Browsing by Subject "Biexciton"

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Open Access
Multi-exciton states in flexible Rydberg aggregates
(2017-06) Abumwis, Ghassan F.M.
Flexible Rydberg aggregates, assemblies of highly excited atoms, provide a platform to investigate quantum phenomena like energy transport and conical intersections. This can be achieved by doping the aggregate with an excitation, an excited state that is energetically higher but close to the primary Rydberg state, which results in the resonant dipole-dipole interaction becoming dominant. Consequently, the excitation is delocalized throughout the aggregate leading to the creation of exciton states. The properties of excitons have been studied for aggregates with a single excitation only. We follow up on previous results and add a second excitation to the system. Here, we demonstrate that most biexciton states for a dislocated chain at one end, a chain with equal spacing between atoms except for the last two, can be expressed as products of single exciton states. Moreover, we present the atomic trajectories for each biexciton state and we show that non-adiabatic effects are quite prominent in exible chains of Rydberg atoms. Finally, we analyze the interaction between two excitation pulses based on the initial biexciton state and the presence of a dislocation, then we show some cases where a transmission switch behavior is observable. Our ndings further enhance the range at which exible Rydberg aggregates can be used to model chemical quantum processes that take place in light harvesting molecules and molecular aggregates. Furthermore, the transmission switch behavior opens the possibility of using Rydberg aggregates in quantum information processing.
Open Access
Observation of biexcitons in nanocrystal solids in the presence of photocharging
(American Chemical Society, 2013) Cihan, A. F.; Martinez, P. L. H.; Kelestemur Y.; Mutlugun, E.; Demir, Hilmi Volkan
T In nanocrystal quantum dots (NQDs), generating multiexcitons offers an enabling tool for enhancing NQD-based devices. However, the photocharging effect makes understanding multiexciton kinetics in NQD solids fundamentally challenging, which is critically important for solid-state devices. To date, this lack of understanding and the spectral temporal aspects of the multiexciton recombination still remain unresolved in solid NQD ensembles, which is mainly due to the confusion with recombination of carriers in charged NQDs. In this work, we reveal the spectral temporal behavior of biexcitons (BXs) in the presence of photocharging using near-unity quantum yield CdSe/CdS NQDs exhibiting substantial suppression of Auger recombination. Here, recombinations of biexcitons and single excitons (Xs) are successfully resolved in the presence of trions in the ensemble measurements of time-correlated single-photon counting at variable excitation intensities and varying emission wavelengths. The spectral behaviors of BXs and Xs are obtained for three NQD samples with different core sizes, revealing the strength tunability of the X X interaction energy in these NQDs. The extraction of spectrally resolved X, BX, and trion kinetics, which are otherwise spectrally unresolved, is enabled by our approach introducing integrated time-resolved fluorescence. The results are further experimentally verified by cross-checking excitation intensity and exposure time dependencies as well as the temporal evolutions of the photoluminescence spectra, all of which prove to be consistent. The BX and X energies are also confirmed by theoretical calculations. These findings fill an important gap in understanding the spectral dynamics of multiexcitons in such NQD solids under the influence of photocharging effects, paving the way to engineering of multiexciton kinetics in nanocrystal optoelectronics, including NQD-based lasing, photovoltaics, and photodetection.