Electroluminescent Diodes Based on Manganese(II) Organic/Metallic Composite Emissive Layer: A Gas-Phase Vacuum Evaporation Approach.

Manganese(II)-based materials are promising for photonic applications due to their low cost, low toxicity, and color-tunable emission via crystal field engineering, making them suitable for uses ranging from anticounterfeiting and X-ray imaging to next-generation displays. However, Mn(II)-based electroluminescent devices typically require the preparation of powders or crystals via solution synthesis or high-temperature solid-state methods, followed by secondary processing using solution or vacuum deposition. Herein, we report a "deposition-as-synthesis" strategy that enables the direct fabrication of Mn(II)-based organometallic composite electroluminescent diodes. A red-emitting composite is readily prepared through the vacuum codeposition of 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBI) and manganese(II) bromide (MnBr2). Spectroscopic analysis reveals that the TPBI matrix interacts with MnBr2 to establish an energy-transfer pathway from organic triplet states to Mn(II) ions, thereby sensitizing the characteristic Mn(II) emission. Through device structure optimization to minimize the injection barrier, we achieved a reduced driving voltage of 3.65 V and a peak external quantum efficiency (EQE) of 1.8%, with characteristic Mn(II) emission peaking at 622 nm and CIE coordinates of (0.59, 0.41). This work demonstrates the potential of the gas-phase vacuum evaporation approach (GPVEA) for preparing efficient Mn(II)-based materials and electroluminescent devices.