Dielectric Confinement Enables Molecular Coupling in Stacked Colloidal Nanoplatelets

TL;DR

This paper demonstrates theoretically that dielectric confinement in stacked colloidal nanoplatelets induces molecular coupling, leading to miniband formation and complex excitonic spectra, which could enable new nanocrystal chemistry applications.

Contribution

It introduces a novel mechanism of molecular coupling in colloidal nanoplatelets driven by dielectric confinement, distinct from quantum tunneling.

Findings

Energy levels redshift and split in stacked NPLs.

Formation of minibands of several meV width.

Rich excitonic absorption spectra with bright and dark states.

Abstract

We show theoretically that carriers confined in semiconductor colloidal nanoplatelets (NPLs) sense the presence of neighbor, cofacially stacked NPLs in their energy spectrum. When approaching identical NPLs, the otherwise degenerate energy levels redshift and split, forming (for large stacks) minibands of several meV width. Unlike in epitaxial structures, the molecular behavior does not result from quantum tunneling but from changes in the dielectric confinement. The associated excitonic absorption spectrum shows a rich structure of bright and dark states, whose optical activity and multiplicity can be understood from reflection symmetry and Coulomb tunneling. We predict spectroscopic signatures which should confirm the formation of molecular states, whose practical realization would pave the way to the development of nanocrystal chemistry based on NPLs.