Spatial control of Nd³⁺ sensitizer in 808 nm excited upconversion nanocrystals towards nearly 100% energy migration...

808 nm excited energy migration upconversion (EMU) nanocrystals (NCs) exhibit great superiority over their 980 nm excited counterparts in alleviating the overheating effect of excitation laser in biodetection and imaging applications based on EMU NCs. However, it remains challenging to fabricate 808 nm excited EMU NCs to acquire the strong EMU emissions of Tb³⁺ or Eu³⁺ while simultaneously suppressing the ultraviolet (UV) upconversion emissions of Tm³⁺ and Gd³⁺ that cause the issue of autofluorescence interference. Herein, we report a novel sandwich structured core-triple shell NaLuF₄:Nd,Yb@NaLuF₄:Yb@NaGdF₄:Tm@NaLuF₄:Tb (or Eu) NC, wherein the efficiency of five-photon upconversion energy migration (i.e., Tm³⁺ → Gd³⁺ → Tb³⁺ (or Eu³⁺)) can approach 100% upon 808 nm excitation with power density above a threshold of ∼150 W cm^-2, thus resulting in the nearly complete inhibition of UV upconversion emissions of Tm³⁺ and Gd³⁺ concomitant with the strong EMU emissions of Tb³⁺ or Eu³⁺. Our findings may open new opportunities for further bioapplications of EMU NCs.