Understanding the features in the ultrafast transient absorption spectra of CdSe quantum dots

Zhang, Cheng; Nhut, Thanh; Ong, Xuanwei; Chan, Yinthai; Tan, Howe‐Siang

doi:10.1016/j.chemphys.2016.08.027

Cited by 34 publications

(49 citation statements)

References 30 publications

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“…4B shows the impact of the ESA signal, which also gives rise to coherent signals. In semiconductor QDs, ESA and SE contributions overlap and cancel over most of the cross-peak (77). The net result shown in Fig.…”

Section: Discussionmentioning

confidence: 90%

Atomic fluctuations in electronic materials revealed by dephasing

Palato

Seiler

Nijjar

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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The microscopic origin and timescale of the fluctuations of the energies of electronic states has a significant impact on the properties of interest of electronic materials, with implication in fields ranging from photovoltaic devices to quantum information processing. Spectroscopic investigations of coherent dynamics provide a direct measurement of electronic fluctuations. Modern multidimensional spectroscopy techniques allow the mapping of coherent processes along multiple time or frequency axes and thus allow unprecedented discrimination between different sources of electronic dephasing. Exploiting modern abilities in coherence mapping in both amplitude and phase, we unravel dissipative processes of electronic coherences in the model system of CdSe quantum dots (QDs). The method allows the assignment of the nature of the observed coherence as vibrational or electronic. The expected coherence maps are obtained for the coherent longitudinal optical (LO) phonon, which serves as an internal standard and confirms the sensitivity of the technique. Fast dephasing is observed between the first two exciton states, despite their shared electron state and common environment. This result is contrary to predictions of the standard effective mass model for these materials, in which the exciton levels are strongly correlated through a common size dependence. In contrast, the experiment is in agreement with ab initio molecular dynamics of a single QD. Electronic dephasing in these materials is thus dominated by the realistic electronic structure arising from fluctuations at the atomic level rather than static size distribution. The analysis of electronic dephasing thereby uniquely enables the study of electronic fluctuations in complex materials.

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Section: Discussionmentioning

confidence: 90%

Atomic fluctuations in electronic materials revealed by dephasing

Palato

Seiler

Nijjar

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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show abstract

“…Careful determination of peak positions, the relative amplitude weightages and the biexciton binding energy shifts are of great importance in the simulation. All these parameters have been achieved with great accuracy in our previous study in TA measurements on CdSe QDs [201]. spectra with the ratio of inhomogeneous linewidth versus homogeneous linewidth varying from 0.5 to 1.5 for QDs system with the lowest two exciton states involved.…”

Section: Nls In Qds Ensemblesmentioning

confidence: 83%

“…and excited state absorption (ESA). The first two terms share the same negative sign, while the last term shows the opposite sign with a redshift referred as the biexciton binding energy shift [64,201]. The resulting peakshape is a pair of positive value peak to negative going peak in the corresponding transition positions.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…As documented in our previous study on CdSe QDs ensembles using TA spectroscopy [201], by carefully enumerating all possible double-sided Feyman diagrams (DSFDs) accounting for the corresponding GSB, SE and ESA signals and combining the hole state spin-doubly degeneracy condition, the TA signal can be simulated with the expression…”

Section: Transient Absorption Fittingmentioning

confidence: 99%

“…and spectral diffusion of a system is the nodal line slope (NLS) analysis [198]. [201]. We have enumerated all the processes that contribute to the features in the transient absorption spectrum.…”

Section: Introductionmentioning

confidence: 99%

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Applications of ultrafast multidimensional electronic spectroscopy to the study of plant light harvesting systems and colloidal quantum dots

Zhang¹

Self Cite

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This dissertation focuses on the development of ultrafast multidimensional electronic spectroscopy using a pump probe geometry and its application in discerning the energy transfer mechanics and band structure analysis on plant light-harvesting systems and colloidal quantum dots. In green plants, the first step of light absorbing processes is carried out and implemented by the light-harvesting complex II (LHCII). The trimeric and aggregated LHCII exhibit the unquenched and quenched excitonic states of Chlorophyll (Chl), respectively. Two-dimensional electronic spectroscopy (2DES) ,which allows direct observation of correlation of excitation and emission energy polls, enables the mapping of the pathways and dynamics from Chl b to Chl a to give insights into the mechanism of non-photochemical quenching that protects the system away from photodamage. Long-lived intermediate Chl a states are present in trimers, while in aggregates, the population decay of these excited states is significantly accelerated, suggesting that, overall, the energy transfer within the LHCII complexes is faster in the aggregated state. In addition, 2DES experiments under conditions free from singlet-singlet annihilation and anisotropic decay are done in the following study. The energy transfer between the different domains within the Chl a manifold is investigated and found to proceed on time scales ranging from hundreds of femtoseconds to five picoseconds, before reaching equilibration. The bidirectional (uphill and downhill) energy transfer of the equilibration process between excited states are clearly observed in experiments. Furthermore, exciton equilibration and excitation trapping in intact Photosystem I (PSI) complexes as well as core complexes isolated from Pisum sativum are studied.

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Ultrafast Electro‐Absorption Switching in Colloidal CdSe/CdS Core/Shell Quantum Dots Driven by Intense THz Pulses

Gollner

Jutas

Kreil

et al. 2022

Advanced Optical Materials

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Next‐generation high‐speed optical networks demand the development of ultrafast optical interconnects capable of Tbit s−1 data rates. By utilizing colloidal CdSe/CdS core/shell quantum dots, gated by intense THz pulses, a proof of concept of an all‐optical femtosecond electro‐absorption switch is presented in this work. Without any additional enhancement of the THz electric field, an extinction contrast of more than 6 dB and transmission changes in the visible of more than 15% are achieved, with the latter setting a new record for solution‐processed electro‐absorption materials at room temperature. The absence of physical artifacts, originating from electrodes and field enhancing structures, allows to employ a simple and intuitive numerical model, which rationalizes the large field‐induced electro‐absorption response. Supported by theoretical calculations, the importance of the energy band alignment of heterostructure quantum dots are discussed for the first time and suggest that further improvement of the modulation depth and contrast may be achieved with Type‐II quantum dots.

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Understanding the features in the ultrafast transient absorption spectra of CdSe quantum dots

Cited by 34 publications

References 30 publications

Atomic fluctuations in electronic materials revealed by dephasing

Atomic fluctuations in electronic materials revealed by dephasing

Applications of ultrafast multidimensional electronic spectroscopy to the study of plant light harvesting systems and colloidal quantum dots

Ultrafast Electro‐Absorption Switching in Colloidal CdSe/CdS Core/Shell Quantum Dots Driven by Intense THz Pulses

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