Electroluminescence of intrashell transitions in Eu doped single ZnO nanowires.

Tunable nanoscale light emitters are essential to accomplish future multifunctional optoelectronic nano-devices. Here, we present an approach for achieving red electroluminescence from single ZnO nanowires (NWs) implanted with europium ions. The electroluminescence is emitted mainly from the end facets of ZnO NWs at room temperature under the application of an AC voltage. The corresponding electroluminescence spectrum is attributed to the radiative intrashell transitions of the Eu ions, while contributions from near band edge or deep level emission of the ZnO remain absent. The total intensity of the electroluminescence is linearly proportional to the length of the NWs, whereas there is no clear correlation with other morphology factors of the NW based device such as the diameter. Furthermore, the underlying excitation mechanism of the electroluminescence is proposed as direct-impact excitation of Eu ions by hot electrons in the ZnO NWs.