Quantum Confined\nLuminescence in Two Dimensions

Achieving localized light emission from monolayer two-dimensional\n(2D) transition metal dichalcogenides (TMDs) embedded in the matrix\nof another TMD has been theoretically proposed but not experimentally\nproven. In this study, we used cathodoluminescence performed in a\nscanning transmission electron microscope to unambiguously resolve\nlocalized light emission from 2D monolayer MoSe<sub>2</sub> nanodots\nof varying sizes embedded in a monolayer WSe<sub>2</sub> matrix. We\nobserved that the light emission strongly depends on the nanodot size,\nwherein the emission is dominated by MoSe<sub>2</sub> excitons in\ndots larger than 85 nm and by MoSe<sub>2</sub>/WSe<sub>2</sub> interface\nexcitons below 50 nm. Interestingly, at extremely small dot sizes\n(<10 nm), the electron energy levels in the nanodot become quantized,\nas demonstrated by a striking blue-shift in interface exciton emission,\nthus inducing quantum confined luminescence. These results establish\ncontrollable light emission from spatially confined 2D nanodots, which\nholds potential to be generalized to other 2D systems toward future\nnanophotonic applications.