SUMMARYStrontium (Sr) was evaporated on tris (8-quinolinolato) aluminum (Alq) to form an electron injection layer for organic electroluminescence (EL) device. Chemical status of Sr was examined by x-ray photoelectron spectroscopy (XPS). EL devices having the structure of ITO/PVCz:p-TPD/Alq/Sr/Al were prepared and their luminance and lifetime were measured. It was found that EL characteristics could be improved by depositing metallic Sr layer at a deposition rate higher than 0.7 nm/s. XPS analysis showed that Sr interdiffuses into Alq when the Sr thickness exceeds 40 nm, which caused red shift of luminescence spectra by 10 nm.