Photophysics of Direct and Indirect Interlayer Excitons in MoS₂/WS₂ Moiré Superlattices

Understanding the origin of quantum light emission due to the recombination dynamics of interlayer excitons in small-angle twisted van der Waals heterostructures is critical for excitonic science and engineering. However, the origin of all excitonic recombination processes is not well understood. This study investigates the room temperature excitonic dynamics in hBN-encapsulated MoS2/WS2 moiré superlattices. The quantum light due to the interlayer exciton exhibits three recombination components at 1.46 eV (indirect K–Γ), 1.53 eV (indirect Q–Γ), and 1.63 eV (direct K–K). Power-dependent photoluminescence (PL) spectroscopy reveals sublinear behavior for the 1.63 eV peak, suggesting direct interlayer exciton trapping in moiré potentials, while linear responses for the lower energy peaks indicate free indirect excitons. Time-resolved PL analysis, fitted with a biexponential decay, identifies a three-level energy system: (i) a fast decay due to the radiative recombination of bright excitons and (ii) a slow decay due to the momentum-mismatched dark excitons with suppressed radiative rates. A laser power-dependent time-resolved PL study shows phonon-mediated decay dynamics; increasing laser power enhances radiative decay of bright excitons (fast decay accelerates) via phonon scattering, while reduced slow decay reflects saturated phonon populations limiting dark-to-bright state back-conversion. This counterintuitive bright-dark exciton interplay, governed by phonon interactions, highlights the role of moiré trapping and many-body effects. The findings advance the understanding of excitonic behavior at room temperature, critical for designing high-performance excitonic devices such as programmable solid-state quantum emitters and ultrafast optical switches.