Studies on structural and optical characterization of Na:ZnS nanocomposites

Abstract

In this work, we report the structural, morphological and optical characterization of pure and sodium (Na) mixed ZnS nanocomposites. The Na:ZnS nanocomposites were synthesized by the co-precipitation method using the Na2SO4. The powder XRD pattern reveals a mixed phase of cubic and hexagonal structure. The crystalline size was found to be ∼6 nm based on the full width at half maximum (FWHM) by using the Debye Scherrer formula. Moreover, the diffraction peaks were shifted towards a higher angle compared to pure ZnS. This can be due to the difference in the ionic radii of Na+ and Zn2+ ions. The SEM images show the spherical shape of nanocomposites. The UV-visible absorption spectra of pure and Na:ZnS show an absorption cut-off wavelength of 278 nm (4.46 eV) compared to bulk band gap of ZnS (3.78 eV). The blue shift can be attributed to the quantum confinement effect. In addition to that, the optical absorption increases with increasing Na concentration. The functional groups are identified by FTIR analysis. The photoluminescence (PL) study reveals the near band edge emission at 468 nm (2.64 eV). The broad and high relative intensity of defect level emission is observed in the lower energy side of the PL spectra. The intensity of luminescence increases with increasing Na concentration due to the radiative recombination process. The Raman spectra show the formation of nanocomposite through change in phonon frequency, structural disorder and width for LO phonon mode. A change of 1.7 cm−1 phonon width suggests the formation of disorder.