Surface modification of nanostructured ZnS by femtosecond laser pulsing

The surface modification of nanostructured crystalline ZnS by near-infrared femtosecond laser pulses was investigated. A large area nano-grating array was formed on a ZnS surface, with the period and orientation of the nano-gratings depending on the laser wavelength and polarisation direction of the electric field of the light wave, respectively. The nanostructured ZnS surface exhibited the same crystal structure as the polycrystalline ZnS substrate. The photoluminescence (PL) characteristics of ZnS samples were observed to be different before and after laser irradiation when an excitation wavelength above the band-gap energy of ZnS was used. Two additional luminescence peaks were observed to appear in PL spectrum of nanostructured ZnS relative to that of crystalline ZnS. Then, for an excitation wavelength below the band-gap energy, the PL peaks were almost coincident for the two aforementioned ZnS samples; however, the fluorescence lifetime of the nanostructured ZnS sample (2.33 ns) was notably shorter than that of the ZnS crystal sample (10.87 ns).