Core-shell nanoarchitecture: a strategy to significantly enhance white-light upconversion of lanthanide-doped nanoparticles

We report that the upconversion white-light luminescence in ultrasmall CaF2:Yb/Tm/Ho nanoparticles has been enhanced by more than one order of magnitude through growing the Yb3+-containing NaYF4 shell. Such white-light enhancement achieved in the ultrasmall (sub-10 nm) core-shell nanocrystals is attributed to the surface protection and the efficient energy transfer from the active shell which not only protects the lanthanide emitters located in the core especially those near the surface from quenchers at the surface (e.g., defect, organic ligands, etc.) but also absorbs more excitation energy due to the additionally incorporated Yb3+ in the shell. The result suggests an effective approach to significantly improve the white-light emission of lanthanide-doped nanocrystals which show great potential in diverse industrial as well as newly emerging biomedical applications.