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

Abstract

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.