Comment on “Photodetection and scintillation characterizations of novel lead-bismuth double perovskite halides” by F. Maddalena et al., J. Mater. Chem. C, 2022, 10, 11266

This Comment re-examines the synthesis of Cs₄PbBi₂X₁₂ (X = Br, I) double perovskites reported by Maddalena et al. (J. Mater. Chem. C, 2022, 10, 11266). Thermodynamic calculations reveal strongly negative decomposition energies, favoring decomposition into products involving Cs₃Bi₂X₉. Experimental X-ray diffraction patterns do not match simulated trigonal Cs₄PbBi₂X₁₂ structures but align with Cs₃Bi₂X₉ phases. Optical bandgaps further coincide with decomposition products Cs₃Bi₂X₉. The combined evidence indicates the synthesized materials are phase mixtures, not the purported double perovskites.