Multiexciton absorption cross-sections of CdSe@CdS nanorods studied using Pump-rePump-Probe Spectroscopy

Understanding the multiexciton properties of nanocrystals is the basis for harnessing their full potential for various device applications. The multiexciton dynamics in semiconductor nanocrystals are widely explored. However, the absorption cross-sections for multiexcitons of varying order are not so well understood. To gain insights into the absorption cross sections for multiexcitons, we performed pump-repump-probe transient absorption (ppp-TA) spectroscopic measurement on CdSe@CdS nanorods. By tuning the pump-repump delay time and repump intensity, we were able to generate and reexcite various transiently living multiexcitonic species. We modelled the ppp-TA data using a Markov Chain Monte Carlo target analysis method, with this we determined the spectral shape and lifetime of higher order excitons (up to tri-excitons). This method also enabled us to extract absorption cross-section parameters for different multiexcitonic states. Our results indicate that for 400 nm excitation, the absorption cross-sections of excited state species are largely independent of exciton order.