skip to main content

DOE PAGESDOE PAGES

Title: Excitonic luminescence upconversion in a two-dimensional semiconductor

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. Furthermore, this phenomenon lies at the heart of optical refrigeration in solids(1), where upconversion relies on anti-Stokes processes enabled either by rare-earth impurities(2) or exciton-phonon coupling(3). We demonstrate a luminescence upconversion process from a negatively charged exciton to a neutral exciton resonance in monolayer WSe2, 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(4). Since the charged exciton binding energy(5) closely matches the 31 meV A(1)' optical phonon(6-9), 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. Additionally, 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.
Authors:
ORCiD logo [1] ;  [2] ;  [1] ;  [3] ;  [3] ;  [4] ; ORCiD logo [4] ;  [5] ; ORCiD logo [2] ; ORCiD logo [6]
  1. Univ. of Washington, Seattle, WA (United States). Dept. of Physics
  2. Univ. of Hong Kong (China). Dept. of Physics and Center of Theoretical and Computational Physics
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division
  4. National Inst. for Materials Science (NIMS), Tsukuba (Japan). Advanced Materials Lab.
  5. Univ. of Rochester, NY (United States). Dept. of Electrical and Computer Engineering
  6. Univ. of Washington, Seattle, WA (United States). Dept. of Physics and Dept. of Materials Science and Engineering
Publication Date:
Grant/Contract Number:
AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Nature Physics
Additional Journal Information:
Journal Volume: 12; Journal Issue: 4; Journal ID: ISSN 1745-2473
Publisher:
Nature Publishing Group (NPG)
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY
OSTI Identifier:
1334437