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(a) 40° tilted view, and (b) the top view FE-SEM images of the well-aligned ZnO nanorod arrays on the ZnO thin film substrate.
(a) X-ray diffraction pattern, and (b) the rocking-curve of the as-synthesized well-aligned ZnO nanorod arrays. The inset shows the rocking curve of the ZnO thin film substrate for comparison.
Time-integrated PL spectra of the ZnO nanorod arrays for different excitation conditions, (a) He–Cd CW laser excitation at 325 nm, and (b) fs pulse laser excitation at 267 nm. A broad emission peak around 377 nm was observed at excitation fluence, and a supernarrow emission of a single lasing mode (peak at 383 nm) was observed at excitation fluence. The inset in (b) shows the excitation fluence dependence of emission intensity at 383 nm, indicating that the threshold of lasing is about .
Time-resolved PL detected at 383 nm from the ZnO nanorod arrays at two excitation fluences. For the excitation fluence below the threshold, a biexponential decay model (solid line) fits well to the experimental data (circle), in which the fast time constant , the slow time constant , and the amplitude of are , 360 ps, and 50%, respectively. When the excitation fluence is higher than the threshold, the transient PL (dot) is dominated by a 30 ps decay process, which is the limit of streak camera time resolution.
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