Controlled synthesis of ultrasmall hexagonal NaTm_(0.02)Lu_(0.98-x)Yb_xF4 nanocrystals with enhanced upconversion luminescence

摘要

Ultrasmall upconversion (UC) nanoparticles with intense luminescence are quite desirable for in vitro and in vivo bioimaging. Herein, we report the successful synthesis of sub-10 nm hexagonal NaTm_(0.02)Lu_(0.98-x)Yb_xF4 nanocrystals via a high boiling solvent process. The sizes and phases of the crystals can be finely tailored by tuning the amounts of the ligands used (octadecylamine and sodium oleate) and the temperature. The intensity of the UC emission of the nanocrystals increases as the relative content of Yb~(3+) ions increases from 20% to 98%, owing to improved near-infrared absorption and energy-transfer from Yb~(3+) to Tm~(3+). The experimental results indicate that hexagonal NaYbF4 is the best host for ultrasmall Tm~(3+)-doped UC nanoparticles and shows great potential in biomedical applications.