Dual Blue Emission in Ruddlesden–Popper Lead-Bromide Perovskites Induced by Photon Recycling

Two-dimensional Ruddlesden–Popper perovskites (2D RPPs) have attracted tremendous research interest because of their excellent photoelectric performance and environmental stability. However, a fundamental understanding of the intrinsic fluorescence characteristics is still limited, and the origin of dual-emission peaks in 2D RPPs is under intense debate. In this work, high-quality 2D (BA)₂PbBr₄ single crystals that were synthesized using a novel one-step cooling crystallization method exhibited obvious dual blue emission peaks at 412 and 432 nm under wide-field excitation. Space- and time-resolved photoluminescence (PL) spectra of mechanically exfoliated flakes under one- and two-photon excitation reveal that a single high-energy exciton emission was observed from the excitation spot, which underwent a remarkable redshift after propagation. The results can be well fit by the photon recycling model. Our results confirmed that the PL peak at 412 nm originates from the exciton emission at the excitation spot, while the PL peak at 432 nm was induced by photon recycling and long-range waveguide assisted by total internal reflection. Our findings emphasize the importance of photon recycling in the optical spectrum or the exciton kinetics in 2D layered perovskites. Moreover, the 2D perovskite with inner-plane directional photon recycling and a waveguide effect exhibits great potential in constructing high-performance optoelectronic devices.