Nature and Control of Shakeup Processes in Colloidal Nanoplatelets

Recent experiments suggest that the photoluminescence line width of CdSe nanoplatelets (NPLs) and core/shell CdSe/CdS NPLs may be broadened by the presence of shakeup (SU) lines from negatively charged trions. We carry out a theoretical analysis, based on effective mass and configuration interaction (CI) simulations, to identify the physical conditions that enable such processes. We confirm that trions in colloidal NPLs are susceptible of presenting SU lines up to 1 order of magnitude stronger than in epitaxial quantum wells, stimulated by dielectric confinement. For these processes to take place, trions must be weakly bound to off-centered charge traps, which relax symmetry selection rules. Charges on the lateral sidewalls are particularly efficient to this end. Our simulations display a single strong SU replica in most instances, which agrees well with experiments on CdSe NPLs, but suggests that the multipeaked emission reported for core/shell CdSe/CdS NPLs must involve other factors beyond SU processes. We propose emission from a metastable spin triplet trion state may be responsible. Understanding the origin of SU processes may open paths to rational design of NPLs with narrower line width.