Enhanced Photoluminescence of Colloidal Lead‐Free Double Perovskite Cs2Ag1−xNaxInCl6 Nanocrystals Doped with Manganese

Abstract Lead‐free halide double perovskite Cs 2 AgInCl 6 has attracted great attention due to its highly efficient luminescence and excellent stability. However, the parity forbidden electronic transition limits further applications in lighting and display fields. In this work, Cs 2 AgInCl 6 nanocrystals (NCs) are synthesized by injecting trimethyl chlorosilane into the dissolved precursors at 180 °C and the as‐synthesized Cs 2 AgInCl 6 NCs exhibit a weak orange emission peak at 570 nm with a photoluminescence quantum yield (PLQY) of 1.5%. In order to break the parity forbidden transition, various amounts of Na are alloyed into Cs 2 AgInCl 6 NCs, resulting a peak PLQY of 13.4% in Cs 2 Na 0.6 Ag 0.4 InCl 6 NCs. Then Mn 2+ doped Cs 2 Na x Ag 1− x InCl 6 NCs are synthesized in the same approach, in which the highest PLQY can be enhanced up to 36%. As a result, a redshifted photoluminescence emission peak at 625 nm is observed, which derives from the 4 T 1 → 6 A 1 transition of Mn 2+ that is related to the ultrafast energy transfer from self‐trapped exciton states to the 4 T 1 excited state of Mn 2+ .