Aspect-Ratio Controlled Synthesis and Tunable Luminescence of YF3:Yb3+/Er3+ Upconversion Nanocrystals

We report a facile synthetic method for high-aspect-ratio YF3:Yb3+/Er3+ nanocrystals by controlling the composition of the precursor and salts to manipulate the structures of YF3:Yb3+/Er3+ nanocrystals. A controlled aspect ratio is attained by tuning the molar ratio of NH4+/RE3+ (NH4+ is the counterion released from the fluoride precursor (NH4F) and RE3+ indicates the total amount of Y, Yb, and Er) and the presence of specific inorganic salts. A low molar ratio of NH4+/RE3+ induced the production of high-aspect-ratio YF3:Yb3+/Er3+ nanocrystals, while a high molar ratio of NH4+/RE3+ induced the formation of irregular nanoplates. The selection of the inorganic salt as an additive is critical in controlling the aspect ratio and crystallinity of YF3:Yb3+/Er3+ nanocrystals. The cation showed limited control over the aspect ratio, but the anions, Cl– and Br–, induced the production of the highest aspect ratio for YF3:Yb3+/Er3+ nanocrystals. We found that the aspect ratio affected the luminescence properties of ...