Highly efficient emission in lead-free inorganic vacancy-ordered Sb-Bi-alloyed halide quadruple perovskites

Lead-free vacancy-ordered quadruple perovskites have received extensive attention in optoelectronic applications. We study the optical properties and charge-carrier dynamics of Cs4Mn(Bi1-xSbx)2Cl12 (0 ≤ x ≤ 1) quadruple perovskite single crystals (SCs), which exhibit excellent stability and Mn2+-based photoluminescence (PL) emission. The ratio of Bi:Sb has a great influence on PL intensity. As the Bi3+ content increases, the PL quantum yield (PLQY) shows a monotonically increasing trend and enhances by more than 40 times, attributed to larger energy difference between conduction band minimum and 4T1 state of Mn2+ ions, weaker Mn-Mn coupling interaction due to longer Mn···Mn distance and smaller Jahn-Teller distortion, and lower carrier-phonon coupling. Moreover, Cs4Mn(Bi1-xSbx)2Cl12 nanocrystals were synthesized through top-down ultrasonic crushing method. The PL quenching of Cs4MnBi2Cl12 nanocrystals compared to corresponding SCs arises from surface defect trapping. Our work provides an in-depth understanding of Mn2+-based PL mechanism.