Origin of excitonic emission suppression in an individual ZnO nanobelt

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Journal Article
Journal of Physical Chemistry C, 2008, 112 (27), pp. 10095 - 10099
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The near band edge emissions of an individual ZnO nanobelt were investigated by cathodoluminescence spectroscopy, which has unique advantages in higher spatial resolution, orientation, and environmental independence over the conventional photoluminescence spectroscopy. The results show that the presence of a large surface-to-volume ratio is the determinant to suppress the formation of excitons in ZnO nanobelts. Ab initio calculations show that a drastic decrease of density-of-state in the conduction band and increase in the valence band upon size reduction are the key consequence of the large surface-to-volume ratio, revealing the possible fundamental physical origin of exciton suppression. The weak exciton polarity also reduces the likelihood for an exciton to couple with longitudinal phonons. This causes a reduction in the first longitudinal phonon replica intensity and then a complete suppression of the second replica. Understanding the effect of large surface ratio upon the physical properties of ZnO nanomaterials may provide new insights into the fundamental science of nanotechnology for the development of optoelectronics. © 2008 American Chemical Society.
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