Effect of zinc oxide concentration in fluorescent ZnS:Mn/ZnO core–shell nanostructures Anita Jain • Sanjay Panwar • T. W. Kang • H. C. Jeon • Sunil Kumar • R. K. Choubey Received: 23 December 2013 / Accepted: 6 February 2014 Ó Springer Science+Business Media New York 2014 Abstract In the present work, we have prepared zinc sulphide (ZnS:Mn)/zinc oxide (ZnO) core–shell nano- structures by a chemical precipitation method and observed the effect of ZnO concentration on the fluorescent nano- particles. Change in the morphological and optical prop- erties of core–shell nanoparticles have been observed by changing the concentration of ZnO in a core–shell com- bination 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 concen- tration 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. 1 Introduction Core–shell nanostructures exhibit novel properties making them attractive for both experimental and technological point of view. Core shell structures are preferred over nanoparticles because they show modified and improved properties than their single component counterparts or nanoparticles of same size [1–4]. 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. ZnO and ZnS are well-known direct band gap II–VI semicon- ductors, having their potential application in fabricating photonic, optical, and electronic devices [5–7]. The syn- thesis of highly monodispersed ZnO and ZnS nanocrys- tallites have paved the way for numerous spectroscopy studies on the ZnS/ZnO heterostructures from both exper- imental and theoretical points of view. So far, the ZnS/ZnO heterostructures, such as biaxial nanobelt [8], nanoribbons [9], nanotetrapods [10], nanowires (NWs) [11] have been successfully synthesized and studied. Our group has already demonstrated the effect of ZnO on nascent ZnS nanoparticles [12]. Since most of the applications require fluorescent nanostructures therefore studies of core–shell nanostructures with a suitable dopant is also needed. Out of the different dopants, it is well known that the divalent Mn 2? ion is an appropriate dopant for the II–VI group semiconductor materials. Mn 2? doping not only enhance the optical transition efficiency and increase the number of A. Jain  S. Panwar Department of Physics, Maharishi Markandeshwar University, Mullana, Ambala 133207, India T. W. Kang  H. C. Jeon  S. Kumar (&) Quantum Functional Semiconductor Research Center, Dongguk University, Seoul 100715, South Korea e-mail: sunilkumar32@gmail.com R. K. Choubey Department of Applied Physics, Defence Institute of Advanced Technology, Girinagar, Pune 411025, India 123 J Mater Sci: Mater Electron DOI 10.1007/s10854-014-1788-3