A red‐light emitting europium complex(see Figure) is investigated here as an alternative to traditional fluorescent materials, which have an inherent electroluminescence (EL) efficiency limited to 25 % of their photoluminescence (PL) efficiency. It is shown that by optimizing the structure of Eu complex–based devices significant improvements in the EL efficiency and stability can be obtained.

A variable-temperature reflectance difference spectroscopy study of GaAs grown by molecular beam epitaxy at low-temperature GaAs (LT-GaAs) shows that the Fermi level is mostly determined by the point defects in samples annealed at below 600 °C and can be shifted by photoquenching the defects. The Fermi level is otherwise almost temperature independent, leading to an estimated width of the defect band of 150 meV in the as-grown sample. For LT-GaAs annealed at 850 °C, the Fermi level is firmly pinned, most likely by the As precipitates.