Intraband Relaxation Dynamics of Charge Carriers within CdTe Quantum Wires

Sanderson, William M.; Wang, Fudong; Schrier, Joshua; Buhro, William E.; Loomis, Richard A.

doi:10.1021/acs.jpclett.0c01326

Cited by 3 publications

(31 citation statements)

References 52 publications

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“…Thus, these signals can only be associated with QSR of these states and not by occupancies in these excited levels. As reported elsewhere, 53 the fast shifting is due to contributions from the holes and the slower contributions are from the electrons sampling different quantum-confinement states while relaxing the band edge. These large shifts are not associated with the presence of multiple electron−hole pairs, as described above.…”

Section: ■ Discussionsupporting

confidence: 71%

“…These differences are directly attributed to the contributions from QSR that remain for as long as there are carriers in the QWs. A detailed description of the intraband relaxation dynamics of the charge carriers in the CdTe QWs is reported in ref .…”

Section: Discussionmentioning

confidence: 99%

“…The color scales in parts a and b are in mOD, and the arrows above each panel are the energies of the features identified in the steady-state absorption spectrum. The data in part b were published in a different format in ref .…”

Section: Discussionmentioning

confidence: 99%

“…The small dip in the signal marked with an * is due to scattering of E exc . The data in parts a and b were published in a different format in ref .…”

Section: Calculationsmentioning

confidence: 99%

“…Once the QSR is accounted for, the state-to-state time-dependent shifting of the different spectral features is identified, and the relaxation of the carriers after initial excitation down to the band edge states can be easily identified. While this work focuses on the QSR in CdTe QWs and a simple model for analyzing TA data, the state-to-state intraband relaxation dynamics of the charge carriers characterized using the QSR model were recently reported in ref .…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Photo-Induced State Shifting in 1D Semiconductor Quantum Wires

2020

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We report on the time-dependent, energetic shifting of quantum-confinement states within photoexcited CdTe quantum wires that were identified by using transient absorption (TA) spectroscopy. The initial photoexcitation promotes an electron to states in the conduction band (CB) and generates a hole in the valence band (VB), and the changes in carrier densities give rise to quantum-state renormalization (QSR). This mechanism is akin to the generation of electron and hole polarons that alter the effective masses of the states in the CB and VB that are probed in the TA experiments. Since the energies of the quantum-confinement states are inversely proportional to the effective mass of the carrier, the states undergo QSR that evolves as the carriers relax to the band edge. A simple model is presented which separates the bleach and induced-absorption signals associated with QSR in the TA data from additional bleach signals attributed to the occupancy of carriers in the shifted states. The states are observed to shift independently with time as the carriers relax. The lowest-energy occupancy feature for the CdTe quantum wires shifts from −25 to +3 meV within 600 fs and then to −17 meV on longer time scales after excitation. The Stokes shift of the photoluminescence of the CdTe quantum wires is dominated by the long-time scale QSR of the band-edge states. QSR is likely prominent in other direct-gap semiconductor nanoparticles, especially those with a significant Stokes shift of the photoluminescence from the absorption band-gap transitions.

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Section: ■ Discussionsupporting

confidence: 71%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

“…The small dip in the signal marked with an * is due to scattering of E exc . The data in parts a and b were published in a different format in ref .…”

Section: Calculationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Photo-Induced State Shifting in 1D Semiconductor Quantum Wires

2020

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Facet-Specific Electron Transfer in Pseudo-Two-Dimensional Wurtzite Cadmium Selenide Nanocrystals

Meyer,

Chen,

Loomis

et al. 2023

J. Phys. Chem. C

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Ligand-exchange reactions of wurtzite CdSe quantum platelets (QPs) and quantum belts (QBs) with methyl viologen (MV2+) and the derivative ligands MV2+(CH2) n NH2 (n = 2, 4, or 6) are investigated. The QP and QB photoluminescence is quenched after partial ligand exchange. Spectroscopic and compositional data establish that this initial ligand substitution occurs on the thin QP and QB edges. The MV2+(CH2) n NH2 ligands are shown to be more-efficient photoluminescence quenchers than the parent MV2+ ion. The ligands on the thin, nonpolar, long-edge facets quench the photoluminescence via the trapping of excitons. Transient absorption experiments indicate the excitons dissociate, and electron transfer to the MV2+(CH2) n NH2 ligands only occurs at the polar, short-edge facets of the wurtzite CdSe QPs and QBs. Electron transfer to the MV2+(CH2) n NH2 ligands occurs within 100 fs when exciting at the band edge and on longer time scales, due to intraband relaxation, when exciting at higher energies.

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Dynamic Quantum-State Renormalization and Effects of Competing Pathways on Carrier Relaxation in Semiconductor Nanoparticles

Chen,

Sanderson,

Loomis

2023

J. Phys. Chem. C

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The magnitude and temporal evolution of the quantum-state renormalization (QSR), or the energetic shifting of the quantum-confinement states caused by photoexcitation and changes in electron screening, were probed in transient absorption (TA) spectroscopy measurements of colloidal semiconductor nanoparticles. Experiments were performed on high- and lower-quality wurtzite CdTe quantum wires (QWs) with photoluminescence quantum yields of 8.8% and ∼0.2% using low-excitation fluences. The QSR shifts the spectral features to lower energies in both samples, with larger shifts measured in the high-quality QWs. The TA spectral features measured for both samples shift uniquely with time after photoexcitation, illustrating dynamic QSR that depends on the quantum-confinement states and on the states occupied by carriers. The higher fraction of carriers that reach the band-edge states in the high-quality QWs results in larger renormalization, with the energies of the band-edge states approaching the Stokes shift of the steady-state photoluminescence feature below the band-edge absorption energy. The intraband relaxation dynamics of charge carriers photoexcited in semiconductor nanoparticles was also characterized after accounting for contributions from QSR in the TA data. The intraband relaxation to the band-edge states was slower in the high-quality QWs than in the lower-quality QWs, likely due to the reduced number of trap states accessible. The contrasting relaxation time scales provide definitive evidence for a dependence of the photoluminescence efficiency on excitation energy. These studies reveal the complicated interplay between the energetics and relaxation mechanisms of carriers within semiconductor nanoparticles, even those with the same dimensionality.

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Intraband Relaxation Dynamics of Charge Carriers within CdTe Quantum Wires

Cited by 3 publications

References 52 publications

Photo-Induced State Shifting in 1D Semiconductor Quantum Wires

Photo-Induced State Shifting in 1D Semiconductor Quantum Wires

Facet-Specific Electron Transfer in Pseudo-Two-Dimensional Wurtzite Cadmium Selenide Nanocrystals

Dynamic Quantum-State Renormalization and Effects of Competing Pathways on Carrier Relaxation in Semiconductor Nanoparticles

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