Multiexciton absorption cross sections of CdSe@CdS nanorods studied using pump-repump-probe spectroscopy

While the multiexciton dynamics in semiconductor nanocrystals is widely explored, to determine the absorption cross sections for multiexcitons of varying order is still a challenge. In this study, we performed pump-repump-probe transient absorption (ppp-TA) spectroscopic measurements on CdSe@CdS nanorods to gain insights into the absorption cross sections for multiexcitons. By tuning the pump-repump delay time and repump intensity, we were able to generate and reexcite various transiently living multiexcitonic species distributions. By modelling the ppp-TA data using a Markov Chain Monte Carlo target analysis method, the spectral shape and lifetime of higher order excitons (up to tri-excitons), and absorption cross section parameters for different multiexcitonic species are accessible. We find that at the repump wavelength 400 nm used in this study the absorption cross sections of the exciton and multiexciton species are smaller compared to the ground state species. The determined values indicate that the biexciton absorption cross section at 400 nm is slightly larger than the cross section for the monoexciton and triexciton determined in our study.