Three-Photon Luminescence Assisted by Exciton Energy Transfer in Au-WS₂ Hybrid Monolayers

Kuang-I Lin^1,2*, Wei-Bang Li¹, Shiue-Yuan Shiau³, Yung-Huang Chang⁴

¹Core Facility Center, National Cheng Kung University, Tainan, Taiwan
²Academy of Innovative Semiconductor and Sustainable Manufacturing, National Cheng Kung University, Tainan, Taiwan
³Physics Division, National Center for Theoretical Sciences, Taipei, Taiwan
⁴Bachelor program in interdisciplinary studies, National Yunlin University of Science and Technology, Yunlin, Taiwan

* Presenter:Kuang-I Lin, email:kilin@mail.ncku.edu.tw

In this study we use femtosecond laser to excite the WS₂ monolayer decorated with gold (Au) nanoparticles. When we tune the laser photon energy below 1 eV, we observe photoluminescence (PL) signal of green and blue light with energy ranging from 2.4-3.3 eV emitting from the sample. This shows that the associated processes involve at least three photons, as evidence by the pump power dependence. This signal cannot be explained by WS₂ or Au nanoparticles alone, but has to be attributed to the coherent processes of both WS₂ and Au nanoparticles all together. Multiphoton PL excitation microscopy studies reveal that the absorption process begins with a two-photon excitation in WS₂, followed by the exciton resonance energy transfer to the Au nanoparticles. The energy of the exciton then is transformed into an interband excitation (d  sp) in Au nanoparticle, filling the hole created by an intraband process due to a third photon absorbed by Au nanoparticle. Finally, the PL occurs when the sp-band electron refills the hole in the d-band.

Keywords: Transition metal dichalcogenide, Gold nanoparticle, Energy transfer, Three-photon luminescence, Chemical vapor deposition