Lighting Up WS ₂ Nanoparticles on Ag Film via Plasmonic Enhancement and Exciton-Resonant Excitation

The manipulation of photoluminescence (PL) in two-dimensional (2D) materials presents a promising approach for the development of compact and tunable nanoscale light sources. Although monolayer transition metal dichalcogenides (TMDCs) exhibit strong excitonic emission owing to their direct bandgap, multilayer TMDCs generally experience reduced PL efficiency due to their indirect band structure. Here, we demonstrate that nanostructured WS2 deposited on an Ag film exhibits markedly enhanced indirect PL emission, facilitated by metal film-assisted near-field enhancement and exciton-resonant excitation. Through systematic comparison of WS2 nanoparticles on Ag and indium tin oxide (ITO) film under varying excitation wavelengths and powers, we show that the Ag substrate enhances PL intensity via metal film-induced field concentration, which is about 27 times stronger than that on the ITO film with the same excitation condition. Numerical simulations corroborate that the observed enhancement results from the enhancement effects of electric field localization and exciton-resonant absorption. Moreover, high-energy excitation induces additional PL peaks, which are attributed to hot carrier relaxation and direct transition phenomena. These findings provide fundamental insights into exciton dynamics within multilayer TMDC nanostructures and propose a scalable strategy for engineering their optical responses through hybrid platforms, thereby establishing a foundation for future applications in nonlinear optics, quantum photonics, and integrated 2D material-based optoelectronic devices.