Doping Mn2+ in a New Layered Halide Double Perovskite PPA4NaInCl8 (PPA+ = C6H5(CH2)3NH3+): Dimensional Reduction Accelerating Mn2+ Dissolution and Separation for Efficient Light Emission

Mn 2+ -activated halide double perovskites (HDPs) are found to show promising luminescent behavior and have great potential for optoelectronic applications. However, such interesting materials hitherto are only limited to compounds with a monotonous three-dimensional structure and show a low photoluminescence quantum yield (PLQY). Herein, an Mn 2+ -doped two-dimensional (2D) layered HDP PPA 4 NaInCl 8 (PPA + = C 6 H 5 (CH 2 ) 3 NH 3 + ) showing promising photoluminescence properties is reported. The large separation between the adjacent inorganic sheets and the good dissolution of Mn 2+ in the layered structure endow PPA 4 NaInCl 8 :Mn 2+ with efficient red emission and a record PLQY of 69.90%. The spectroscopic analyses and density functional theory calculations indicate that the inherent absorption and luminescence stem from the inserted organic cations PPA + in PPA 4 NaInCl 8 . An energy transfer process occurs between the singlet excitons from PPA + and Mn 2+ , resulting in tunable emission accompanied by the variation of Mn 2+ concentration. These results provide several new fundamental insights on doping and doped 2D layered HDPs, which enhances the understanding of structure−property relations in this important family.