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 (MnBr 2 ). Spectroscopic analysis reveals that the TPBI matrix interacts with MnBr 2 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.