Ultrafast Interfacial Charge Transfer and Two‐photon Absorption in Lateral WS 2 /WO 3 ·H 2 O Heterostructure

Two‐dimensional (2D) transition metal dichalcogenides (TMDs) exhibit great potential for nonlinear photonics applications due to their large second‐order nonlinear coefficients and prominent two‐photon absorption effect. However, the ultrafast carrier dynamics under nonlinear excitation, especially the excitation of dark excitons governed by parity selection rules, remain insufficiently understood. In this work, monolayer WS 2 and lateral WS 2 /WO 3 ·H 2 O heterostructures were synthesized via an SC‐CO 2 ‐assisted method, and their carrier dynamics under both one‐photon (365, 500 nm) and two‐photon (820 nm) excitations are systematically explored using transient absorption (TA) spectroscopy, particularly the regulatory role of heterointerfaces in the decay processes. The results reveal that ultrafast interfacial charge separation due to the type‐II band alignment of the heterostructure facilitates hot carriers in overcoming the hot‐phonon bottleneck effect under one‐photon excitation, which also provides a competitive relaxation pathway for dark excitons under two‐photon excitation, thereby effectively modulating the intraband relaxation process from dark to bright excitons. The nonlinear photophysical properties of the 2D heterostructures illuminate potential applications in designing high‐performance nonlinear photonic devices.