Figure 33 shows the emission spectra at room temperature for pure ZnS, doped-Mn2+ (x=0.10,
higher concentrations modified the unit cell of the host material) ZnS and doped-Mn2+
Fe3O4/ZnS at x=0.20 and x=0.25. The pure ZnS presents an emission band centered at ~396 nm
when excited by 250 nm which can be attributed to the defect-state recombination presented mostly on the surface of the nanocrystal [9]. The doped-Mn2+ ZnS at x=0.10 exhibits an
additional strong orange emission peak around 598 nm which could be ascribed to the wellknown
4T1-6A1 Mn transition of Mn2+ ions suggesting a strong coupling between the Mn
levels and host states [10]. It is well-established that Fe3O4 nanoparticles do not show signs of
any emission peak in the interest region but amusingly, the doped-Mn2+ Fe3O4/ZnS core-shell
heterostructured nanoparticles with different atomic concentrations of dopant species exhibited a
weak and broad emission peak centered at 605 nm (see Figure 34) which indicates that the
growth of a doped-Mn2+ ZnS layer on the surface of core material was successfully done.