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

Abstract Mn²⁺‐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 Mn²⁺‐doped two‐dimensional (2D) layered HDP PPA₄NaInCl₈ (PPA⁺ = C₆H₅(CH₂)₃NH₃⁺) showing promising photoluminescence properties is reported. The large separation between the adjacent inorganic sheets and the good dissolution of Mn²⁺ in the layered structure endow PPA₄NaInCl₈:Mn²⁺ 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 PPA₄NaInCl₈. An energy transfer process occurs between the singlet excitons from PPA⁺ and Mn²⁺, resulting in tunable emission accompanied by the variation of Mn²⁺ 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.