(a) The cross-section view SEM image of nanowire film. (b) and (c) Typical transmission electron microscopy (TEM) and HRTEM images of a single nanowire, respectively. Inset of (c) shows SAED pattern of the square-enclosed area in (b). (d) Enlarged HRTEM image of the square-enclosed area in (c) showing the planar defects increase the interplanar distance from 0.370 to 0.410 nm. (e) From top to bottom, the Raman spectra of directly prepared nanowires, nanowires and nanowires. (f) Schematic illustration of the structural relaxation around an oxygen vacancy in . The balls connected with four neighboring balls denote tungsten atoms, and the ones connected with two neighboring balls denote oxygen atoms. The increased lengths of W–O bonds around oxygen vacancy are denoted as L.
The PL spectra and their Gauss fitting peaks of nanowires under the excitation of continue wave UV light at 250 (a), 270 (b), and 320 nm (c), respectively, and the schematic illustration (d) of a defect state resonant with the conduction band of nanowires and the relative electronic transitions: represents the optical emission due to the recombination of the electron occupying the defect state and the hole in the top of valence band, while for the band–band transition of nanowires.
(a) The emission intensity spectra of nanowires obtained under the pump intensities of fs laser, correspondingly from low to high, of , , , , , , , , , , and , respectively. (b) The intensity of emission peak vs the pump intensity (the black dot line), the fitting curve of the function of ( is a constant of 6.0), and the fitting curve of the function of ( is a constant of 0.28). (c)–(e) are the emission decay curves of nanowires at low pump intensity of less than (section A), the midst pump density of (section B), and high pump density of more than (section C), respectively.
(a) The UV SF pulse profile recorded under the pump intensity of (the peak of excitation pulse at the time of zero). (b) The time-resolved emission spectra of UV SF just recorded at the time of a, b, c, d, e, and f, which are indicated in (a). (c) The time-integrated spectrum of UV SF. (d) The emission decay curves of UV SF at the center wavelength of 396, 391, and 386 nm: their maximal intensities occur at 4.3, 5.5, and 8.8 ps after the peak of excitation pulse, respectively.
The simplified structural model of a defect plane in the body of a nanowire, showing the oxygen vacancies position themselves regularly in the defect plane.
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