Green synthesis of ZnO and Ag- ZnO nanocrystalline materials: Optical band gap engineering and multi-model XRD size–strain investigation.

Green synthesis methods have garnered significant research interest in nanotechnology because of their eco-friendliness, simplicity, and affordability. This simple, contemporary, and efficient protocol was used in this study to synthesize ZnO NPs and Ag-ZnO NCs, utilizing leaf extract of Phanera variegata (orchid) as a reducing and capping agent, while using zinc nitrate hexahydrate and silver nitrate as precursors. The optical and structural properties of the synthesized ZnO NPs and Ag-ZnO NCs were analyzed by using UV–Vis Spectroscopy and X-ray Diffraction (XRD). The optical band gap energy of the synthesized ZnO NPs and Ag-ZnO NCs was estimated to be 2.70–2.96 eV and 2.97–3.13 eV, respectively, from the Tauc plot. The crystal size, dislocation density, lattice strain, and morphology index of the synthesized ZnO NPs and Ag-ZnO NCs were determined by using XRD peak profile analysis. These microstructural parameters were determined using various models, including the Debye-Scherrer model, the linear straight-line method of the Scherrer equation, the Monshi-Scherrer model, the Williamson-Hall (Uniform Deformation Model) model, the Modified Williamson-Hall model, the Halder-Wagner model, and the Size-Strain plot (SSP) method. The Halder-Wagner model and the Size–Strain Plot (SSP) method are considered more reliable and effective than other commonly used methods.