Publications [#222970] of Henry Everitt

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Papers Published
  1. Foreman, John V and Everitt, Henry O and Yang, J and McNicholas, T and Liu, J, Effects of reabsorption and spatial trap distributions on the radiative quantum efficiencies of ZnO, Physical Review B (Condensed Matter and Materials Physics), vol. 81 no. 1 (March, 2010), pp. 115318 [nph-data_query], [doi] .

    Abstract:
    Ultrafast time-resolved photoluminescence spectroscopy following one- and two-photon excitations of ZnO powder is used to gain unprecedented insight into the surprisingly high external quantum efficiency of its ``green'' defect emission band. The role of exciton diffusion, the effects of reabsorption, and the spatial distributions of radiative and nonradiative traps are comparatively elucidated for the ultraviolet excitonic and ``green'' defect emission bands in both unannealed nanometer-sized ZnO powders and annealed micrometer-sized ZnO:Zn powders. We find that the primary mechanism limiting quantum efficiency is surface recombination because of the high density of nonradiative surface traps in these powders. It is found that unannealed ZnO has a high density of bulk nonradiative traps as well, but the annealing process reduces the density of these bulk traps while simultaneously creating a high density of green-emitting defects near the particle surface. The data are discussed in the context of a simple rate equation model that accounts for the quantum efficiencies of both emission bands. The results indicate how defect engineering could improve the efficiency of ultraviolet-excited ZnO:Zn-based white light phosphors.