Login / Signup

Photoluminescence upconversion in monolayer WSe 2 activated by plasmonic cavities through resonant excitation of dark excitons.

Niclas Sven MuellerRakesh ArulGyeongwon KangAshley P SaundersAmalya C JohnsonAna Sánchez-IglesiasShu HuLukas A JakobJonathan Bar-DavidBart de NijsLuis M Liz-MarzánFang LiuJeremy J Baumberg
Published in: Nature communications (2023)
Anti-Stokes photoluminescence (PL) is light emission at a higher photon energy than the excitation, with applications in optical cooling, bioimaging, lasing, and quantum optics. Here, we show how plasmonic nano-cavities activate anti-Stokes PL in WSe 2 monolayers through resonant excitation of a dark exciton at room temperature. The optical near-fields of the plasmonic cavities excite the out-of-plane transition dipole of the dark exciton, leading to light emission from the bright exciton at higher energy. Through statistical measurements on hundreds of plasmonic cavities, we show that coupling to the dark exciton leads to a near hundred-fold enhancement of the upconverted PL intensity. This is further corroborated by experiments in which the laser excitation wavelength is tuned across the dark exciton. We show that a precise nanoparticle geometry is key for a consistent enhancement, with decahedral nanoparticle shapes providing an efficient PL upconversion. Finally, we demonstrate a selective and reversible switching of the upconverted PL via electrochemical gating. Our work introduces the dark exciton as an excitation channel for anti-Stokes PL in WSe 2 and paves the way for large-area substrates providing nanoscale optical cooling, anti-Stokes lasing, and radiative engineering of excitons.
Keyphrases
  • energy transfer
  • quantum dots
  • room temperature
  • fluorescent probe
  • living cells
  • high speed
  • high resolution
  • ionic liquid
  • gold nanoparticles
  • high intensity
  • molecular dynamics