyramid morphology is mainly due to the preferential adsorption of deprotonated oleic acid onto {101} and {001}, which changes the surface energy of crystal planes and leads to different growing rates along corresponding directions, while facilitating the formation of bipyramid morphology with exposed {101} faces. Fluorescent investigation revealed that NaLa(MoO4)(2):Eu3+ bipyramid nanocrystals possess a dominated hypersensitive red emission D-5(0) -> F-7(2) transition of Eu3+ at 613 nm.