An Effective Two-Emulsion Approach to the Synthesis of Doped ZnS Crystalline Nanostructures

The controlled, room-temperature synthesis of M-doped (M = Cu-II, Mn-II, Sm-III, Gd-III, or Tb-II) ZnS nanostructures (with an average crystallite size of 5-10 nm) in the confined space of miniemulsion droplets is reported herein and discussed. The adopted synthetic route is a colloidal method, ideally suited to easily achieve small particle size and narrow size distribution. The synthesized functional nanostructures crystallize in the sphalerite lattice, as determined by powder X-ray diffraction. In addition to structural characterization, several complementary techniques, such as X-ray photoelectron spectroscopy, thermogravimetric analysis, differential scanning calorimetry, micro-Raman spectroscopy, inductively coupled plasma mass spectrometry, and Fourier transform infrared spectroscopy were used to determine chemical and physical properties as well as the microstructural features of our products. As far as the morphological aspects of the obtained samples are concerned, they were studied by means of scanning and transmission electron microscopies. Finally, the local structure around dopant ions was unravelled by means of X-ray absorption spectroscopy, in particular through extended X-ray absorption fine structure measurements carried out at the Zn, S, and dopant K or L-3 edges. This information has been complemented with the investigation of the photoluminescence properties.