Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5404178 | Journal of Luminescence | 2006 | 5 Pages |
Abstract
In this paper, highly oriented and vertically arranged ZnO nanotubes are prepared on Al2O3 (0 0 0 1) substrate without employing any metal catalysts by plasma-assisted molecular beam epitaxy. The photoluminescence (PL) spectra at room temperature are studied under high excitation densities. Under lower excitation density (<60 kW/cm2), PL spectrum shows that one strong free exciton emission (FE) locates at 3.306 eV. As the excitation density increases up to 200 kW/cm2, a new emission peak (Pn) located at low-energy side of FE is attributed to the spontaneous emission due to an exciton-exciton (Ex-Ex) scattering process from two ground state excitons, where one exciton is recombined by emitting a photon and the other is scattered into the excited states of n=2,3,4â¦â. Under excitation density of 300 kW/cm2, the stimulated emission originating from Ex-Ex scattering is obtained. When the excitation density is above 580 kW/cm2, the emission from electron-hole plasma is observed in low-energy side of the P band and indicates a typical superradiation recombination processes with increasing excitation density.
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Authors
Y.M. Lu, H.W. Liang, D.Z. Shen, Z.Z. Zhang, J.Y. Zhang, D.X. Zhao, Y.C. Liu, X.W. Fan,