Pb ions enhanced fluorescence of Ag2S QDs with tunable emission in the NIR-II window: Facile one pot synthesis and their application in NIR-II fluorescent bio-sensing

Ag2S quantum dots (QDs) are good candidate for tuning its emission in the second near-infrared (NIR-II) window due to its narrow band gap. But the high Ag+ mobility in Ag2S nanocrystals causes plenty of cation deficiency, which lead to the lattice defects of NIR-II Ag2S QDs. In this paper, Ag2S QDs were doped with different metal cations by a facile one-pot synthesis method. The Pb-doped Ag2S QDs showed the highest fluorescence quantum yield (FLQY) with tunable emission in the range of 950-1200 nm. Also the reaction time is significantly shortened in the synthetic process. Furthermore, the feeding atomic ratio of Pb2+/Ag+ was varied to investigate its effect on the structure and FL of the QDs. As the ratio increased, the crystal structure changed from a single monoclinic-Ag2S to the monoclinic-Ag2S and PbS nanocrystals, demonstrating the production of silver-lead sulfide QDs. Also it is found the FL increased when the level of Pb-doping increased and then reached maximum at the ratio of 2:1 (Pb2+:Ag+). It is believed that the doping strategy achieves high-quality and low-energy synthesis of Ag2S QDs. At last, the NIR-II fluorescence silver-lead sulfide QDs were utilized to construct a highly sensitive and selective H2O2 biosensor, which used for the real biological sample analysis.