Auger-type hole trapping process at green emission centers of ZnO Nanowires

The origins of the green emission (GE) from ZnO nanostructures remain highly controversial despite extensive studies. Herein, transient absorption spectroscopy (TAS) revealed a small Stokes shift of ∼180 meV between the GE-centers (located at ∼0.7 eV above the valence band) and the GE peak — yielding the first experimental evidence of the GE originating from charge transitions of the ZnO di-vacancies proposed recently in density functional calculations. TAS also uncovered an ultrafast Auger-type hole-trapping process to V ZnO that occurs in a sub-ps timescale.