Ferromagnetism in Undoped ZnS and Fe Doped ZnS Quantum Dots Synthesized using Polyethylene Glycol

ZnS and Fe doped ZnS quantum dots were synthesized by homogeneous chemical co-precipitation method using polyethylene glycol as a capping agent. The structural, optical, and magnetic properties of synthesized quantum dots were investigated using x-ray diffraction, transmission electron microscopy, fourier transform infrared spectroscopy, ultraviolet-visible absorption spectroscopy, x-ray photoelectron spectroscopy, and photoluminescence spectroscopy. The x-ray diffraction analysis confirmed the single-phase nature of the nanoparticles with the zinc-blend crystal structure. The average crystallite size was found to decrease with Fe dopant while the lattice constant increased. The mean particle size from the transmission electron microscopy image is found to decrease from 14.7 to 4.4 nm. The ultraviolet-visible absorption spectra shows the blue shift in the bandgap (5.0-5.96 eV) due to the quantum confinement effect. Fourier transform infrared spectra confirmed the formation of zinc sulfide and the substitution of Fe ion in it. The photoluminescence spectra reveal the shift from ultraviolet to violet emission. The vibrating sample magnetometer results depict that the zinc sulfide and Fe-doped zinc sulfides are ferromagnetic. Electron paramagnetic resonance spectrum also confirmed the ferromagnetic nature of zinc sulfide and Fe-doped zinc sulfide samples.