Uniform Alkaline Earth Fluoride Nanocrystals with Diverse Shapes Grown from Thermolysis of Metal Trifluoroacetates in Hot Surfactant Solutions

Uniform alkaline earth metal fluoride MF2 (M = Mg, Ca, and Sr) nanocrystals with various shapes (tetragonal MgF2 nanoneedle-constructed 3D networks; cubic CaF2 nanoplates and nanopolyhedra; cubic SrF2 nanoplates and nanowires) have been synthesized from the thermolysis of alkaline earth metal trifluoroacetate (M(CF3COO)(2)) in hot surfactant solutions (oleic acid, oleylamine, and I-octadecene). The MF2 nanocrystals were formed by the controlled fluorination of the M-O bond into the M-F bond at the nucleation stage and subsequent growth process. For phase-pure MF2 nanocrystals, the growth of shape-selective MF2 nanocrystals was likely due to the template direction of micellar structures formed by self-assembly of capping ligands and the so-called "Ostwald ripening" process. With the developed synthetic strategy, the uniform upconversion SrF2:Yb,Er and core/shell SrF2:Yb,Er@SrF2 nanocrystals were also obtained. The core/shell-structured nanocrystals exhibited enhanced emission intensity and saturation power with respect to their core counterparts, owing to the suppression of associated nonradiative decays.