Enhanced 808 nm driven Ce3+ doped red-emitting upconversion nanocrystals by intercalated nanostructures

We report the red but weak upconversion luminescence of core-shell-shell structured upconversion nanocrystals (NaYF4:Yb/Ho/Ce@NaYF4:Nd@NaYF4) under excitation at 808 nm due to high surface Ce3+ concentration in core nanocrystals hindering the energy transfer from the Nd3+ shell to the Yb3+ core. 10.2-fold upconversion luminescence enhancement was achieved by conquering the negative effects of non-uniform Ce3+ distribution phenomena on upconversion processes via intercalating NaYF4:Yb/Ho/Ce, designed as the shell, into the Nd3+ sensitized nanostructure (NaYF4:Nd@NaYF4:Yb/Ho/Ce@NaYF4: Nd@NaYF4:Yb/Ho/Ce@NaYF4). The intercalation nanostructured upconversion nanocrystals show intense red upconversion luminescence with a red-to-green ratio of 5.0. Bright red upconversion luminescence of the Ce3+ doped intercalation nanostructured upconversion nanocrystals embedded in biological tissues can be visualized even at a depth of 5 mm illuminated by 808 nm laser light. High efficiency 808 nm driven red-emitting upconversion nanocrystals are promising for bio-applications.