Manganese-Doped, Lead-Free Double Perovskite Nanocrystals for Bright Orange-Red Emission

Lead-free halide perovskite nanocrystals (NCs) have recently attracted attention due to their nontoxicity and stability as alternatives to lead-based perovskite NCs. Here, we report undoped and manganese-doped all-inorganic, lead-free double perovskite (DP) NCs: Cs₂NaIn_xBi_1–xCl₆ (0 < x < 1) and Cs₂NaIn_xBi_1–xCl₆:Mn (0 ≤ x ≤ 1) NCs. Undoped NCs exhibit blue emission. Through doping Mn²⁺ ions into Cs₂NaIn_xBi_1–xCl₆ NCs, we can avoid self-trapped exciton emission and realize bright orange red emission of Mn²⁺ dopants with the highest photoluminescence quantum efficiency of 44.6%. The photoluminescence (PL) is tunable from yellow emission to orange-red emission corresponding to a red shift from 583 to 614 nm with increasing In content. Interestingly, the PL emission of Mn-doped NCs shows a red shift from the bulk size to the nanoscale. The Mn-doped NCs show good stability in air. In addition, we further prove the process of dark self-trapped state-assisted Mn²⁺ emission in DP NCs by ultrafast transient absorption techniques.