Multiexciton Absorption Cross Sections of CdSe Quantum Dots Determined by Ultrafast Spectroscopy

Abstract

Multiexciton absorption cross sections are important for analysis of a number of experiments, including multiple exciton generation and stimulated emisson. We present a rigorous method to determine these cross sections using transient absorption (TA) measurements. We apply the method to CdSe quantum dots (QDs) and core-shell (CdSe)ZnS QDs. The method involves measuring TA dynamics for various excitation intensities over a broad time range and analyzing the experiments in terms of a kinetic multiexciton model taking into account all contributions to the signal. In this way, we were able to quantify exciton and multiexciton absorption cross sections at different spectral positions. The absorption cross sections decrease with increasing number of excitations, qualitatively in agreement with the state-filling effective mass model but showing a slower decrease. The cross sections for single-exciton to biexciton absorption range between 57 and 99% of the ground to single-exciton cross section.

Quantum coherence of multiple excitons governs absorption cross-sections of PbS/CdS core/shell nanocrystals

“…The efficient Auger recombination in NCs is evidence of strong many-body interactions and a deviation from the Poisson model has been discussed for multiple excitons 17 . Furthermore, it has been reported that multiple exciton absorption cross-sections are altered by state filling 18 . Both the model with identical and that with altered absorption cross-sections are used, depending on the experiments.…”

Ultrafast photoinduced dynamics in quantum dot-based systems for light harvesting

“…In fact, recent work shows that the absorption cross-section of a multi-exciton does not scale linearly with the number of the excitons [105]. In a typical pump-probe spectroscopy the bleach signal from the bi-excitons decays at a faster rate (tens of picoseconds) while that from the single excitons decays on much slower timescale (tens of nanoseconds), as shown in Fig.…”

Deciphering hot- and multi-exciton dynamics in core–shell QDs by 2D electronic spectroscopies

“…, exciton, BX, and TX recombinations), whose relative amplitude should follow a Poissonian behavior. 57 …”

“…Noteworthily, according to the universal curve by Klimov, the slower saturation of biexciton species ( E sat,X = 47 nJ; E sat,BX = 158 nJ) can be ascribed to a reduction of the absorption cross section for BX, as previously reported by Pullerits. 41 , 57 Further details on the power-dependent global fitting can be found in the ESI. † On the other hand, no saturation is observed for the DAS related to TX, due to the involvement of a highly degenerate |1P On the other hand, no saturation is observed for the DAS related to TX, due to the involvement of a highly degenerate |1P〉 state.…”