Oleic acid/oleylamine cooperative-controlled crystallization mechanism for monodisperse tetragonal bipyramid nala(moO₄)2nanocrystals

A straightforward hydrothermal strategy for the controlled synthesis of monodisperse NaLa(MoO₄)₂and 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-controlled crystallization mechanism (CCM) for the growth of uniform tetragonal bipyramid NaLa(MoO₄)₂nanocrystals 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 ⁵D₀- ⁷F ₂transition of Eu3+at 613 nm.