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Title: Hybrid Bismuth(III)-Halide Double Perovskite-Derived Ferroelastic (Pip)2[KBiBr6] with Excitonic and Bi(III) Luminescence Due to Electronic Confinement Along 1D Inorganic Pillar

Authors: M. N. Rowińska, O. Korolevych, A. Kabański, D. Stefańska, T. J. Bednarchuk, A. Piecha-Bisiorek, A. Gągor*

Journal: Chemistry of Materials

DOI: 10.1021/acs.chemmater.5c01183   

A new hybrid double perovskite, (Pip)₂[KBiBr₆], has been synthesized and comprehensively characterized as a stable and environmentally friendly alternative to lead-based halide materials. The compound consists of one-dimensional [KBiBr₆]^2- chains formed by face-sharing BiBr₆ octahedra and KBr₆ antiprisms, separated by piperidinium (Pip⁺) cations linked through N–H···Br hydrogen bonds. It exhibits a room-temperature order–disorder phase transition (T_c = 300/303 K), accompanied by a symmetry reduction (C2/m → P1̅) and the formation of switchable ferroelastic domains. This transition is driven by the partial ordering of Pip⁺ cations and the reorganization of N–H···Br hydrogen bonds. Dielectric relaxation associated with the dynamics of piperidinium cations is observed down to 200 K. DFT calculations and photoluminescence studies confirm strong electronic confinement along the inorganic chains, and reveal intense violet-blue emission arising from excitonic and Bi(III)-related transitions. The compound features a relatively small optical band gap (E_g = 2.8 eV) and exhibits a unique coupling between its structural, ferroelastic, and optoelectronic properties, making it an attractive model for next-generation functional hybrid materials.