Dropwise addition of cation solution: An approach for growing high-quality upconversion nanoparticles.

A suitable synthetic route and the associated reaction parameters play a vital role for growing high-quality nanocrystal. A design strategy of injection was introduced with the aim of enhancing monodispersity and crystallinity of upconversion nanoparticles and making them have uniform morphology. The high-quality Yb3+ /Er3+ -codoped LiYF4 , NaYF4 , KYF4 and NaGdF4 nanoparticles were synthesized by dropwise addition of cation solution into precursors mixture at high-temperature in this work. The detailed synthesis parameters of the purity tetragonal LiYF4 :Yb3+ /Er3+ upconversion nanoparticles in injection section were studied and ascertained. Changes of the injection temperature, reaction temperature, dropwise addition speed, mole ratio of cation (Li+ ) to precursors (RE(CF3 COO)3 ), reaction time and reactants concentration have contributed much to synthesizing high-quality LiYF4 :Yb3+ /Er3+ in the end. Compared with traditional thermal decomposition method, a series of properties, such as high crystallinity, less agglomeration phenomenon, uniform tetragonal bipyramidal morphology and great upconversion luminescence, could be improved by this modified method.