ZnO nanobelts are synthesized in high yield by a simple chemical vapor deposition method, at low temperature. And then Au nanoparticles are sputtered on the ZnO nanobelts. The effect on the photoluminescence of Au-ZnO composite nanobelts by surface plasmon is systematically investigated by the scanning electron microscopy, transmission electron microscopy and photoluminescence spectrum. The enhancement ratio by surface plasmon resonance and the almost completely suppressed defect emission for Au-ZnO composite nanobelts are observed, and the emission enhancement ratio η of Au-ZnO composite nanobelts reaches a maximal value of 85-fold. Additionally, the photoluminescence mechanism is proposed in terms of the scattering and absorption by Au nanoparticles, the Purcell enhancement factor, and the Ostwald ripening.
By using a vectorial approach, the validity of paraxial approximation in second harmonic generation (SHG) microscopy under low numerical aperture (NA) is examined when the sample is a collagen fibril Due to the larger value of dzzx and tensorial nature of SHG, the component Ez of the focused field may have strong effect on the radiation pattern of SHG. Numerical results indicate that when the value of NA exceeds 0.3, the effect of Ez can not be neglected, which results in the invalidation of paraxial approximation in SHG microscopy despite the fact that SHG microscopy is still under low NA focusing.
The orientation of the dipole moment, which is one of important parameters in single-molecule fluorescence spectroscopy, is determined by highly focused generalized cylindrical vector beams combined with a confocal far-field microscope. A generalized cylindrical vector beam can be decomposed into a linear superposition of radially polarized and azimuthally polarized components and the ratio of the radial and longitudinal components of the focal electric field can be adjusted by changing the polarization direction. As compared to the case of a radially polarized incident beam, numerical results demonstrate that fluorescence intensity difference among single molecules with different orientations can be effectively overcome for a particular polarization direction of the generalized cylindrical vector beam, which may increases the signal-to-noise ratio of the practical experiments and then ease the difficulty in orientation determination of single molecules.
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