Synthesis of High-Quality Metal Sulfide Nanoparticles from Alkyl Xanthate Single Precursors in Alkylamine Solvents

Abstract

A synthesis of various metal sulfide nanoparticles at relatively low temperature with use of a single precursor under ambient conditions is described. Metal alkyl xanthates (as well as thiocarbamates and thiocarbonates) are used as the precursor. Lewis base alkylamine solvents promote the reaction at low temperatures (from below room temperature up to ∼150 °C). By this method we form crystalline particles which are size- and shape-tunable and are usually monodiserse. This tunability is achieved by controlling parameters such as the reaction temperature, the reaction time, the concentration of the precursor, and the alkyl chain length. Core/shell structures are synthesized with the same method, using the same precursors, applying either a single-step or a dual-step process. CdS spherical particles, for instance, exhibit a narrow (∼30 nm fwhm) tunable excitonic fluorescence, and a broad, long wavelength defect emission, which intensity can be adjusted in a controlled manner, and even totally eliminated. Quantum yields of these particles are ∼2% for the “bare” particles and ∼16% for the ZnS-shelled, annealed particles. A short-wavelength (390−420 nm) narrow (30−35 nm fwhm) excitonic emission is observed for ZnS/CdS structures.