Correlated Microspectroscopy and Electron Microscopy of Binary Superlattices of Infrared Plasmonic and Excitonic...

Devices made from colloidal nanocrystals contain films of randomly arranged nanocrystals that lack long-range order. Controlling the periodic arrangement of these nanocrystals into superlattices can generate engineered metamaterials that exhibit properties not achievable in natural semiconductors or in disordered films of nanocrystals. The current size of ordered domains in these materials (analogous to grain size in polycrystalline materials), however, is typically microscopic, so the field lacks detailed structure-property relationships. Expanding on our previous work, we have engineered the surface chemistry of our nanocrystals to create enlarged domains of binary nanocrystal superlattices of infrared plasmonic Cu_2-xS/PbS core-shell and excitonic PbS nanocrystals. We then directly correlated photoluminescence microscopy with transmission electron microscopy of the binary superlattices and single-component PbS superlattices. The PbS nanocrystals within the binary superlattices were still nearly as luminescent as their counterparts in single-component PbS superlattices, and they exhibited photoluminescence decay dynamics 30 times faster, suggesting that both the radiative and nonradiative decay rates were accelerated. A pronounced redshift of 80 meV was also observed in the emission from the binary superlattices relative to that of the single-component PbS superlattices. In the future, we envision that combining measurements of individual superlattice domains with optical modeling will further our understanding of multicomponent nanocrystal superlattices and allow us to create desired properties such as bright and fast infrared emission by design.