Effect of preparation temperature on the structural, optical and electronic properties of co-doped ZnS nanostructures

In the present work, the effect of preparation temperature on the structural, optical and electronic properties of cobalt doped zinc sulfide (Zn0.95Co0.05S) nanostructures have been explored. Zn0.95Co0.05S nanostructures were synthesized at different preparation temperatures (300, 400 and 500 degrees C) using the thermolysis method. All samples resembled a single phase cubic zinc blende structure. Upon raising the preparation temperature, the lattice parameter decreases and the anisotropic nature of the crystallite size of the samples is changed into isotropic nature. Rietveld analysis discloses that cobalt (Co) could be incorporated substitutionally for zinc (Zn) ions with occupancies in good agreement with the value intended for preparation. The major characteristic vibration bands of zinc sulfide (ZnS) were determined using Fourier transforms infrared and slightly increased in the wavenumber upon raising the temperature. Ultraviolet-visible spectroscopy technique reveals an increase in the optical band gap upon increasing temperature from 300 to 400 degrees C, and then it reduces at 500 degrees C. Different defects in the different samples are concluded using the emission colors obtained from the photoluminescence technique. Density function theory calculation was applied to investigate the different electronic and optical parameters of ZnS and Co-doped ZnS with and without oxygen.