In this work, we present a comprehensive theoretical and computational investigation of exciton fine structures of WSe2-monolayers, one of the best-known two-dimensional (2D) transition-metal dichalcogenides (TMDs), in various dielectric-layered environments by solving the first-principles-based Bethe–Salpeter equation. While the physical and electronic properties of atomically thin nanomaterials are normally sensitive to the variation of the surrounding environment, our studies reveal that the influence of the dielectric environment on the exciton fine structures of TMD-MLs is surprisingly limited. We point out that the non-locality of Coulomb screening plays a key role in suppressing the dielectric environment factor and drastically shrinking the fine structure splittings between bright exciton (BX) states and various dark-exciton (DX) states of TMD-MLs. The intriguing non-locality of screening in 2D materials can be manifested by the measurable non-linear correlation between the BX-DX splittings and exciton-binding energies by varying the surrounding dielectric environments. The revealed environment-insensitive exciton fine structures of TMD-ML suggest the robustness of prospective dark-exciton-based optoelectronics against the inevitable variation of the inhomogeneous dielectric environment.

We present a theoretical investigation of exciton-mediated Förster resonant energy transfers (FRET’s) from photoexcited quantum dots (QD’s) to transition-metal dichalcogenide monolayers (TMD-ML’s), implemented by the quantum theory of FRET on the base of first-principles-calculated exciton fine structures. With the enhanced electron-hole Coulomb interactions, atomically thin TMD-MLs are shown to serve as an exceptional platform for FRET that are mediated purely by excitons and take full advantage of the superior excitonic properties. Remarkably, the energy-transfer responses of atomically thin TMD-ML’s are shown to be dictated by the momentum-forbidden dark excitons rather than the commonly recognized bright ones. Specifically, the longitudinal dark exciton states following the exchange-driven light-like linear band dispersion play a key role in grading up the efficiency and robustness of FRET of TMD-ML against the inhomogeneity of QD-donor ensembles. With the essential involvement of dark excitons, the FRET responses of TMD-ML’s no longer follow the distance power law as classically predicted and, notably, cannot manifest the dimensionality of the donor-acceptor system.

In this work, we present a comprehensive theoretical and computational investigation of exciton fine structures of WSe2-monolayers, one of the best known two-dimensional (2D) transition-metal dichalcogenides (TMD's), in various dielectric-layer environments by solving the first-principles-based Bethe-Salpeter equation. While the physical and electronic properties of atomically thin nano-materials are normally sensitive to the variation of surrounding environment, our studies reveal that the influence of dielectric environment on the exciton fine structures of TMD-ML’s is surprisingly limited. We point out that the non-locality of Coulomb screening plays a key role to suppress the factor of dielectric environment and drastically shrink the fine structure splittings between bright exciton (BX) states and various dark exciton (DX) states of TMD-ML's.The intriguing non-locality of screening in 2D materials can be manifested by the measurable non-linear correlation between the BX-DX splittings and exciton binding energies with varying the surrounding dielectric environments. The revealed environment-insensitive exciton fine structures of TMD-ML's suggest the robustness of prospective dark-exciton-based opto-electronics against the inevitable variation of inhomogeneous dielectric environment.

We present a theoretical investigation of exciton-mediated Förster resonant energy transfers (FRET’s) from photoexcited quantum dots (QD’s) to transition-metal-dichalcogenide monolayers (TMD-ML’s), implemented by the quantum theory of FRET on the base of first-principles-calculated exciton fine structures. With the enhanced electron-hole Coulomb interactions, atomically thin TMD-ML’s are shown to serve as an exceptional platform for FRET that are mediated purely by excitons and take full advantage of the superior excitonic properties. Remarkably, the energy-transfer responses of atomically thin TMD-ML’s are shown to be dictated by the momentum-forbidden dark excitons rather than the commonly recognized bright ones. Specifically, the longitudinal dark exciton states following the exchange-driven light-like linear band dispersion play a key role in grading up the efficiency and robustness of FRET of TMDML against the inhomogeneity of QD-donor ensembles. With the essential involvement of dark exciton, the FRET responses of TMD-ML’s no longer follow the distance power law as classically predicted and, notably, cannot manifest the dimensionality of the donor-acceptor system.