Geometry-Controlled Excitonic Emission Engineering in Monolayer MoS2 Using Plasmonic Hollow Nanocavities

Abstract: Spectral control of closely spaced excitonic transitions is essential for valleytronic photonics, nanoscale light sources, and wavelength-encoded sensing. In monolayer molybdenum disulfide (MoS2), the A and B excitons are separated by only tens of meV, making spectral engineering both fundamentally important and technologically challenging. Here, we numerically investigate plasmon-enhanced excitonic emission in MoS2 coupled to vertically oriented hollow gold nanocylindrical cavities separated by a dielectric spacer. Finite-difference time-domain simulations combined with a photoluminescence-rate framework allow independent evaluation of excitation enhancement, radiative decay modification, non-radiative quenching, and excitonic charge generation. By tuning the cavity aspect ratio, the localized surface plasmon resonance is aligned with either the A or B excitonic transition, while spacer thickness and refractive index regulate near-field confinement and the local density of optical states. Under optimized conditions, excitation rates reach 4.34-fold enhancement while radiative decay exceeds 40-fold, producing photoluminescence increases of 143.85 and 87.27 times for the A and B excitons. The cavity also redistributes the relative intensities of the excitonic peaks, yielding normalized exciton peak ratios up to 2.4 compared to bare MoS2. These results establish hollow plasmonic nanocavities as a geometry-tunable platform for controlling excitonic emission and charge generation in atomically thin semiconductors.