Pressure‐Engineered Excitons Enable Intensified Narrowband Emission Across Visible Spectrum in Two‐Dimensional Lead Halides

Two‐dimensional (2D) lead halides are promising optoelectronic materials, yet precise control over their exciton dynamics remains challenging. Herein, high pressure is employed to engineer excitonic behavior in 2D PMA 2 PbBr 4 (PMA = C 6 H 5 CH 2 NH 3 + ). Initial compression induces dominant interlayer contraction with minimal intralayer distortion, suppressing electron–phonon coupling and enhancing free exciton (FE) emission with an asymmetric line shape. PMA 2 PbBr 4 shows a visible photoluminescence shift from blue to violet. At higher pressures, pronounced structural distortion promotes the formation of self‐trapped excitons, generating new broadband emission. Building on these findings, halogen substitution is applied to further introduce chemical pressure, enhancing the emission sensitivity to external force. The PMA 2 PbX 4 (X = Br, I) series exhibits widely tunable and intensified FE emission across the visible range, spanning from violet to red‐orange. These findings highlight the potential of 2D lead halides as pressure‐responsive materials, highlighting potential in sensing, information encryption, and anti‐counterfeiting.