Pb-Doped Ag₂ Se Quantum Dots with Enhanced Photoluminescence in the NIR-II Window

Ag₂ Se quantum dots (QDs) as an effective biological probe in the second near-infrared window (NIR-II, 1000-1700 nm) have been widely applied in bioimaging with high tissue penetration depth and high spatiotemporal resolution. However, the ions deficiency and crystal defects caused by the high Ag⁺ mobility in Ag₂ Se crystals are mainly responsible for the inefficient photoluminescence (PL) of Ag₂ Se QDs. Herein, a tailored route is reported to achieve controllable doping of Ag₂ Se QDs in which Ag is exchanged by Pb via cation exchange (CE), which is unattainable by direct synthetic methods. The Pb-doped Ag₂ Se QDs (denoted as Pb:Ag₂ Se QDs) present fire-new optical features with significantly enhanced PL intensity of 4.2 folds. Photoelectron spectroscopy confirms that Pb acts as an n-type dopant for Ag₂ Se QDs and therefore the electronic impurities provide additional carriers to fill the traps. Moreover, the general validity of this method is demonstrated to convert different sized Ag₂ Se into Pb:Ag₂ Se QDs, so that a wide range of NIR-II PL with high intensity is obtained. The bright NIR-II emission of Pb:Ag₂ Se QDs is further successfully performed in lymphatic system mapping.