Giant exciton oscillator strength and radiatively limited dephasing in two-dimensional platelets

Naeem, Ali; Masia, Francesco; Christodoulou, Sotirios; Moreels, Iwan; Borri, Paola; Langbein, Wolfgang Werner

doi:10.1103/physrevb.91.121302

Cited by 165 publications

(252 citation statements)

References 51 publications

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“…The large exciton binding energy in SL-MoSe 2 leads to a faster lifetime, in the sub-picosecond regime 1,17,35,38 . This situation is similar to the fast radiative lifetimes in the 1 ps range observed in two-dimensional CdSe platelets 32 , which have an exciton binding energy of 100-300 meV. In presence of in-plane disorder, the eigenstates have a finite width in K || , yielding longer minimum radiative lifetimes, as only part of the localized exciton wavefunction is within the radiative cone 39 .…”

Section: Discussionsupporting

confidence: 71%

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Resonantly excited exciton dynamics in two-dimensional MoSe2 monolayers

et al. 2017

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We report on the exciton and trion density dynamics in a single layer of MoSe2, resonantly excited and probed using three-pulse four-wave mixing (FWM), at temperatures from 300 K to 77 K . A multi-exponential third-order response function for amplitude and phase of the heterodyne-detected FWM signal including four decay processes is used to model the data. We provide a consistent interpretation within the intrinsic band structure, not requiring the inclusion of extrinsic effects. We find an exciton radiative lifetime in the sub-picosecond range consistent to what has been recently reported 1 . After the dominating radiative decay, the remaining exciton density, which has been scattered from the initially excited bright radiative state into dark states of different nature by exciton-phonon scattering or disorder scattering, shows a slower dynamics, covering 10ps to 10ns timescales. This includes direct bright transitions with larger in-plane momentum, as well as indirect dark transitions to indirect dark states. We find that exciton-exciton annihilation is not relevant in the observed dynamics, in variance from previous finding under non-resonant excitation. The trion density at 77 K reveals a decay of the order of 1 ps, similar to what is observed for the exciton. After few tens of picoseconds, the trion dynamics resembles the one of the exciton, indicating that trion ionization occurs on this timescale.

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Section: Discussionsupporting

confidence: 71%

“…This setup was used in previous works [30][31][32] , and more details can be found in the supplement of Ref. [32]. For all the data shown in this work, each beam had equal power P .…”

Section: Sample and Experimental Setupmentioning

confidence: 99%

Resonantly excited exciton dynamics in two-dimensional MoSe2 monolayers

et al. 2017

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“…The increase of the radiative lifetime with temperature in a 2D system is related to the giant oscillator strength effect (GOST) in 2D. 5,31,32 A thermal redistribution of the generated excitons leads to a temperature increasing fraction of excitons that cannot decay radiatively since their k-vector is outside the radiative light cone. This phenomenon prolongs the overall decay of the photogenerated excitons with increasing temperature since the out of light cone scattering processes are thermally activated.…”

Section: I(t)mentioning

confidence: 99%

Temperature dependent radiative and non-radiative recombination dynamics in CdSe–CdTe and CdTe–CdSe type II hetero nanoplatelets

Scott

Kickhöfel

Schoeps

et al. 2016

Phys. Chem. Chem. Phys.

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aWe investigate the temperature-dependent decay kinetics of type II CdSe-CdTe and CdTe-CdSe corelateral shell nanoplatelets. From a kinetic analysis of the photoluminescence (PL) decay and a measurement of the temperature dependent quantum yield we deduce the temperature dependence of the non-radiative and radiative lifetimes of hetero nanoplates. In line with the predictions of the giant oscillator strength effect in 2D we observe a strong increase of the radiative lifetime with temperature. This is attributed to an increase of the homogeneous transition linewidth with temperature. Comparing core only and hetero platelets we observe a significant prolongation of the radiative lifetime in type II platelets by two orders in magnitude while the quantum yield is barely affected. In a careful analysis of the PL decay transients we compare different recombination models, including electron hole pairs and exciton decay, being relevant for the applicability of those structures in photonic applications like solar cells or lasers. We conclude that the observed biexponential PL decay behavior in hetero platelets is predominately due to spatially indirect excitons being present at the hetero junction and not ionized e-h pair recombination.

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“…Coulomb correlation is found to play a central role on all these properties. It is also responsible for the super-radiance (or giant oscillator strength) observed in experiments [3,4,6], both in core-only and in heterostructured NPLs.…”

Section: Introductionmentioning

confidence: 99%

“…Since the first CdSe NPLs were synthesized in 2008 [2], intensive research has revealed several promising properties for optical and electronic applications, including flat surfaces with atomic monolayer control of thickness [2][3][4], fast and narrow fluorescent spectrum [3][4][5][6], large exciton and biexciton binding energies [6,7], high intrinsic absorption [8], large two-photon-absorption cross section [9,10], weak coupling of carriers to acoustic phonons [11], fast and efficient fluorescence resonance energy transfer [12], suppressed multiexciton recombination [13], and highly directional emission [14].…”

Section: Introductionmentioning

confidence: 99%

Excitons in core-only, core-shell and core-crown CdSe nanoplatelets: Interplay between in-plane electron-hole correlation, spatial confinement, and dielectric confinement

2017

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Using semianalytical models we calculate the energy, effective Bohr radius, and radiative lifetime of neutral excitons confined in CdSe colloidal nanoplatelets (NPLs). The excitonic properties are largely governed by the electron-hole in-plane correlation, which in NPLs is enhanced by the quasi-two-dimensional motion and the dielectric mismatch with the organic environment. In NPLs with lateral size L 20 nm the exciton behavior is essentially that in a quantum well, with super-radiance leading to exciton lifetimes of 1 ps or less, only limited by the NPL area. However, for L < 20 nm excitons enter an intermediate confinement regime, hence departing from the quantum well behavior. In heterostructured NPLs, a different response is observed for core-shell and core-crown configurations. In the former, the strong vertical confinement limits separation of electrons and holes even for type-II band alignment. The exciton behavior is then similar to that in core-only NPL, albeit with weakened dielectric effects. In the latter, charge separation is also inefficient if band alignment is quasi-type-II (e.g., in CdSe/CdS), because electron-hole interaction drives both carriers into the core. However, it becomes very efficient for type-II alignment, for which we predict exciton lifetimes reaching microseconds.

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Giant exciton oscillator strength and radiatively limited dephasing in two-dimensional platelets

Cited by 165 publications

References 51 publications

Resonantly excited exciton dynamics in two-dimensional MoSe2 monolayers

Resonantly excited exciton dynamics in two-dimensional MoSe2 monolayers

Temperature dependent radiative and non-radiative recombination dynamics in CdSe–CdTe and CdTe–CdSe type II hetero nanoplatelets

Excitons in core-only, core-shell and core-crown CdSe nanoplatelets: Interplay between in-plane electron-hole correlation, spatial confinement, and dielectric confinement

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