Ni Zhang, Jin Xu, Shaohua Yu, Xiaoying Shang, Shan Lu, Datao Tu, Zhiyuan Xiao, Yao Lin, Xueyuan Chen
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.