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The momentum-forbidden dark excitons can have a pivotal role in quantum information processing, Bose–Einstein condensation, and light-energy harvesting. Anatase TiO2with an indirect band gap is a prototypical platform to study bright to momentum-forbidden dark exciton transition. Here, we examine, by GW plus the real-time Bethe–Salpeter equation combined with the nonadiabatic molecular dynamics (GW + rtBSE-NAMD), the many-body transition that occurs within 100 fs from the optically excited bright to the strongly bound momentum-forbidden dark excitons in anatase TiO2. Comparing with the single-particle picture in which the exciton transition is considered to occur through electron–phonon scattering, within the GW + rtBSE-NAMD framework, the many-body electron–hole Coulomb interaction activates additional exciton relaxation channels to notably accelerate the exciton transition in competition with other radiative and nonradiative processes. The existence of dark excitons and ultrafast bright–dark exciton transitions sheds insights into applications of anatase TiO2in optoelectronic devices and light-energy harvesting as well as the formation process of dark excitons in semiconductors.
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This content will become publicly available on March 12, 2026
Exciton Fine Structure in Wurtzite Nanorods: Is the Exciton Ground State Always Dark?
Colloidal semiconductor nanorods have demonstrated potential as bright, stable, and polarized light sources. Emission of light in these and other nanocrystals proceeds through recombination of confined electron−hole pairs or excitons with tunable size-dependent resonant frequencies. Usually, their brightness is reduced by the “dark exciton”a nonemissive state into which electron−hole pairs relax before recombining radiatively. Here we analyze the fine structure of exciton states in wurtzite CdSe nanorods and demonstrate that, for cylindrical nanorods of radii less than a critical value of R ∼ 30 Å and aspect ratios larger than ∼5, the exciton ground state is the bright emissive state polarized parallel to the axis of the nanorod.
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- Award ID(s):
- 2100248
- PAR ID:
- 10611180
- Publisher / Repository:
- ACS
- Date Published:
- Journal Name:
- Nano Letters
- Volume:
- 25
- Issue:
- 10
- ISSN:
- 1530-6984
- Page Range / eLocation ID:
- 3891 to 3896
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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