Effects of reabsorption and spatial trap distributions on the radiative quantum efficiencies of ZnO
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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. © 2010 The American Physical Society.
Published Version (Please cite this version)10.1103/PhysRevB.81.115318
Publication InfoForeman, JV; Everitt, HO; Yang, J; McNicholas, T; & Liu, J (2010). Effects of reabsorption and spatial trap distributions on the radiative quantum efficiencies of ZnO. Physical Review B - Condensed Matter and Materials Physics, 81(11). pp. 115318. 10.1103/PhysRevB.81.115318. Retrieved from https://hdl.handle.net/10161/3240.
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Adjunct Professor of Physics
Dr. Everitt is one of the Army's chief scientists. He works at the Army's Aviation and Missile RD&E Center at Redstone Arsenal, AL. Through his adjunct appointment in the Duke Physics Department, he leads an active experimental research group in condensed matter physics, nanophotonics, molecular physics, and novel terahertz imaging with colleagues on campus and through an international network of collaborators. Four principal research areas are being pursued: 1) Ultrafast Spectroscopy.
George Barth Geller Distinguished Professor of Chemistry
Dr. Liu’s research interests are focusing on the chemistry and material science of nanoscale materials. Specific topics in his current research program include: Self-assembly of nanostructures; Preparation and chemical functionalization of single walled carbon nanotubes; Developing carbon nanotube based chemical and biological sensors; SPM based fabrication and modification of functional nanostructures.
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