Controlled Synthesis, Evolution Mechanisms, and Luminescent Properties of ScF_x:Ln (x = 2.76, 3) Nanocrystals

Kinetic or thermodynamic control has been employed to guide the selective synthesis of conventional organic compounds, and it should be a powerful tool as well for accessing unusual inorganic nanocrystals, particularly when a series of members with similar chemical compositions and phase structures exist. Indeed, a comprehensive mapping of the energy barrier distribution of each nanocrystal in a predefined reaction system will enable not only the precise synthesis of nanocrystals with expected sizes, morphologies, phase structures, and ultimately functionalities, but also disclosure of the evolution details of nanocrystals from one structure to another. Using ScF_x:Ln (x = 2.76, 3) series as a proof-of-concept, we have successfully mapped out the energy barriers that correspond to each of the ScF_x:Ln nanocrystals, unraveled suitable temperatures for each type of nanocrystal formation, recorded their phase transition procedures, and also discovered the relationships of the products at each reaction stage. To testify how this approach allows one to tailor the structure-related optical properties, different lanthanide-doped ScF_x nanocrystals were synthesized and a wide-range of luminescence fine-tuning was achieved, which not only showcases high quality of the nanocrystals, but also provides more candidates for various luminescence applications, especially when single-particle upconversion emission is required.