期刊
RADIATION MEASUREMENTS
卷 38, 期 4-6, 页码 501-505出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.radmeas.2004.01.022
关键词
radiative lifetime; oscillator strength; excitons; fast scintillators; ZnO; nanoparticles
Radiative lifetimes of free-atom transitions, scaled by omega(3) for comparison at 368 nm, are not faster than about 6.9 ns. BaF2 core-valence luminescence, scaled in the same way from 220 to 368 nm, corresponds to 4.1 ns. In contrast, excitonic transitions in wide-gap semiconductors display subnanosecond radiative lifetimes, and in particular ZnO has radiative lifetimes measured at 50-300 ps for Ddegrees,X and 400-900 ps for free excitons. The giant oscillator strength corresponding to these lifetimes can be explained by theories developed initially for defect-bound excitons, then quantum wells, and nanoparticles. An exciton is a coherent array of N dipoles, where N is the number of sites covered by coherent translational motion of the exciton. This is not essentially a phenomenon of multiple excitons, but applies as well to single-exciton decay. It differs in that regard from the more familiar Dicke giant dipole of N coherently excited atoms lacking translational periodicity. The phenomenon suggests possibilities for achieving ultrafast scintillators and high light yield. (C) 2004 Elsevier Ltd. All rights reserved.
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