Synthesis Of The ZnS Nanocrystals With Different Shape And Structure And High Pressure Study For ZnS Nanorods

As a key semiconductor with large band gap, ZnS is potential optical material for short-wavelength laser and other photoelectronic devices. The nanometer scale ZnS with different structures and morphologies also have been attracted much interest because of its unique structure and luminescent properties at room temperature. The synthesis of ZnS nanocrystal with different structures and morphologies and the physical properties, especially the photoluminescence property are still challenging topics in this field. High pressure can change the structure of materials, and thus change the physical properties. It provides us a very powerful tool to study the relations between the structure and physical properties. For ZnS nanorods, there is no report on the structure phase transition and their photoluminescence properties in the field of high pressure.In this work, we have first studied the synthesis of ZnS nanocrystal with different structure and morphology by changing the molar ratio of reactants in the solvothermal process. The synthesis of the ZnS nanosheets with hexagonal-shape in zinc-blende structure is first reported. And the ZnS nanorods with small diameter good crystallization were synthesized. We found that there is strong correlation between the structure and morphology of the ZnS products in the solvothermal process. DAC combination with Raman spectroscopy has been employed to study the structural phase transition of ZnS nanorods under high pressure for the first time. The photoluminescence properties at ambient and hydrostatic pressure effect on the photoluminescence properties also have been studied.In the process of the solvothermal experiment, the molar ratio of the Zn(NO3)2·6H2O and thiourea was changed between 1:1-1:5, and the structure of the products changed from mixture structure with zincblende and wurtzite to zincblende structure and then to wurtzite structure. The morphology of the products changes from the mixture of nanopaticle and nanorods to nanosheets with hexagonal-shape and then to nanorods. The synthesis of the ZnS nanosheets with hexagonal-shape in zincblende structure is first reported, and the nanosheets with size of 20~50nm is good crystallization. When the molar ratio of the Zn(NO3)2·6H2O and thiourea was changed to 1:5, the obtained ZnS nanorods is good crystallization with the average length of more than 500nm and the average ratio of length to diameter is more than 30. The study of the structure and the morphology of the ZnS products indicates that there is strong correlation between the structure and morphology in the solvothermal process. The photoluminescence of the ZnS nanorods and nanosheets wth pure phase has obvious differences. The ZnS nanosheets have a strong emission band at 534nm while nanorods hav two emission bands at 520nm and 578nm. The results show that we can synthesize the ZnS nanorods with different structure and morphology according to the different application in the luminescence properties.We have carried out in situ high pressure measurements for Raman spectroscopy of ZnS nanorods at room temperature. From the discussion, we know that the Rocksalt structure of ZnS appears near 16.7GPa, and the transition pressure is higher than that of the reports. Near 9.3GPa, the full width at half magnitude(FWHM) of the LO mode have changed abruptly, and at same time, the center and the FWHM of the PL emission band changed obviously. So we infer that wurtzite structure maybe transforms to zinc blende structure. Under high pressure, the emission band of the ZnS nanorods shifted to long-wave band. When the pressure is up to 16.7GPa, the PL emission band disappeared. The above discuss on the PL spectra under high pressure indicated that the high pressure can modulate the PL spectra of the ZnS nanorods obviously.