Effect of zinc oxide concentration on the core–shell ZnS/ZnO nanocomposites Anita Jain • Sanjay Panwar • T. W. Kang • Sunil Kumar Received: 30 July 2013 / Accepted: 8 October 2013 / Published online: 26 October 2013 Ó Springer Science+Business Media New York 2013 Abstract In this work, synthesis and characterization of core–shell zinc sulphide (ZnS)/zinc oxide (ZnO) nano- composites has been reported to see the effect of ZnO concentration in core–shell combination. The nascent as well as core–shell nanostructures were prepared by a chemical precipitation method starting with the synthesis of nascent ZnS nanoparticles. The change in morphological and optical properties of core–shell nanoparticles was studied by changing the concentration of ZnO for a fixed amount of ZnS. The nascent ZnS nanoparticles were of 4–6 nm in diameter as seen from TEM, each containing primary crystallites of size 1.8 nm which was estimated from the X-ray diffraction patterns. However, the particle size increases appreciably with the increase in ZnO con- centration leading to the well known ZnO wurtzite phase coated with FCC phase of ZnS. Band gap studies were done by UV–visible spectroscopy and it shows that band gap tunability can be achieved appreciably in case of ZnS/ ZnO core–shell nanostructures by varying the concentra- tion of ZnO. Fourier transform infrared analysis also proves the formation of core–shell nanostructures. Photo- luminescence studies show that emission wavelength blue shifts with the increase in ZnO concentration. These core– shell ZnS/ZnO nanocomposites will be a very suitable material for any type of optoelectronic application as we can control various parameters in this case in comparison to the nascent nanostructures. 1 Introduction It is well known fact that semiconductor inorganic particles with nanoscaled dimensions have attractive photophysical properties [1–3] because of their size dependent behaviour and quantum confinement effects. But in recent years, colloidal semiconductor core–shell nanocrystals or quan- tum dots (QDs) have attracted great scientific and techno- logical interest due to their unique passivating and tunable properties [4]. By choosing a particular core and a shell, their morphological and optical properties can be easily tuned to suit for various applications. Various core–shell nanocomposites have been explored, among which the selection of inorganic materials for core–shell nanocom- posites is one of the most popular strategies to provide dense surface protection in one case and the combination of higher or lower bandgap materials in the other case. For example, passivation of the nanocrystals surface by a thin semiconductor shell not only modify the absorption and emission wavelengths, but can increase the quantum yield up to 50–70 %, e.g., CdSe/ZnS, CdSe/CdS and ZnSe/Zn core/shell structure [5, 6]. With higher band gap energy than that of the core, the ZnS shell didn’t absorb the emission from the core and helped to eliminate the broadband emission of the QDs. ZnO-coated ZnS nano- particles have also been prepared by some groups [7, 8] but their X ray diffraction (XRD) results indicated poor crys- tallinity. Daixun et al. [9] studied the influence of ZnO shell thickness on the luminescence properties of Mn- doped ZnS nanoparticles. A strong increase followed by a gradual decline was observed in the room temperature photoluminescence (PL) spectra with the thickening of the ZnO shell. The photoluminescence excitation (PLE) spec- tra exhibited a blue shift in ZnO-coated ZnS:Mn nano- particles compared with the uncoated ones. A. Jain  S. Panwar Department of Physics, Maharishi Markandeshwar University, Mullana, Ambala 133207, India T. W. Kang  S. Kumar (&) Quantum Functional Semiconductor Research Center, Dongguk University, Seoul 100715, South Korea e-mail: sunilkumar32@gmail.com 123 J Mater Sci: Mater Electron (2013) 24:5147–5154 DOI 10.1007/s10854-013-1537-z