CdSe Magic-Size Clusters Deviate from Nanocrystal-Size Scalings for Ultrafast Intraband Relaxation and Auger Recombination

The cluster regime of colloidal semiconductor quantum dots (QDs) occupies an interesting space on the continuum from molecule to bulk material and allows for the study of QD properties at extreme quantum confinement limits. For typical QDs, several size-dependent trends are well-established, including intraband relaxation rates and the universal scaling of Auger recombination with particle volume. Advances in synthesis now allow isolation of atomically precise semiconductor magic-size clusters (MCs), which offer experimental insight regarding how the electronic structure changes with the particle size in the ultrasmall limit. We report intraband cooling and Auger recombination for several stable CdSe MCs as a function of the particle size and observe deviation from the QD response in the cluster regime. We additionally present optical signatures ascribed to transient disordering that appear in the single-exciton regime for MCs, which point to complexities regarding the implementation of MCs in optoelectronic devices.