Mn 2+ -doped ZnS nanoparticles and Mn2+-doped ZnS nanoparticles coated with a shell of ZnS were prepared in reverse micelles. Mn2+ emission at 580 nm in the coated nanoparticles was seven times stronger than that in the uncoated ones. Ultraviolet light treatment enhanced the luminescence at 580 nm in the uncoated nanoparticles, but led to no luminescence enhancement in the coated ones. Some calculations indicated that Mn2+ ions were not randomly distributed in the particle, but preferred to occupy the sites close to the surface. The experiment results indicated that ZnS shell and UV treatment could block the nonradiative transition paths and led to the enhancement of luminescence.
The nonlinear Thomson backscattering of electrons interacting with a circularly polarized laser pulse is studied by using the single-electron model. By means of theoretical analysis and computer simulation, the influence of the central collision place and the beam waist radius on the spectral characteristics of the scattered light are discussed. It is indicated that the spectrum is nonlinear broadened as a result of redshifting of the Thomson scattered frequency. Only when the central collision point is set at a proper place under the tight focusing situation, can quasi-monochromatic x-rays be generated. Taking into account the requirements for the radiation intensity of scattered light, the optimum situation to generate quasi-monochromatic x-rays is explored. In addition, we find that the spectral and angular distribution of the backscattered light do not vary with azimuth angle.
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