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

Abstract 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 MnBr 4 (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 MnBr 4 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 MnBr 4 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.