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

Abstract

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.