Photoluminescence upconversion in monolayer WSe2 activated by plasmonic cavities through resonant excitation of dark excitons

Niclas S. Mueller (), Rakesh Arul, Gyeongwon Kang, Ashley P. Saunders, Amalya C. Johnson, Ana Sánchez-Iglesias, Shu Hu, Lukas A. Jakob, Jonathan Bar-David, Bart Nijs, Luis M. Liz-Marzán, Fang Liu and Jeremy J. Baumberg ()
Additional contact information
Niclas S. Mueller: University of Cambridge
Rakesh Arul: University of Cambridge
Gyeongwon Kang: University of Cambridge
Ashley P. Saunders: Stanford University
Amalya C. Johnson: Stanford University
Ana Sánchez-Iglesias: CIC biomaGUNE, Basque Research and Technology Alliance (BRTA)
Shu Hu: University of Cambridge
Lukas A. Jakob: University of Cambridge
Jonathan Bar-David: University of Cambridge
Bart Nijs: University of Cambridge
Luis M. Liz-Marzán: CIC biomaGUNE, Basque Research and Technology Alliance (BRTA)
Fang Liu: Stanford University
Jeremy J. Baumberg: University of Cambridge

Nature Communications, 2023, vol. 14, issue 1, 1-9

Abstract: Abstract 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 WSe2 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 WSe2 and paves the way for large-area substrates providing nanoscale optical cooling, anti-Stokes lasing, and radiative engineering of excitons.

Date: 2023
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DOI: 10.1038/s41467-023-41401-8

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