One-Dimensional Indium(III) Halide Double Perovskites (CH3NH3)2NaInX6 (X = Cl, Br) and Their Antimony(III)-Induced High Photoluminescence

Low-dimensional In(III) halide perovskites have become one of the most attractive classes of light-emitting materials due to their tunable and high photoluminescence efficiency. However, their synthesis is still a challenge. Here, we report two novel Na(I)–In(III) halide double perovskite-related compounds (MA)2NaInCl6 and (MA)2NaInBr6 and their Sb3+-doped counterparts. Both compounds crystallize in one-dimensional (1D) face-sharing chain structures with a trigonal P3̅m1 symmetry. (MA)2NaInCl6 and (MA)2NaInBr6 show wide and direct band gaps of 5.3 and 3.9 eV, respectively. While both materials are nonemissive in their pristine forms, 5% Sb3+-doped (MA)2NaInCl6 and (MA)2NaInBr6 show green (555 nm) and yellow (585 nm) emission with the photoluminescence quantum yields of 13.8 and 53.6%, respectively. For (MA)2NaInBr6, a PLQY of 67.64% was achieved with 1% Sb doping. Variable-temperature PL studies and density functional theory calculations indicate that the Sb3+ ion introduces self-trapped excitonic (STE) states, which are responsible for the high-efficiency PL emission. Our findings significantly expand the scope of halide double perovskites to low-dimensional photoluminescent In(III)-based metal halide perovskites.