Coherence Enhancement of Interlayer Excitons Via 3D Trapping

Interlayer excitons (IXs) in van der Waals heterostructures exhibit intrinsically long lifetimes, but disorder-induced inhomogeneous broadening, rapid dephasing, and stacking-dependent emission intensity limit their use in coherent light sources. Here, we integrate robust IXs formed in a two-dimensional perovskite/transition metal dichalcogenide heterostructure, whose emission is largely insensitive to twist angle, into a vertical optical cavity operating in the weak-coupling regime. Quantized momentum-space spectra indicate three-dimensional photonic confinement, which narrows the emission line width from ∼125 to ∼0.75 meV and extends the temporal coherence time from 0.09 to 2.6 ps. IX diffusion over distances comparable to the photonic trap dimensions enables efficient spatial feeding of the confined modes. Time-resolved measurements further reveal Purcell-enhanced recombination of IXs. Our results demonstrate that modulated photonic potentials can enhance the intrinsic emission properties of IXs and provide a route to coherent excitonic light sources based on van der Waals heterostructures.