Boosting Mn ⁴⁺ Luminescence Through Hybrid Single‐Crystal Engineering Suppressing Energy Migration and Defect‐Related Quenching

ABSTRACT Mn 4+ ‑doped fluoride red phosphors are promising for wide‑color‑gamut displays, yet they generally suffer from low external quantum efficiency (EQE), long fluorescence lifetime, and poor film‑forming capability, which collectively limit their application in advanced Mini‐light‐emitting diode (Mini‐LED) backlights. To address these challenges, we rationally extend a single‑crystal engineering strategy to tetramethylammonium (TMA)‐based organic–inorganic hybrid fluorides and successfully synthesize a series of single‐crystal (TMA) 2 XF 6 :Mn 4+ (X = Sn 4+ , Ge 4+ , Ti 4+ ) phosphors via a natural cooling crystallization method. The unique spatial “blocking effect” of the hybrid structure, combined with the defect‑reduction effect enabled by the improved crystal quality, synergistically suppresses non‑radiative relaxation and enhances EQE. As a result, the optimized single‑crystal phosphor (TMA) 2 SnF 6 :Mn 4+ exhibits an internal QE (IQE) of 92.26% and an EQE of 71.13%, outperforming the commercial K 2 SiF 6 :Mn 4+ , while maintaining a short (∼3.78 ms) fluorescence lifetime. Moreover, these single‐crystal hybrids show excellent compatibility with organic matrices, allowing the fabrication of uniform, transparent phosphor films with polydimethylsiloxane (PDMS). A prototype 7‑inch white Mini‑LED backlight assembled with the (TMA) 2 SnF 6 :Mn 4+ ‑based film demonstrates the potential of this material system. This work provides a synergistic crystal‑engineering approach to alleviate the efficiency‐lifetime trade‑off in Mn 4+ ‑activated fluorides and offers a viable design route toward high‑performance luminescent materials for next‑generation displays.