Controllable synthesis of β-NaYF4:Yb,Er nanorods by potassium oleate as ligand

By using potassium oleate (KOL) as a part of ligand, nanorods of beta-NaYF4:Yb,Er were synthesized. The aspect ratio of beta-NaYF4:Yb,Er nanocrystals was tuned by changing the amount of KOL. We found that potassium from KOL is not only absorbed on the surface of nanocrystals, but also partially substitutes Na element in nanocrystals lattice. Different from the classical shape control mechanism that oleate ions are absorbed on different facets of nanocrystals, the anisotropic growth of beta-NaYF4:Yb,Er in current work is caused by the doping of K+. The incorporation of K+ would not lead to obvious decrease of the upconversion fluorescence intensity. Meanwhile, oleate ions promote the phase transition of nanocrystals from cubic to hexagonal phase, resulting in the simultaneous controllability of the nanocrystals size.