Synthesis and characterization of ZnS-based luminescent nanostructured semiconductor materials

Full text: The nanostructured materials have been extensively studied, not only because of the new properties and their possible technological applications, but also by the search for a better understanding of the physical and chemical processes that cause these changes. Compared to semiconductor materials, studies of the structure at the nanometer scale has received considerable interest due to the quantum size effect that these materials present. Nanocrystalline semiconductors have intermediate electronic properties between those of molecular structure and macrocrystalline solid, presenting a wide range of applications. Among these materials, zinc sulfide (ZnS) pure or doped has received remarkable attention because of fundamental properties, versatility and potential for several technological applications. However, there is no consensus in the literature about the nature of the photoluminescence emission in various nanocrystalline semiconductor materials. In this context, this work aimed perform the synthesis and the characterization of these nanostructured semiconductor materials and to correlate with photoluminescent properties. As chemical methods of preparation have been successfully used in order to synthesize nanostructured materials, the solvothermal method assisted by microwave was used to prepare ZnS samples. The characterization using X-ray diffraction presents no spurious phases and the typical hexagonal structure for ZnS samples. Moreover, this technique reveals broad diffraction peaks which is characteristic of nanostructured systems. This assertion is confirmed by scanning electron microscopy for ZnS samples in different temperatures of calcination. The micrographs presents agglomerated particles with grain size of ~ 100 nm which increases as the temperature of calcination increases. Photoluminescence measurements presents a emission centered in ~ 523 nm. As the temperature of calcination increases, the center of emission shifts toward lower wave lengths, which has been related to the decrease of defects at the ZnS structure. A correlation between the source of defects and the photoluminescence properties is presented in this work. (author)