Generalized one-pot synthesis of copper sulfide, selenide-sulfide, and telluride-sulfide nanoparticles

Here we report a facile approach to synthesize copper chalcogenide (Cu _2-xS, Cu_2-xSe_yS_1-y and Cu _2-xTe_yS_1-y) nanocrystals without employing hot-injection, at moderate reaction temperatures (200-220 C) and free of phosphines. Scaling up of the synthesis yields monodisperse nanoparticles without variations in their morphology. We have observed the formation of alloyed copper selenide-sulfide and telluride-sulfide nanocrystals due to the incorporation of sulfur by using 1-dodecanethiol as a ligand along with oleic acid. The materials obtained possess localized surface plasmon resonances in the near-infrared region, which are demonstrated to be widely tunable via a controlled oxidation generating copper vacancies. Copper sulfide nanoparticles with well-defined initial chalcocite crystal phase were subjected to oxidation followed by structural characterization. Structural rearrangement of the oxidized chalcocite Cu_2-xS crystal lattice to roxbyite by aging is proven to release the copper vacancies. Further oxidation again can create new copper vacancies in the roxbyite lattice, however its structure does not evolve into covellite CuS. These findings suggest that besides nonstoichiometry (i.e., the value of x) induced by oxidation, crystal structure is an important factor responsible for plasmonic properties of copper chalcogenide nanocrystals. Furthermore, successful water solubilization of Cu_2-xTe _yS_1-y nanoparticles with preservation of their plasmon band has been realized via a ligand exchange approach employing a mPEG-SH stabilizer.