Photoluminescence manipulation of WS2 flakes by an individual Si nanoparticle

Optical manipulation of photoluminescence (PL) emission in 2D materials through nanophotonic structures has attracted a lot of attention. However, it has not been achieved through individual all-dielectric nanoparticles (NPs) so far. Here, we put forward a new hybrid system to manipulate the PL emission, which is composed of an individual Si NP deposited on WS2 flakes of different thicknesses. For monolayer WS2 (1L-WS2), PL quenching accompanied by broadening and redshift is observed when integrated with Si NPs. In contrast, the PL of multilayer WS2 (ML-WS2) is significantly enhanced with the help of Si NPs. The PL manipulation of 1L- and ML-WS2 is attributed to the heating and strain effects due to the presence of Si NPs as well as the interaction between the localized field induced by Si NPs and the exciton dipoles in the WS2 flakes. Based on Mie resonances, Si NPs can be effectively heated up by laser pulses. The localized high temperature and strain enable the 1L-WS2 to transform from a direct to an indirect bandgap, resulting in PL quenching and redshift. On the other hand, the out-of-plane oriented exciton dipoles in ML-WS2 are easier to couple with the resonant optical field in Si NPs than the in-plane oriented exciton dipoles in 1L-WS2, which brings about strong field enhancement in favor of PL emission. The new hybrid system is promising for photodetection and on-chip circuit integration.