Pressure‐Induced Unusual Transition of Luminescence Mechanics from Self‐Trapped Exciton to Free Exciton Emission in Lead Bromide Perovskitoids

Abstract Understanding the luminescence mechanics of metal halide perovskites is the key to uncovering the detailed pathways responsible for remarkable photophysical properties and engineering materials with enhanced optoelectronic properties. In this work, high pressure is employed to reveal the self‐trapped exciton (STE) emission features of a 1D lead bromide perovskitoid (HM)Pb 2 Br 6 . Upon compression, a remarkable 42‐fold enhancement in the intensity compared to the initial emission, along with exciton transfer from STE emission to narrow free exciton emission, is achieved in (HM)Pb 2 Br 6 . These phenomena are related to the anisotropic compression of (HM)Pb 2 Br 6 , which results in enhanced structural stiffness and a significant reduction in the distances of Pb─Pb bond lengths between inter‐[Pb 2 Br 6 ] 2− chains, as well as Pb─Br bond lengths within the three basic intra‐[Pb 2 Br 6 ] 2− octahedra. These results provide essential insights into the intriguing photophysics of STEs and shed new light on the dramatic exciton transfer to control and enhance the optical properties of the metal halide perovskites.