Tuning Intermediate-Band Cu₃VS₄ Nanocrystals from Plasmonic-like to Excitonic via Shell-Coating

Colloidal nanocrystals (NCs) can be generally classified as either excitonic or plasmonic. Excitonic NCs can find applications in photocatalysis and light emitting devices; in contrast, plasmonic NCs can be applied for sensing, nanophotonics, and photothermal conversion, although it is noteworthy that photocatalysis based on plasmon-induced hot carrier transfer is also emerging as an important field. Here we report that Cu3VS4 NCs, an intermediate-band material, can be tuned from plasmonic-like to excitonic simply via coating with CdS shells. The plasmonic-like behaviors of pristine Cu3VS4 NCs were confirmed by the spectral and dynamic properties of their optical resonances studied using transient absorption (TA) spectroscopy. Upon shell coating, the Cu3VS4/CdS core/shell NCs became quasi-type II hetero-NCs, with an emission quantum yield of ∼10% and an exciton lifetime of ∼600 ns. Because of effective electron delocalization throughout Cu3VS4 and CdS, we also demonstrated ultrafast and efficient electron extraction from the core/shell NCs. The tunability from plasmonic-like to excitonic behaviors is enabled by state mixing between the core and the shell, which is not limited to Cu3VS4 NCs but should be universally applicable to many other intermediate-band materials. Such a general strategy should greatly enrich the toolbox of colloidal NCs for many emerging applications.