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 LiYE4: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. (C) 2017 Elsevier Inc. All rights reserved.