Effect of zinc oxide concentration in fluorescent ZnS:Mn/ZnO core-shell nanostructures

In the present work, we have prepared zinc sulphide (ZnS:Mn)/zinc oxide (ZnO) core-shell nanostructures by a chemical precipitation method and observed the effect of ZnO concentration on the fluorescent nanoparticles. Change in the morphological and optical properties of core-shell nanoparticles have been observed by changing the concentration of ZnO in a core-shell combination with optimum value of Mn to be 1 % in ZnS. The morphological studies have been carried out using X-ray diffraction (XRD) and transmission electron microscopy. It was found that diameter of ZnS:Mn nanoparticles was around 4-7 nm, each containing primary crystallites of size 2.4 nm which was estimated from the XRD patterns. The particle size increases with the increase in ZnO concentration leading to the well-known ZnO wurtzite phase which was coated on the FCC phase of ZnS:Mn. Band gap studies were performed by UV-visible spectroscopy and a red shift in absorption spectra have been observed with the addition of Mn as well as with the capping of ZnO on ZnS:Mn. The formation of core-shell nanostructures have been also confirmed by FTIR analysis. Photoluminescence studies show that emission wavelength is red shifted with the addition of ZnO layer on ZnS:Mn(1 %). These core-shell ZnS:Mn/ZnO nano-composites will be a very suitable material for specific kind of tunable optoelectronic devices.