Uncovering White Light Emission in Pressure‐Treated Sb‐Doped Double Perovskite by Coherent Optical Phonon

Abstract Single‐component white‐light emitters are ideal for solid‐state lighting applications. Here, the dual‐emission white light in the 3D Cs₂NaInCl₆:0.1 Sb³⁺ crystal is successfully achieved by the high‐pressure treatment strategy. Upon compression, the remarkable self‐trapped exciton (STE) emission enhancement is observed at 20.6 GPa due to the tilting and twisting of inorganic octahedron caused by the phase transition of Cs₂NaInCl₆:0.1 Sb³⁺ crystal. Intriguingly, after undergoing the high‐pressure treatment, in addition to the blue high‐energy emission from the STEs, [SbCl₆]³⁻ exhibits the orange low‐energy emission from STEs, which is ascribed to the remaining local distortion of inorganic octahedron resulting from the presence of residual amorphous phase in the local region upon decompression. Furthermore, coherent phonon generation and density functional theory calculations indicate that the electrons exhibit a strong coupling to A_1g stretch mode and T_2g^In bending mode in Cs₂NaInCl₆:0.1 Sb³⁺. After high‐pressure treatment, the coupling between the electrons and the T_2g^In bending mode disappears, suggesting local octahedral symmetry disruption due to residual amorphous structures induced by high‐pressure treatment. This work unveils the relationship between the electron‐phonon coupling and the STE emission and offers a new strategy to design and synthesize the new single‐component white‐light metal halide perovskites.