Excitonic luminescence upconversion in a two-dimensional semiconductor

Aaron M. Jones, Hongyi Yu, John R. Schaibley, Jiaqiang Yan, David G. Mandrus, Takashi Taniguchi, Kenji Watanabe, Hanan Dery, Wang Yao, Xiaodong Xu

Research output: Contribution to journalArticlepeer-review

143 Scopus citations

Abstract

Photon upconversion is an elementary light-matter interaction process in which an absorbed photon is re-emitted at higher frequency after extracting energy from the medium. This phenomenon lies at the heart of optical refrigeration in solids, where upconversion relies on anti-Stokes processes enabled either by rare-earth impurities or exciton-phonon coupling. Here, we demonstrate a luminescence upconversion process from a negatively charged exciton to a neutral exciton resonance in monolayer WSe 2, producing spontaneous anti-Stokes emission with an energy gain of 30 meV. Polarization-resolved measurements find this process to be valley selective, unique to monolayer semiconductors. Since the charged exciton binding energy closely matches the 31 meV A′ 1 optical phonon, we ascribe the spontaneous excitonic anti-Stokes to doubly resonant Raman scattering, where the incident and outgoing photons are in resonance with the charged and neutral excitons, respectively. In addition, we resolve a charged exciton doublet with a 7 meV splitting, probably induced by exchange interactions, and show that anti-Stokes scattering is efficient only when exciting the doublet peak resonant with the phonon, further confirming the excitonic doubly resonant picture.

Original languageEnglish (US)
Pages (from-to)323-327
Number of pages5
JournalNature Physics
Volume12
Issue number4
DOIs
StatePublished - Apr 1 2016
Externally publishedYes

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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