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

Abstract Lead‐free halide double perovskite Cs2AgInCl6 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, Cs2AgInCl6 nanocrystals (NCs) are synthesized by injecting trimethyl chlorosilane into the dissolved precursors at 180 °C and the as‐synthesized Cs2AgInCl6 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 Cs2AgInCl6 NCs, resulting a peak PLQY of 13.4% in Cs2Na0.6Ag0.4InCl6 NCs. Then Mn2+ doped Cs2NaxAg1−xInCl6 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 4T1→6A1 transition of Mn2+ that is related to the ultrafast energy transfer from self‐trapped exciton states to the 4T1 excited state of Mn2+.