The CdS, ZnS:Cu and Cu2S/CdS/ZnS nanocrystals were successfully assembled in the polymer networks by ion exchange and adsorption. The structures and properties of these nanocrystals were investigated by UV, transmission electron microscopy (TEM) and X-ray diffraction. The ZnS:Cu nanocrystals were successfully used to fabricate a single layer structure light-emitting diode, and the blue light of electroluminescence was observed at room temperature which has a low turn-on voltage of less than 4 V, For the Cu2S/CdS/ZnS nanocomposites mixed with the non-linear polymer, the photorefractive (PR) effect of these materials was primarily observed. The two-beam coupling experimental data showed that the optical gain reached about 84.6 +/- 6 cm(-1) at the 400 kV/cm electric field.