Suppressing Energy Migration via Antiparallel Spin Alignment in One‐Dimensional Mn²⁺ Halide Magnets with High Luminescence Efficiency

Abstract Photoexcited energy migration is prone to causing luminescence quenching in Mn 2+ luminescent materials, presenting a formidable challenge for optoelectronic applications. Although various strategies and mechanisms have been proposed to mitigate this issue, the role of spin alignment between adjacent Mn 2+ ions has remained largely unexamined. In this study, we have elucidated the influence of spin alignment on energy migration within the one‐dimensional Mn 2+ ‐metal halide compound (CH 3 ) 4 NMnCl 3 (TMMC) through variable‐temperature photoluminescence (PL) and magnetic‐optical spectroscopy. This investigation was conducted with reference to (CH 6 N 3 ) 2 MnCl 4 (GUA) with isolated [Mn 3 Cl 12 ] 6− trimers and Cd 2+ ‐doped TMMC. The spin order in TMMC below approximately 55 K is demonstrated by the disorder‐order transition observed in the temperature‐dependent magnetic susceptibility. This finding is further corroborated by the negligible shift in the temperature‐ and field‐dependent emission peaks, a consequence of magnetic saturation. Our results indicate that the antiparallel spin alignment along the Mn 2+ chain in TMMC effectively suppresses energy migration and multiphonon relaxation, thereby reducing nonradiative transitions and enhancing the photoluminescence quantum yield (PLQY). This research casts new light on the potential for developing high‐performance Mn 2+ ‐doped phosphors for optoelectronic and spin‐photonic applications, offering insights into the manipulation of spin and energy dynamics in these materials.