The realization of blue electroluminescence with high efficiency and lifetime remains a long-standing hurdle for OLED technology to overcome. Divalent Europium [Europium(II)] complexes offer a fundamentally distinct pathway toward this goal, as their atomic 4f-5d transitions yield single-Gaussian, spectrally pure emission with theoretical 100% exciton utilization and no involvement of fragile organic bonds in the emissive process. However, their true potential has never been fully demonstrated before. In this work, we design a rigid aza-crown europium(II) complex (Eu5NHCrown) that achieves near-unity photoluminescence quantum yield with bright, pure-blue emission. The complex sublimes without decomposition and can be vacuum-deposited into a bottom-emitting, single-host OLED architecture, delivering an external quantum efficiency (EQE) of 20.7% with minimal roll-off (19.3% at 1000 cd m-2 ) and a narrowband electroluminescence with CIE coordinates of (0.12, 0.25). These results reveal the true potential of Eu(II) 4f-5d transitions for high-efficiency blue OLEDs, establishing a molecular design concept that bridges atomic-transition efficiency with the processability of organic materials.
@article{arxiv.2604.06476,
title = {Blue organic light-emitting diodes with over 20% external quantum efficiencies based on Europium(II)-emitters},
author = {Mahmoud Soleimani and Toni Bärschneider and Felix Kaden and Roman Tkachov and Sebastian Schellhammer and Sebastian Reineke and Carsten Rothe},
journal= {arXiv preprint arXiv:2604.06476},
year = {2026}
}
Comments
9 pages, 3 figures, additional supporting information