Enhancing Dye-Triplet-Sensitized Upconversion Emission Through Heavy Atom Effect in CsLu2F7:Yb/Er Nanoprobes.

Lanthanide (Ln 3+ )-doped upconversion (UC) nanoprobes, which have drawn extensive attentions for various bioapplications, usually suffer from small absorption cross-section and weak luminescence intensity of Ln 3+  ions. Herein, we report the controlled synthesis of a new class of Ln 3+ -doped UC nanoprobes based on CsLu 2 F 7 :Yb/Er nanocrystals (NCs), which can effectively increase the intersystem crossing (ISC) efficiency from singlet excited state to triplet excited state of IR808 up to 99.3% through the heavy atom effect. By virtue of the efficient triplet sensitization of IR808, the optimal UC luminescence (UCL) intensity of IR808-modified CsLu 2 F 7 :Yb/Er NCs is enhanced by 1309 times upon excitation at 808 nm. The enhancement factor is more than one order of magnitude higher than that based on the well-established NaYF 4 :Yb/Er NCs. Benefiting from the intense dye-triplet-sensitized UCL, the nanoprobes are demonstrated for sensitive assay of extracellular and intracellular hypochlorite with an 808-nm/980-nm dual excited ratiometric strategy, thus revealing the great potential of the proposed nanoprobes for monitoring biomolecules and biochemical processes in live cells.