Influence of molar concentration on structural, morphological, optical and luminescence of polyvinyl alcohol-capped nanostructured ZnS films

Abstract

Nanostructured ZnS films of various molar concentrations have been deposited using chemical bath deposition (CBD) method on glass substrates in the matrix of polyvinyl alcohol (PVA). Structural analysis of the samples with the help of X-ray diffraction (XRD) shows that the films are of cubic phase structure and diffraction peaks shift toward higher diffraction angle with the increase of molar concentration. Crystallite size is obtained using Scherrer’s formula, Williamson–Hall (WH) plot as well as size–strain plot (SSP), and reveals decrease in size with increasing molar concentration. Surface morphology and surface texture of the samples are observed with the help of atomic force microscopy (AFM) and high-resolution transmission electron microcopy (HRTEM) which exhibit the roughly spherical shape of the particles as well as formation of cluster by a large number of ZnS nanoparticles. Observation from selected area electron diffraction (SAED) pattern also confirms the cubic phase of nanostructured ZnS samples. Surface topographic study using scanning electron microscopy (SEM) also shows particle agglomeration forming nanoclusters and energy-dispersive X-ray spectroscopy observation reveals that the films are composed of zinc and sulfur. With the increase of molar concentration, the optical bandgap energy increases whereas the refractive index as well as dielectric constant decrease, and in comparison to ZnS bulk counterpart, the samples are found to be blue-shifted. Samples exhibit blue emission photoluminescence (PL) band and second-order Raman scattering. Fourier-transform infrared (FTIR) technique is utilized to detect the presence of stabilizing agent.