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(CF₃COO)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.