Band-Edge Exciton in CdSe and Other II–VI and III–V Compound Semiconductor Nanocrystals − Revisited

Sercel, Peter C.; Efros, Alexander L.

doi:10.1021/acs.nanolett.8b01980

Cited by 92 publications

(129 citation statements)

References 48 publications

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“…Another possibility to explain the lack of shortening is to consider that the ground exciton is built from a 1S electron and a 1P 3/2 hole instead of a 1S 3/2 hole. 36 The only other possibility to explain the lack of bright-dark mixing is to consider that the exciton fine structure in InP QDs is weakly sensitive to shape anisotropy. In this case, the electron-hole exchange interaction splits the eightfold degenerate band-edge exciton into a fivefold degenerate dark exciton with total angular momentum 2 and a threefold degenerate bright exciton with total angular momentum 1.…”

Section: Discussionmentioning

confidence: 99%

Hyperfine Interactions and Slow Spin Dynamics in Quasi-isotropic InP-based Core/Shell Colloidal Nanocrystals

et al. 2019

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Colloidal InP core/sell nanocrystals are taking over CdSe-based nanocrystals, notably in optoelectronic applications. Despite their use in commercial device such as display screens, the optical properties of InP nanocrystals and especially their relation with the exciton fine structure remains poorly understood. In this work, we show that the magneto-optical properties of ensemble InP-based core/shell nanocrystals investigated in strong magnetic fields up to 30 T are strikingly different compared to other colloidal nanostructures. Notably, the mixing of the lowest spin-forbidden dark exciton state with the nearest spin-allowed bright state does not occur, up to the highest magnetic fields applied. This lack of mixing in ensemble of nanocrystals suggests an anisotropy-tolerance of InP nanocrystals. This striking property allowed us to unveil the slow spin dynamics between Zeeman sublevels (up to 400 ns at 15 T). Furthermore, we show that the unexpected magnetic field-induced lengthening of the dark exciton lifetime results from the hyperfine interaction between the spin of the electron in the dark exciton with the nuclear magnetic moments. Our results demonstrate the richness of the spin physics in InP quantum dots and stress the large potential of InP nanostructures for spin-based applications. KEYWORD:colloidal nanostructure, III-V, hyperfine interaction, dark exciton, high magnetic field

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Section: Discussionmentioning

confidence: 99%

Hyperfine Interactions and Slow Spin Dynamics in Quasi-isotropic InP-based Core/Shell Colloidal Nanocrystals

et al. 2019

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“…25 Note that in these calculations, correctly accounting for the long-range exchange interaction, as described in Reference 41, was necessary to properly model the changes in radiative rate. 54 For the conformations in which we have unbalanced charges, such as those highlighted in green in Page 11 of 20 Nano Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Figure 4a, we would also expect to see a permanent charge from EFM, whether positive or negative. Those conformations that demonstrated an increased radiative rate are the same as those for which we would expect to observe an EFM charge.…”

Section: Acs Paragon Plus Environmentmentioning

confidence: 99%

Explaining the Unusual Photoluminescence of Semiconductor Nanocrystals Doped via Cation Exchange

et al. 2019

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Aliovalent doping of CdSe nanocrystals (NCs) via cation exchange processes has resulted in interesting and novel observations for the optical and electronic properties of the NCs. However, despite over a decade of study, these observations have largely gone unexplained, partially due to an inability to precisely characterize the physical properties of the doped NCs. Here, electrostatic force microscopy was used to determine the static charge on individual, cationdoped CdSe NCs in order to investigate their net charge as a function of added cations. While the NC charge was relatively insensitive to the relative amount of doped cation per NC, there was a remarkable and unexpected correlation between the average NC charge and PL intensity, for all dopant cations introduced. We conclude that the changes in PL intensity, as tracked also by changes in NC charge, are likely a consequence of changes in the NC radiative rate caused by symmetry breaking of the electronic states of the nominally spherical NC due to the Coulombic potential introduced by ionized cations.

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“…Band mixing [17,18,58] for the hole wave functions is not included. The fine structure arising from spin-orbit coupling of the hole wave function and from the crystal field and exchange splitting [17,18,20,21,58,74] is also neglected. As we focus on the short time, sub ps optical response, longer time picosecond relaxation processes such as the electron-phonon coupling [27,46,54,75,76], which is the result of non adiabatic coupling between the electronic and nuclear motion and the coupling to biexcitons, owing to weaker Coulomb interactions and Auger relaxation [30,[33][34][35][36][37], are not included in our model.…”

Section: Materials and Methods: Model Excitonic Hamiltonianmentioning

confidence: 99%

“…Among possible building blocks, isolated CdSe QDs were extensively studied [15][16][17][18][19]. Driven by the possible applications to lasing, sensing, light harvesting, and information processing, they have recently received renewed attention focusing on understanding the role of the fine structure coupling [20][21][22][23][24], electronic and vibrational coherences [25][26][27][28][29][30][31][32] and coupling to biexcitons [30,[33][34][35][36][37], electron transport in arrays [38][39][40][41], and the possibility of engineering ultrafast energy transfer between a donor and an acceptor dot [10,11].…”

Section: Introductionmentioning

confidence: 99%

Coherent Exciton Dynamics in Ensembles of Size-Dispersed CdSe Quantum Dot Dimers Probed via Ultrafast Spectroscopy: A Quantum Computational Study

et al. 2020

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Featured Application: Our results on the quantum electronic dynamics of quantum dots pave the way to several applications in nanoscience. The large density of purely excitonic coherences occurring on a wide range of time scales can be controlled by selecting the mean size of the two quantum dots (QDs) used to build the dimer and adjust to applications, for example, to light harvesting and information-processing devices.Abstract: Interdot coherent excitonic dynamics in nanometric colloidal CdSe quantum dots (QD) dimers lead to interdot charge migration and energy transfer. We show by electronic quantum dynamical simulations that the interdot coherent response to ultrashort fs laser pulses can be characterized by pump-probe transient absorption spectroscopy in spite of the inevitable inherent size dispersion of colloidal QDs. The latter, leading to a broadening of the excitonic bands, induce accidental resonances that actually increase the efficiency of the interdot coupling. The optical electronic response is computed by solving the time-dependent Schrodinger equation including the interaction with the oscillating electric field of the pulses for an ensemble of dimers that differ by their size. The excitonic Hamiltonian of each dimer is parameterized by the QD size and interdot distance, using an effective mass approximation. Local and charge transfer excitons are included in the dimer basis set. By tailoring the QD size, the excitonic bands can be tuned to overlap and thus favor interdot coupling. Computed pump-probe transient absorption maps averaged over the ensemble show that the coherence of excitons in QD dimers that lead to interdot charge migration can survive size disorder and could be observed in fs pump-probe, four-wave mixing, or covariance spectroscopy.

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Band-Edge Exciton in CdSe and Other II–VI and III–V Compound Semiconductor Nanocrystals − Revisited

Cited by 92 publications

References 48 publications

Hyperfine Interactions and Slow Spin Dynamics in Quasi-isotropic InP-based Core/Shell Colloidal Nanocrystals

Hyperfine Interactions and Slow Spin Dynamics in Quasi-isotropic InP-based Core/Shell Colloidal Nanocrystals

Explaining the Unusual Photoluminescence of Semiconductor Nanocrystals Doped via Cation Exchange

Coherent Exciton Dynamics in Ensembles of Size-Dispersed CdSe Quantum Dot Dimers Probed via Ultrafast Spectroscopy: A Quantum Computational Study

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