Pseudo‐2D Layered Organic‐Inorganic Manganese Bromide with a Near‐Unity Photoluminescence Quantum Yield for White Light‐Emitting Diode and X‐Ray Scintillator

Eco-friendly lead-free organic-inorganic manganese halides (OIMHs) have attracted considerable attention in various optoelectronic applications because of their superior optical properties and flexible solution processibility. Herein, we report a novel pseudo-2D layered OIMH (MTP)₂ MnBr₄ (MTP: methyltriphenylphosphonium), which exhibits intense green emission under UV/blue or X-ray excitation, with a near-unity photoluminescence quantum yield, high resistance to thermal quenching (I_{150 °C} =84.1 %) and good photochemical stability. These features enable (MTP)₂ MnBr₄ as an efficient green phosphor for blue-converted white light-emitting diodes, demonstrating a commercial-level luminous efficiency of 101 lm W^-1 and a wide color gamut of 116 % NTSC. Moreover, these (MTP)₂ MnBr₄ crystals showcase outstanding X-ray scintillation properties, delivering a light yield of 67000 photon MeV^-1 , a detection limit of 82.4 nGy s^-1 , and a competitive spatial resolution of 6.2 lp mm^-1 for X-ray imaging. This work presents a new avenue for the exploration of eco-friendly luminescent OIMHs towards multifunctional light-emitting applications.