A facile route to the synthesis of sub-5Â nm monodispersed cubic NaYF4: Yb3+/Er3+ nanocrystals

The synthesis of ultrasmall upconversion nanophosphors is of great importance due to their potential applications in biomedicines. In this report, sub-5 nm monodispersed cubic NaYF4: Yb3+/Er3+ nanocrystals were synthesized by a facile method. The nanocrystals have been well characterized and the average diameter was determined to be about 3.5 nm ±0.4 nm, which is one of the smallest grain sizes for NaYF4: Yb3+/Er3+ nanocrystals ever reported. The size of the nanocrystals can be modulated by increasing the reaction temperature. Other reaction conditions including contents of OA and ODE as well as amount of NaOH were also investigated and their effects on the phase and morphology of NaYF4: Yb3+/Er3+ nanocrystals have been elucidated.