Breaking through the Size Control Dilemma of Silver Chalcogenide Quantum Dots via Trialkylphosphine-Induced Ripening: Leading to AgTe Emitting from 950 to 2100 nm.

AgTe is one of the most promising semiconductors with a narrow band gap and low toxicity; however, it remains a challenge to tune the emission of AgTe quantum dots (QDs) precisely and continuously in a wide range. Herein, AgTe QDs emitting from 950 to 2100 nm have been synthesized via trialkylphosphine-controlled growth. Trialkylphosphine has been found to induce the dissolution of small-sized AgTe QDs due to its stronger ability to coordinate to the Ag ion than that of 1-octanethiol, predicated by the density functional theory. By controlling this dissolution effect, the monomer supply kinetics can be regulated, achieving precise size control of AgTe QDs. This synthetic strategy results in state-of-the-art silver-based QDs with emission tunability. Only by taking advantage of such an ultrawide emission has the sizing curve of AgTe been obtained. Moreover, the absolute photoluminescence quantum yield of AgTe QDs can reach 12.0% due to their well-passivated Ag-enriched surface with a density of 5.0 ligands/nm, facilitating noninvasive fluorescence imaging. The high brightness in the long-wavelength near-infrared (NIR) region makes the cerebral vasculature and the tiny vessel with a width of only 60 μm clearly discriminable. This work reveals a nonclassical growth mechanism of AgTe QDs, providing new insight into precisely controlling the size and corresponding photoluminescence properties of semiconductor nanocrystals. The ultrasmall, low-toxicity, emission-tunable, and bright NIR-II AgTe QDs synthesized in this work offer a tremendous promise for multicolor and deep-tissue fluorescence imaging.