Fine-tuning of energy gap, FTIR, photoluminescence and photocatalytic behavior of Centella asiatica extract mediated Mn/Mg doped ZnO nanostructure

Mn, Mg two element doped ZnO nanostructure derived from Centella asiatica leaf extract with Mn = 2% and Mg = 0, 2 and 4% were prepared by bio-synthesis method. Hexagonal structure of ZnO was maintained throughout the Mn/Mg doping without any additional phase. The derived XRD intensity ratio ((I-100/I-002) was almost equal to one for Mg = 2% than other samples which signifies the tuning of size and shape towards the spherical size which was confirmed by electron microscopic images. The higher absorbance in UV and visible wavelengths at Mg = 4% is used to improve the light harvesting capacity and should increase the photocatalytic activity of composite samples. The tuning of energy gap by Mg doping is useful for the fabrication of opto-electronic devices. The presence of Zn-O-Mn/Mg local bond is confirmed by Fourier transform infra-red studies. The existing strong ultra-violet emission band and the visible blue and green emission bands were discussed based on electronic transition and intensity of defect centers. The elevated photocatalytic activity at Mg = 4% is due to the reduced energy gap (3.89 eV) than other samples and hence the higher absorption in the visible region and the creation of defect states.