Energy Transfer from Multiple Excitons in a Perovskite Nanocrystal to Organic Dyes Revealed by Single-Particle Spectroscopy

Colloidal semiconductor quantum dots (QDs) can generate multiple excitons (MXs) within a single QD. Owing to their large absorption cross-section, efficient utilization of MX is anticipated for the development of light-harvesting systems. However, MXs typically undergo nonradiative decay via Auger recombination (AR). In this study, we investigated the possibility of energy transfer from the MXs in a single QD to multiple cyanine dyes (Cy3) adsorbed on the QD surface. Based on the linear relationship between the AR lifetime and QD volume, formamidinium lead bromide perovskite nanocrystals (PNCs) with three distinct size distributions were synthesized. Simultaneous measurements of emission photon correlations and individual pristine PNC sizes revealed that the probability of multiphoton emission increased in PNCs larger than 12 nm. This was attributed to a slowdown in the AR rate, which was evaluated by transient absorption spectroscopy. Subsequently, multiple Cy3 dyes were adsorbed onto the PNCs as energy acceptors to evaluate the transfer of energy from the MXs to multiple Cy3 dyes. Photon correlation measurements of Cy3 emission via energy transfer─induced by excitation of a single PNC─showed an increased probability of multiphoton emission in PNC-Cy3 systems with PNC sizes exceeding 12 nm. These findings indicate that multiple Cy3 dyes were excited and emitted via the energy transfer from MXs. Thus, we clearly demonstrate that energy transfer from MXs to multiple surface dyes is feasible using large-sized PNCs.