Cu_(2-x)S/PbS Core/Shell Nanocrystals with Improved Chemical Stability

Abstract

Nanocrystals of doped semiconductors, such as Cu_(2-x)S, hold much promise for near infrared active devices because, unlike in noble metals, their tunable infrared plasmon can exist in nanocrystals with diameters <40 nm. Combining infrared plasmonic Cu_(2-x)S nanocrystals with infrared excitonic PbS nanocrystals has the potential to improve the optical properties of PbS nanocrystals via exciton–plasmon coupling. To explore this potential, we have developed the first synthetic method to deposit a PbS shell onto Cu_(2-x)S nanocrystals and confirmed the structure to have a mostly Cu_(2-x)S core with a patchy PbS shell using high-angle annular dark-field imaging scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy spectrum images. Addition of the PbS shell changes the crystallographic phase of the Cu_(2-x)S cores and blueshifts and enhances their infrared plasmonic resonance. The shell also provides chemical stability to the Cu_(2-x)S nanocrystals such that they no longer completely chemically quench the photoluminescence of neighboring excitonic PbS nanocrystals in assembled films; consequently, these Cu_(2-x)S/PbS core/shell nanocrystals will enable future studies of infrared exciton–plasmon coupling at the nanoscale. This work demonstrates the importance of understanding the chemical interactions between nanocrystals of different materials when characterizing their optoelectronic properties in mixtures and composite materials.