Direct Electron Transfer Enables Highly Efficient Dual Emission Modes of Mn 2+ -Doped Cs 2 Na 1- x Ag x BiCl 6 Double Perovskites.

Double perovskites with bright emission, low toxicity, and excellent stability have drawn considerable attention. Herein, we report the hydrothermal synthesis of Mn 2+ -doped Cs 2 Na 1- x Ag x BiCl 6 double perovskites that exhibit dual emission modes. Introducing Ag + ions to Cs 2 NaBiCl 6 samples enables a bright self-trapped exciton (STE) emission in orange-red color, whereas Mn 2+ dopants induce a yellow-orange emission. Importantly, Mn 2+ doping into Cs 2 Na 1- x Ag x BiCl 6 double perovskites with an indirect bandgap enables a high photoluminescence quantum yield of 49.52 ± 2%. Density functional theory calculations reveal that bringing Ag + ions into Cs 2 NaBiCl 6 can localize wave function to the [AgCl 6 ] 5- octahedron and convert dark transitions to bright STE transitions. Moreover, the 3d orbitals of Mn 2+ dopants hybridize with Bi-6p and Cl-3p orbitals at the conduction band minimum, resulting in direct electron transfer from the host to Mn 2+ and a significant increase in photoluminescence efficiency. These results shed light on the optical physical process of Mn 2+ -doped systems, providing useful information for further improvement of the photoluminescence efficiency of double perovskites.