Orientation-Dependent Image Dipole Interaction for the Tuning of the Excitonic Properties of CdSe Nanoplatelets

The fundamental characteristics of semiconductor nanoplatelets (NPLs) have been intensively studied with a view to their use in various optoelectronic devices. In particular, the assembly of highly anisotropic NPLs into stacks allows their optical properties to be easily controlled. Here, we systematically investigate the radiative decay processes of NPL assemblies for two distinct configurations, face-down and edge-up, and find a new way of manipulating their excitonic properties by introducing metamaterial structures. While the exciton lifetime for face-down NPLs is not strongly affected by the metamaterials, a significant reduction in the exciton lifetime for edge-up NPLs is observed. We account for this interesting result in terms of orientation-dependent image dipole interactions by showing that the net transition dipole moments for the two NPL configurations can be affected inversely by metamaterials. These results will facilitate the development of optoelectronic applications requiring the active manipulation of exciton lifetimes.