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Optical absorption spectra of ZnO and sodium doped ZnO nanoparticles. The band around 368 nm is due to exciton absorption in ZnO nanoparticles. Inset shows the variation in exciton peak maximum with Na concentration.
Scanning electron microscope (SEM) images of the prepared samples. Morphology of the particles changes from deformed spherical to flowerlike, with increase in Na concentration.
PL spectra of the prepared samples at an excitation wavelength of 330 nm. The band at 377 nm is from exciton recombination, and the broad band at 548 nm is due to deep level trap emission. The variation with Na concentration of (a) band edge exciton peak wavelength and (b) oxygen vacancy peak intensity are shown in the corresponding insets.
Normalized transmittance of sample ZnNa10 as a function of input laser fluence. Filled circles are experimental data points while solid curves are numerical fits for a two-photon induced excited state absorption process, as given by Eqs. (1) and (2).
Values of linear transmission, 2PA coefficient, and ESA absorption cross section for the samples at 532 nm excitation.
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