Near-Unity Green Luminescent Hybrid Manganese Halides: Ionothermal Synthesis and White Light-Emitting Diode Applications

Zero-dimensional (0D) Mn2+-based organic–inorganic metal halides (OIMHs) have garnered significant attention in the field of white light-emitting diodes (WLEDs) due to their low toxicity, high photoluminescence quantum yield (PLQY), small full width at half-maximum (fwhm), and good stability. In this study, we report the synthesis and luminescence characterization of six novel 0D Mn2+-based OIMHs with the general formula [R–Ph3P]2MnX4 (where R = −CH3, −C2H5, −C3H5, −Ph, and −CH2Ph; X = Cl/Br), which were fabricated via an environmentally friendly minimal-solvent ionothermal method. All compounds exhibit bright green emission (506–523 nm) under blue light excitation, narrow fwhm (43–48 nm), high color purity (87–94%), and high thermal stability (>280 °C). Notably, [PhCH2–Ph3P]2MnBr2Cl2 achieves a near-unity PLQY of 92.76% under 450 nm excitation, while [C3H5–Ph3P]2MnBr2Cl2 demonstrates an excellent photoluminescence lifetime of 632.89 μs. A WLED was fabricated by combining [PhCH2–Ph3P]2MnBr2Cl2 with a commercial phosphor and a blue GaN chip (λem = 450 nm), yielding a correlated color temperature of 5502 K and CIE 1931 color coordinates of (0.312, 0.317). This work not only establishes a green synthesis pathway for high-performance Mn2+-based luminescent materials but also offers valuable insights into their application in advanced lighting technologies.