Ligand effect on the synthesis of emission-tunable near-infrared Ag2S quantum dots

Ag2S quantum dots (QDs) are of great interest for the study of nanodiagnostics and in vivo imaging due to their appealing near-infrared fluorescence properties. However, the synthesis of small Ag2S QDs with well-controlled emission and size distribution is still difficult. Herein, a thiol-containing hot-injection method was developed for the preparation of small Ag2S QDs, and the ligand effect on the formation of Ag2S QDs was investigated. Ag(I) ions could be reduced by the oleylamine ligand to undesired Ag nanocrystals, and the 1-octanethiol ligand could suppress the reactivity of Ag(I) ions to avoid the reduction. The oleylamine ligand could activate the monomers and accelerate the nucleation and growth of the Ag2S QDs in the initial stage. Increase in the concentration of oleic acid with long hydrocarbon chain or decrease in the concentration of 1-octanethiol with short hydrocarbon chain could decelerate the growth of the Ag2S QDs due to steric factors and make the synthesis of small Ag2S QDs more controllable. Via modulating the ligand composition and growth time, the emission of Ag2S QDs could be tuned from 665 to 845 nm.