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

Abstract

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.