Synthesis and optical properties of nanostructured ZnS and heteronanostructures based on zinc and silver sulfides

ZnS nanopowders have been synthesized by chemical deposition from aqueous solutions of zinc nitrate and sodium sulfide in the presence of sodium citrate or Trilon B. Ag2S/ZnS heteronanostructures have been prepared by co-deposition of zinc and silver sulfides. The size of nanoparticles in the deposited powders has been estimated by X-ray diffraction and transmission electron microscopy. A change in the ratio between the concentrations of reagents in the reaction mixtures made it possible to obtain ZnS nanopowders with an average particle size of 2–10 nm. The size of the nanoparticles in the prepared heteronanostructures is 8–10 nm. The diffuse reflection spectra have been measured and the corresponding absorption spectra of nanostructured ZnS and Ag2S/ZnS heteronanostructures have been analyzed using Tauc plots. The optical band gap Eg of the studied sulfide nanostructures has been estimated. A blue shift of the optical absorption edge and an increase in the Eg values from 3.59 to 3.72 eV are observed with a decrease in the size of ZnS nanoparticles. An increase in the Ag2S content in Ag2S/ZnS heteronanostructures leads to a decrease in the optical band gap. Pulsed cathodoluminescence of nanostructured ZnS and Ag2S/ZnS heteronanostructures have been investigated. It is found that the maxima of the luminescence spectra of nanostructured zinc sulfide are located at about 450 nm. Prepared samples of nanostructured ZnS possess a very short decay time and thanks to this property the prepared ZnS nanostructures can be used as a material for scintillation detectors.