Efficient and Stable Red‐Orange Emission from Polaronic Magnetic Excitons in Mn (II)‐Doped 0D All‐Inorganic Rb₄CdCl₆

Abstract The impact of magnetic coupling effects on the luminescence of 0D (zero‐dimensional) perovskite materials doped with TM (transition metal) ions remains underexplored. This study synthesizes Mn²⁺‐doped 0D Rb₄CdCl₆ halide structures using a solvent‐based method, with Rb⁺ ions systematically arranged around isolated [CdCl₆]⁴⁻ octahedra. The resulting Rb₄Cd_1‐xMn_xCl₆ powder exhibits stable orange‐red luminescence under UV (ultraviolet) excitation, achieving a PLQY (photoluminescence quantum yield) of 88.96%. The parent Rb₄CdCl₆ is non‐luminescent, but doping with Mn²⁺ induces strong luminescence due to combined emissions from d‐d transitions of Mn²⁺, weakly ferromagnetically coupled Mn²⁺ pairs, and STEs (self‐trapped excitons). Characterization via XRD (X‐ray diffraction) and DFT (density functional theory) reveals that Mn²⁺ doping occurs through both substitutional and interstitial processes, facilitating magnetic coupling. Raman spectroscopy identifies strong electron‐phonon coupling at a phonon mode of 112 cm⁻¹, supporting STEs generation. Magnetic property analysis shows significant ferromagnetic coupling between Mn²⁺ pairs and paramagnetic single Mn²⁺ ions, enhancing luminescence. The material demonstrates remarkable structural and thermal stability, positioning Rb₄Cd_1‐xMn_xCl₆ as a promising candidate for optoelectronic applications.