Magnetic-fluorescent Fe3O4/ZnS nanocomposites (NCs) with varying concentration of the constituents have been prepared by a simple chemical route. XRD and TEM measurements confirmed the phase purity and crystallinity of the NCs. Thermal analysis shows that the NCs are stable up to about 500 degrees C. Mossbauer analysis reveals that magnetite in the NCs is nonstoichiometric having cation vacancies at the octahedral sites. UV-vis absorption spectra of the NCs show a shift of the absorption peak towards shorter wavelength indicating modification of the band gap of ZnS after formation of the NCs. Photoluminescence emission (PLE) spectra of the NCs display strong near band edge emission (NBE) in the UV region along with moderately strong emission bands in the visible range caused by electronic transitions involving defect-related energy levels in the band gap of ZnS. FTIR and Raman studies confirm presence of only ZnS and Fe3O4 in the NCs. Dc magnetization measurements show a reduction of magnetization value with increase of ZnS content in the NCs. The irreversibility noticed in the ZFC-FC curves has been attributed to the presence of spin-glass like phase in the NCs caused by relaxing spin moments near the surface of Fe3O4 nanoparticles. (C) 2014 Elsevier B.V. All rights reserved.