Defect-related aspects of Mn-doped ZnS nanorods and morphological changes revealed from positron annihilation spectroscopy

Manganese-doped zinc sulfide (Mn_xZn_1-xS) nanorods were synthesized through solvothermal processes and were characterized by x-ray diffraction and scanning and transmission electron microscopy. Positron lifetime and Doppler broadening measure-ments were carried out on powdered samples with different dopant concentrations. A transformation from hexagonal to cubic structure was observed almost concomitantly with the filling of Zn²⁺ vacancies and/or substitution of Zn²⁺ ions by Mn²⁺ ions. The lifetime of positrons annihilating at the surfaces of nanorods decreased with increase in their diameter during increased doping by Mn²⁺ ions. At concentrations above 20%, pyramid-like coarse crystals of MnS were found coexisting with the ZnS nanostructures. The interior of the nanorods seemed to be free of vacancy-type defects unlike in the case of ZnS nanoparticles.