Luminescence properties of wurtzite and cubic forms of bulk ZnS have been investigated in detail and compared with that of ZnS nanoparticles. Blue emission observed in both hexagonal and cubic forms of undoped bulk ZnS is explained based on electron-hole recombination involving electron in conduction band and hole trapped in Zn2+ vacancies where as green emission arises due to electron hole recombination from Zn2+ and S2- vacancies. Conversion of wurtzite form to cubic form is associated with relative increase in intensity of green emission due to increased defect concentration brought about by high temperature heat treatment. Copper doping in ZnS, initially leads to formation of both Cu-Zn and Cu-i (interstitial copper) centers, and latter to mainly Cu-Zn centers as revealed by variation in relative intensities of blue and green emission from the samples. (C) 2016 Elsevier Ltd. All rights reserved.