On the radiative lifetime of free-moving two-dimensional excitons

Paraskevov, A. V.

doi:10.1016/j.jlumin.2012.06.004

Cited by 4 publications

(3 citation statements)

References 11 publications

(29 reference statements)

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“…For example, T* % 3.6 K, in GaAs quantum well. 30 Therefore, one typically observes the well-known linear dependence of s R (T) / T. However, the S-series emission lines in hBN are attributed to the recombination of Frenkel excitons. [26][27][28][29] The Bohr radius of a Frenkel exciton is expected to be a few lattice constants.…”

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“…26 The four main emission peaks located at 5.771 (S4), 5.799 (S3), 5.869 (S2), and 5.897 (S1) eV were attributed to the four Frenkel class free exciton levels originated from the doubly degenerated dipole-forbidden (dark) and dipole-allowed (bright) exciton states, in which the dark exciton state becomes allowed either due to the spontaneous symmetry breaking caused by energy transfer from bright exciton band as a result of the zero-point vibration of the lattice 27,28 or a strong spin-orbital interaction due to 2D layered structure. 29 For 2D excitons, Paraskevov 30 suggests that because of the momentum conservation light emission resulting from direct exciton recombination in directions other than that of in-plane is induced by the exciton-acoustic phonon interaction. Based on this concept, the dependence of the exciton radiative lifetime s R on the effective temperature of the exciton system was derived.…”

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Two-dimensional excitons in three-dimensional hexagonal boron nitride

Cao

Clubine

Edgar

et al. 2013

Applied Physics Letters

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The recombination processes of excitons in hexagonal boron nitride (hBN) have been probed using time-resolved photoluminescence. It was found that the theory for two-dimensional (2D) exciton recombination describes well the exciton dynamics in three-dimensional hBN. The exciton Bohr radius and binding energy deduced from the temperature dependent exciton recombination lifetime is around 8 Å and 740 meV, respectively. The effective masses of electrons and holes in 2D hBN deduced from the generalized relativistic dispersion relation of 2D systems are 0.54mo, which are remarkably consistent with the exciton reduced mass deduced from the experimental data. Our results illustrate that hBN represents an ideal platform to study the 2D optical properties as well as the relativistic properties of particles in a condensed matter system.

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Two-dimensional excitons in three-dimensional hexagonal boron nitride

Cao

Clubine

Edgar

et al. 2013

Applied Physics Letters

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“…Time resolved photoluminescence (PL) measurements on the other hand would rely on the exciton-trion energy eigenstates to relax down to the light cone before they can recombine radiatively with high efficiency [32]. This relaxation process is generally bottlenecked by phonon scattering times which are usually much slower (around a few picoseconds) than the radiative lifetimes inside the light cone [33][34][35][36]. In addition, as discussed in this paper, PL collected from both peaks in the emission/absorption spectra of doped 2D materials are from states that are superpositions of exciton and trion states and contribute to PL from both inside and outside the light cone.…”

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Many-body theory of radiative lifetimes of exciton-trion superposition states in doped two-dimensional materials

Rana,

Koksal,

Jung

et al. 2020

Preprint

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Optical absorption and emission spectra of doped two-dimensional (2D) materials exhibit sharp peaks that are often identified with pure excitons and pure trions (or charged excitons), but both peaks have been recently attributed to superpositions of 2-body exciton and 4-body trion states and correspond to the approximate energy eigenstates in doped 2D materials. In this paper, we present the radiative lifetimes of these exciton-trion superposition energy eigenstates using a many-body formalism that is appropriate given the many-body nature of the strongly coupled exciton and trion states in doped 2D materials. Whereas the exciton component of these superposition eigenstates are optically coupled to the material ground state, and can emit a photon and decay into the material ground state provided the momentum of the eigenstate is within the light cone, the trion component is optically coupled only to the excited states of the material and can emit a photon even when the momentum of the eigenstate is outside the light cone. In an electron-doped 2D material, when a 4-body trion state with momentum outside the light cone recombines radiatively, and a photon is emitted with a momentum inside the light cone, the excess momentum is taken by an electron-hole pair left behind in the conduction band. The radiative lifetimes of the exciton-trion superposition states, with momenta inside the light cone, are found to be in the few hundred femtoseconds to a few picoseconds range and are strong functions of the doping density. The radiative lifetimes of excitontrion superposition states, with momenta outside the light cone, are in the few hundred picoseconds to a few nanoseconds range and are again strongly dependent on the doping density. The doping density dependence of the radiative lifetimes of the two peaks in the optical emission spectra follows the doping density dependence of the spectral weights of the same two peaks observed in the optical absorption spectra as both have their origins in the Coulomb coupling between the excitons and trions in doped 2D materials.

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