Unusual vibronic fine structures of the ∼3.0 eV violet emission from ion-implanted ZnO nanorods have been investigated by photoluminescence (PL). A set of equally separated peaks with energy spacing of 72 meV, which corresponds to the longitudinal optical (LO) phonon energy of ZnO, were well resolved in the low-temperature PL spectra. The overall emission band can be perfectly described on the basis of the LO phonon-assisted transition with the Huang–Rhys factor of 1.98, indicating intermediate electron-phonon coupling. The thermal quenching of PL gives rise to an activation energy of ∼160 meV, which is attributed to the energy level of acceptor-like defects introduced by implantation.
This work presents positive experimental evidence for the hole traps in ZnO nanorods, which take part in recombination and change the thermal quenching of Cu-related green emission. The evolution of Cu impurity upon annealing, as well as the formation of Cu-related shallow donors with an energy level of ∼0.11 eV are also indicated by temperature-dependent photoluminescence.
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