Large-Scale Synthesis of High-Quality Metal Sulfide Semiconductor Quantum Dots with Tunable Surface-Plasmon Resonance Frequencies

High-quality CdS and Cu7S4 quantum dots (QDs) were synthesized with N,N-dibutylthiourea (DBTU) as an organic sulfur source. In this method, nucleation and growth reactions were controlled simply by the heating rate of the reaction. The mild oxidation conditions gave monodisperse CdS QDs exhibiting pure band-edge emission with relatively high photoluminescence quantum yield. During the synthesis of Cu7S4 QDs, the addition of dodecanethiol to the reaction system controlled the reaction rate to give monodisperse spherical or disk-shaped QDs. A hundred-gram scale of copper precursor could be used to generate the high-quality Cu7S4 QDs, indicating that an industrial-scale reaction is achievable with our method. As observed in anisotropic noble-metal nanocrystals, larger disk-shaped Cu7S4 QDs showed lower localized-surface-plasmon resonance energy in the near-infrared region. The disk-shaped Cu7S4 QDs could be used effectively as templates to form cation-exchanged monodisperse disk-shaped CdS QDs.