Quantum Confined Luminescence in Two Dimensions

Achieving localized light emission from monolayer two-dimensional (2D) transition metal dichalcogenides (TMDs) embedded in the matrix of another TMD has been theoretically proposed but not experimentally proven. In this study, we used cathodoluminescence performed in a scanning transmission electron microscope to unambiguously resolve localized light emission from 2D monolayer MoSe₂ nanodots of varying sizes embedded in a monolayer WSe₂ matrix. We observed that the light emission strongly depends on the nanodot size, wherein the emission is dominated by MoSe₂ excitons in dots larger than 85 nm and by MoSe₂/WSe₂ interface excitons below 50 nm. Interestingly, at extremely small dot sizes (<10 nm), the electron energy levels in the nanodot become quantized, as demonstrated by a striking blue-shift in interface exciton emission, thus inducing quantum confined luminescence. These results establish controllable light emission from spatially confined 2D nanodots, which holds potential to be generalized to other 2D systems toward future nanophotonic applications.