Pronounced Photoluminescence Enhancement and Nonmonotonic Bandgap Evolution in 2D Ruddlesden–Popper Perovskites under High Pressure

Pressure-induced optical modulation in two-dimensional Ruddlesden–Popper perovskites is intricately linked to the structural compressibility. Using (001)-oriented IBA2PbI4 single crystals, we combine in situ high-pressure spectroscopy with first-principles calculations to unveil a three-stage bandgap evolution─redshift, blueshift, and subsequent redshift─accompanied by a 20-fold photoluminescence enhancement at 0.58 GPa prior to quenching at 4.7 GPa. This nonmonotonic response originates from a compression-driven crossover from interlayer to intralayer deformation: initial interlayer contraction strengthens intermolecular coupling and suppresses nonradiative losses; intermediate intralayer compression induces octahedral distortion; and further pressurization triggers amorphization. Our findings provide a generalized mechanistic framework for tailoring optical functionalities in layered hybrid perovskites via hydrostatic pressure.