Crystalline phase and morphology controlling to enhance the up-conversion emission from NaYF4:Yb,Er nanocrystals

NaYF4:Yb,Er nanocrystals with different structures and sizes have been synthesized via a hydrothermal method. Structures and sizes of the NaYF4:Yb,Er nanocrystals are carefully investigated by changing the Gd3+ ion concentrations and reaction temperatures. It is found that the change of Gd3+ doping concentration and reaction temperature not only induces the phase transition but also causes the size difference. The introduction of Gd3+ ions can promote the phase change from cubic to hexagonal structures, which exhibit the different morphologies (nanoparticle vs nanorods). However, by increasing the reaction temperature slightly, the hexagonal structures can be formed with very low or even without any Gd3+ ions. It is shown that the enhanced up-conversion emission can be achieved by well controlling the Gd3+ ion concentrations at the certain reaction temperature to get the pure nanorods structures with suitable sizes.

145