Enhanced Photoluminescence of Colloidal Lead‐Free Double Perovskite Cs₂Ag_1−xNa_xInCl₆ 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 Cs₂Na_0.6Ag_0.4InCl₆ NCs. Then Mn²⁺ doped Cs₂Na_xAg_1−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⁺.