Light-emitting diodes fabricated from cytochrome c and myoglobin

We have fabricated ITO-insulator-Al junctions using cytochrome c and myoglobin as insulating layers. The junctions act as light-emitting diodes. The electro-luminescence (EL) spectra of these diodes exhibit broad peaks around 530 and 700 nm, and a weak shoulder around 410 nm. These features are consistent with the absorption spectra. Although the reproducibility of the data is quite poor for the current and the EL intensity, the external quantum efficiency obtained from the two quantities are well expressed by a function of the applied voltage. The quantum efficiency almost linearly increases above the applied voltage of 7 V and reaches to ∼1 × 10−7 at V = 14 V for both cytochrome c and myoglobin diodes.