Photoelectron spectroscopy study of the interactions between ErF3 dopants and Alq3 hosts for near-infrared organic light-emitting diodes

The chemical reaction between ErF3 dopant and tris (8-hydroxy quinoline) aluminum (Alq3) host is investigated by photoelectron spectroscopy. In ErF3–Alq3 composite, the Al 2p core level spectrum shows asymmetry and it is fitted into two contributions: one from Al ions in Alq3 (Al-O-C bond) and the other from Al ions in AlF3 (Al-F bond). Quantitative analyses of each component area support the model that a part of Alq3 is reacted with ErF3 and form the new production of Alq3−xFx. The Er 4d binding energy of ErF3 doped Alq3 film is shifted by 1.5 eV with respect to the one in pristine ErF3 film, which reveals there is a charge transfer from organic molecule to Er atom. Besides, the electroluminescent intensity in visible region decreased greatly with the increase of ErF3 dopant, which shows that the energy is transferred from Alq3 exciton to Erq3 luminescence center.