Multicolor and near-infrared electroluminescence from the light-emitting devices with rare-earth doped TiO2 films

Abstract

We report on multicolor and near-infrared electroluminescence (EL) from the devices using rare-earth doped TiO2 (TiO2:RE) films as light-emitting layers, which are ascribed to the impact excitation of RE3+ ions, with the EL onset voltages below 10 V. The devices are in the structure of ITO/TiO2:RE/SiO2/Si, in which the SiO2 layer is ∼10 nm thick and RE includes Eu, Er, Tm, Nd, and so on. With sufficiently high positive voltage applied on the ITO electrode, the conduction electrons in Si can tunnel into the conduction band of SiO2 layer via the trap-assisted tunneling mechanism, gaining the potential energy ∼4 eV higher than the conduction band edge of TiO2. Therefore, as the electrons in the SiO2 layer drift into the TiO2:RE layer, they become hot electrons. Such hot electrons impact-excite the RE3+ ions incorporated into the TiO2 host, leading to the characteristic emissions.