Efficient Emission in Halide Layered Double Perovskites: The Role of Sb3+ Substitution in Cs4Cd1–xMnxBi2Cl12 Phosphors

Layered halide perovskites and double perovskites optoelectronic properties have recently been the subject of intense research. Layered double perovskites represent the merging of both worlds, and as such, have the potential to further expand the already vast space of optoelectronic properties and applications of halide perovskites. Despite having more than 40 known members, to date, only the <111>-oriented layered double perovskites: Cs₄Cd₁–_xMn_xBi₂Cl₁₂, have shown efficient photoluminescence (PL). In this work, we replaced Bi with Sb to further investigate the electronic structure and PL properties of these materials, resulting in two new families of layered inorganic perovskites alloys with full solubility. The first family, Cs₄Cd₁–_xMnSb₂Cl₁₂, exhibits a PL emission at 605 nm ascribed to Mn²⁺ centers in octahedral coordination, and a maximum photoluminescence quantum yield PLQY of 28.5%. The second family of alloys, also with full solubility, Cs₄Cd_0.8Mn_0.2(Sb₁–_yBi_y)₂Cl₁₂, contains a fixed amount of Mn²⁺ and Cd²⁺ cations but different concentrations of the trivalent metals. This variability allows the tuning of the PL emission from 603 nm to 614 nm. We show that the decreased efficiency of the Cs₄Cd₁–_xMn_xSb₂Cl₁₂family compared to Cs₄Cd₁–_xMn_xBi₂Cl₁₂, is mostly due to a decreased spin-orbit coupling in Sb and the subsequent increased electronic delocalization compared to the Bi alloys, reducing the energy transfer to Mn²⁺ centers. This work lays out a roadmap to understand and achieve high photoluminescence efficiencies in layered double perovskites.