Shape-controlled synthesis and self-assembly of highly uniform upconverting calcium fluoride nanocrystals

Herein, the size- and shape-controlled synthesis of nearly-monodisperse, lanthanide-doped calcium fluoride (CaF2) nanocrystals (NCs) is reported. The sizes and shapes of CaF2 NCs are controlled by tailoring the reaction conditions, such as the concentration of lithium fluoride precursors, reaction time and temperature, and the procedure for adding the calcium trifluoroacetate precursors in the reaction mixture. Highly uniform CaF2 NCs are synthesized with several morphologies, such as nanospheres, truncated octahedra, nanoplates, and nanowires. The shape-controlled CaF2 NCs self-assemble into NC superlattices with long-range orientational and positional order forming crystalline and liquid crystalline structures. The near-infrared-to-visible upconversion luminescence properties are investigated by varying the types of dopants as well as the sizes and shapes of the CaF2 NCs. A novel synthetic method to tailor the shapes of highly uniform upconverting CaF2 NCs is demonstrated. We investigate the shape-dependent self-assemblies, and size, shape, and dopant composition-dependent upconversion luminescence of CaF2 NCs.