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Publication . Article . 2021

Upconversion of Light into Bright Intravalley Excitons via Dark Intervalley Excitons in hBN-Encapsulated WSe2 Monolayers

J. Jadczak; Mikhail M. Glazov; Joanna Kutrowska-Girzycka; J. J. Schindler; J. Debus; Ching-Hwa Ho; Kenji Watanabe; +3 Authors
Open Access
Published: 01 Nov 2021 Journal: ACS Nano, volume 15, pages 19,165-19,174 (issn: 1936-0851, eissn: 1936-086X, Copyright policy )
Publisher: American Chemical Society (ACS)

Semiconducting monolayers of transition-metal dichalcogenides are outstanding platforms to study both electronic and phononic interactions as well as intra- and intervalley excitons and trions. These excitonic complexes are optically either active (bright) or inactive (dark) due to selection rules from spin or momentum conservation. Exploring ways of brightening dark excitons and trions has strongly been pursued in semiconductor physics. Here, we report on a mechanism in which a dark intervalley exciton upconverts light into a bright intravalley exciton in hBN-encapsulated WSe2 monolayers. Excitation spectra of upconverted photoluminescence reveals resonances at energies 34.5 and 46.0 meV below the neutral exciton in the nominal WSe2 transparency range. The required energy gains are theoretically explained by cooling of resident electrons or by exciton scattering with Λ- or K-valley phonons. Accordingly, an elevated temperature and a moderate concentration of resident electrons are necessary for observing the upconversion resonances. The interaction process observed between the inter- and intravalley excitons elucidates the importance of dark excitons for the optics of two-dimensional materials.

Subjects by Vocabulary

Microsoft Academic Graph classification: Photoluminescence Photon upconversion Monolayer Exciton Optoelectronics business.industry business Materials science

arXiv: Condensed Matter::Mesoscopic Systems and Quantum Hall Effect Condensed Matter::Materials Science Condensed Matter::Other Condensed Matter::Quantum Gases Condensed Matter::Strongly Correlated Electrons


General Physics and Astronomy, General Engineering, General Materials Science, Article, inter- and intravalley excitons, electron−phonon interaction, electron−electron interaction, upconversion, photoluminescence, WSe2 monolayer

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ACS Nano
Article . 2021
Providers: PubMed Central