Investigations of doping induced structural, optical and magnetic properties of Ni doped ZnS diluted magnetic semiconductors

We have synthesized diluted magnetic semiconducting nanoparticles of undoped and Ni doped ZnS, by varying Ni concentration, via chemical co-precipitation technique. The formation of cubic zinc blend structure and the incorporation of Ni into ZnS lattice are confirmed by the X-ray diffraction (XRD) measurements. Rietveld refinement of the structural parameters shows a reasonable GOF value. Transmission electron microscopy result reveals the crystalline nature of the ZnS nanocrystal with an average d-spacing of 3.1 Å and also clarifies that the average particle size of the nanoparticles is in the range of 3–7 nm, which are consistence with the XRD results. UV–visible measurement depicts that the band gap of the Ni doped ZnS nanoparticles is higher than that of bulk ZnS, which is a result of the quantum confinement effect. Room temperature photoluminescence (PL) spectra shows the green emission in Ni doped ZnS nanoparticles, which is the characteristic ³T₂–³A₂ transition of Ni²⁺ ion and also depicts the PL quenching effect at higher Ni concentration. Fourier transform infrared measurements show different stretching and vibrational modes and also show the resonance interactions of the sulphide ions. Raman analysis reveals different phonon modes of ZnS and confirms the defect states. Room temperature magnetic measurements demonstrate the ferromagnetic behavior in undoped ZnS nanoparticles due to the presence of structural defects. Systemic studies on the magnetic properties revels that all the doped ZnS nanoparticles exhibit the carrier mediated ferromagnetism and the saturation magnetization increases with increasing concentration of Ni.