Single-crystalline and near-monodispersed NaMF3 (M = Mn, Co, Ni, Mg) and LiMAlF6 (M = Ca, Sr) nanocrystals from cothermolysis of multiple trifluoroacetates in solution.

We report the synthesis of single-crystalline and near-monodispersed NaMF3 (M = Mn, Co, Ni, Mg), LiMAlF6 (M = Ca, Sr), and NaMgF3:Yb,Er nanocrystals (quasisquare nanoplates, nanorods, and nanopolygons) by the cothermolysis of multiple trifluoroacetates in hot combined organic solvents (oleic acid, oleylamine, and 1-octadecene). The nanocrystals were characterized by XRD, TEM, superconductive quantum interference device (SQUID), and upconversion luminescence spectroscopy. By regulating the polarity of the dispersant, the NaMF3 (M = Mn, Co, Ni) nanoplates were partially aligned to form nanoarrays on copper TEM grids. The sizes of the NaMF3 nanocrystals were easily tuned by the use of proper synthetic conditions such as reaction temperature and time and solvent composition. On the basis of a series of experiments in which the reaction conditions were varied, together with GC-MS and FTIR analysis, the reaction pathways for the formation of these nanocrystals from trifluoroacetate precursors were proposed. The magnetic measurements showed that the differently sized NaMnF3 square plates displayed interesting weak ferromagnetic behavior on the nanometer scale. The strong red upconversion luminescence emitted from the NaMgF3:Yb,Er nanorods under 980-nm near-IR laser excitation suggests that NaMgF3 may be a good candidate host material for red upconversion luminescence.