ZnS–Ag2S core–shell nano/hetero-junctions have been synthesized by a two-step co-precipitation technique, in which thin layers of Ag2S have been successfully coated on the surface of ZnS nanospheres. Structural studies and elemental analysis have been performed using X-ray diffraction, Fourier transfer infrared spectroscopy, field emission scanning electron microscopy, energy dispersive spectroscopy, and high-resolution transmission electron microscopy. UV–Vis diffuse reflectance spectroscopy and photoluminescence spectroscopy have been employed to investigate linear optical characteristics. Nanosecond laser pulsed-based single-beam Z-scan analysis has been used to examine the magnitude and the sign of the third-order nonlinear refractive indices. Samples show negative values of nonlinear refractive indices indicating self-defocusing optical nonlinearity under 1064 nm excitation. The results have shown that the third-order nonlinear refractive index in ZnS nanospheres can reach the magnitude of 61.0×10−12m2/W by encapsulating such a nanostructure within nanometer shells of Ag2S. The enhanced nonlinearity for ZnS–Ag2S core–shells has been found to be 9 times higher than sole ZnS nanoparticles, which was estimated to be about 6.4×10−12m2/W.
