Soft lattice and strong exciton–phonon coupling have been demonstrated in layered double perovskites (LDPs) recently; therefore, LDPs represents a promising class of compounds as excellent self‐trapped exciton (STE) emitters for applications in solid‐state lighting. However, few LDPs with outstanding STE emissions have been discovered, and their optoelectronic properties are still unclear. Based on the three‐dimensional (3D) Cs2NaInCl6, we synthesized two 2D derivatives (PEA)4NaInCl8:Sb (PEA=phenethylamine) and (PEA)2CsNaInCl7:Sb with monolayer and bilayer inorganic sheets by a combination of dimensional reduction and Sb‐doping. Bright broadband emissions were obtained for the first time under ambient temperature and pressure, with photoluminescence quantum efficiency (PLQE) of 48.7 % (monolayer) and 29.3 % (bilayer), superior to current known LDPs. Spectroscopic characterizations and first‐principles calculations of excited state indicate the broadband emissions originate from STEs trapped at the introduced [SbCl6]3− octahedron.

Soft lattice and strong exciton-phonon coupling have been demonstrated in layered double perovskites (LDPs) recently; therefore, LDPs represents a promising class of compounds as excellent self-trapped exciton (STE) emitters for applications in solid-state lighting. However, few LDPs with outstanding STE emissions have been discovered, and their optoelectronic properties are still unclear. Based on the threedimensional (3D) Cs 2 NaInCl 6 , we synthesized two 2D derivatives (PEA) 4 NaInCl 8 :Sb (PEA = phenethylamine) and (PEA) 2 CsNaInCl 7 :Sb with monolayer and bilayer inorganic sheets by a combination of dimensional reduction and Sbdoping. Bright broadband emissions were obtained for the first time under ambient temperature and pressure, with photoluminescence quantum efficiency (PLQE) of 48.7 % (monolayer) and 29.3 % (bilayer), superior to current known LDPs. Spectroscopic characterizations and first-principles calculations of excited state indicate the broadband emissions originate from STEs trapped at the introduced [SbCl 6 ] 3À octahedron.

Pressure‐induced emission (PIE) associated with self‐trapping excitons (STEs) in low‐dimensional halide perovskites has attracted great attention for better materials‐by‐design. Here, using 2D layered double perovskite (C6H5CH2CH2NH3+)4AgBiBr8 as a model system, we advance a fundamental physicochemical mechanism of the PIE from the perspective of carrier dynamics and excited‐state behaviors of local lattice distortion. We observed a pressure‐driven STE transformation from dark to bright states, corresponding a strong broadband Stokes‐shifted emission. Further theoretical analysis demonstrated that the suppressed lattice distortion and enhanced electronic dimensionality in the excited‐state play an important role in the formation of stabilized bright STEs, which could manipulate the self‐trapping energy and lattice deformation energy to form an energy barrier between the potential energy curves of ground‐ and excited‐state, and enhance the electron‐hole orbital overlap, respectively.

Herein, we report a novel organic–inorganic hybrid CuI halide PyCs3Cu2Br6 (Py: pyridinium), where pyridinium and cesium ions coexist. We successfully develop a novel strategy for fabricating turn-on responsive materials. PyCs3Cu2Br6 has a higher single-crystal symmetry (no. 191) than its all-inorganic counterpart Cs3Cu2Br5 (no. 62), and the incorporation of organic pyridinium varied the coordination environment of CuI. PyCs3Cu2Br6 formed a triangle planar structure with solely 3-coordinated CuI ions, which quenched its luminescence. However, PyCs3Cu2Br6 presented a hexagonal channel structure, which enabled it with turn-on response upon mechanical force, heat, moisture, and amine vapor. Such structure offered channels for active molecules to diffuse and interact with pyridiniums, leading to the stimuli-triggered phase change to highly emissive Cs3Cu2Br5. To our best knowledge, for the first time, we discover a novel 3-coordinated organic–inorganic hybrid CuI halide with turn-on response to external stimuli. We believe that our study will contribute to expanding the landscape of smart stimulus-responsive materials and lay the foundation for their wide applications.