Photoluminescence from 2D Perovskite Single-Crystal Films: Dynamic Coexistence of Excitons and Polaritons

Two-dimensional (2D) Ruddlesden-Popper perovskite films with planar crystal surfaces exhibit high exciton binding energies and strong emission features, making them promising candidates for high-performance photonic and optoelectronic applications. However, their emission mechanisms remain controversial. Here, we report the origin of photoluminescence in 2D perovskite single-crystal films and its thickness-dependent evolution in which uncoupled excitons and self-hybridized polaritons coexist dynamically. Remarkably, the thickness-dependent transition from a bare exciton resonance to a mixture of excitons and self-hybridized polaritons was collectively observed through angle-resolved reflection, transmission, and photoluminescence measurements. Distinct spectral signatures and the relative contributions of excitons and polaritons were addressed along with control over the film thickness and detection angle. Consequently, we reveal the diverse photoluminescence of 2D perovskite films arising from the interplay between uncoupled excitons and self-hybridized polaritons. Our understanding is essential for tuning perovskite emission features and developing advanced perovskite light-emitting devices.