Synthesis And Application Of Rare Earth Fluoride Based Upconversion Nanocrystals

In recent years, lanthanide (Ln)-doped upconversion nanoparticles (UCNPs) despite limited quantum yields have attracted considerable attention owning to their superior chemical and optical properties, such as narrow emission peaks (<10 nm), long lifetimes (μs-ms range), large anti-stokes shifts, superior photostability, and low toxicity. Ln3+ binary doped LaF3, NaGdF4 and NaYF4 nanostructures have been regarded as the most commonly-used UC luminescent host materials and thus have been widely studied ranging from their synthetic strategies to their potential biological applications.The thesis can be divided into three parts:The first part is to synthesize Ln-doped NaGdF4 nanocrystals via oleic acid/BmimBF4 ionic liquid two-phase system. Without methanol, uniform and monodisperse oil-dispersible products can be prepared. When methanol was added, water-soluble products with larger size can be obtained. Actually, methanol played a very important role in regulating the dual-phase transition of the product. Then, water soluble NaGdF4:Yb, Er nanocrystals were applied in dual-mode imaging (upconversion luminescence imaging and CT imaging)The second part is to synthesize a series of rare-earth fluoride nanocrystals via oleic acid/BmimBF4 ionic liquid two-phase system, including LaF3, GdF3, NaGdF4, YF3, NaYF4, YbF3 and NaYbF4 oil-dispersed nanocrystals. Ln-doped NaGdF4 and NaYF4 water-soluble nanocrystals were also synthesized in IL phase. The as-prepared NaGdF4 nanocrystals were hexagonal phase while NaYF4 were a mixture of cubic and hexagonal phase.The third part is to synthesize hexagonal LaF3:Yb, Er; NaGdF4:Yb, Er and NaYF4:Yb, Er nanocrystals through n-octanol induced two-phase system. The role of n-octanol and BmimPF6 in phase and size control was discussed in detail. Then, Stober-based silica coating was conducted on water-soluble NaYF4:Yb, Er nanocrystals. Finally, cytotoxicity test was performed on the products before and after silica coating.The OA/ IL two phase system provided a new synthetic method in the synthesis of rare earth fluoride nanocrystals and has multiple advantages including the adoption of environmental-friendly regents, mild experimental conditions and one-step synthesis of water-soluble products.