Effect of Mn doping on defect-related photoluminescence and nanostructure of dense 3-D nano-root network of ZnO

Abstract

In this paper, we investigate the effect of Mn doping on an interesting morphology of ZnO thin films prepared by sol-gel spin coating technique. The tunability of morphology, structural and optical properties by doping has been reported. X-ray diffraction (XRD) patterns of the samples annealed at 400 °C confirm the formation of hexagonal wurtzite ZnO without any Mn related phases. On introduction of Mn in ZnO lattice, the crystallite size decreases. Field emission scanning electron microscope (FESEM) studies of the samples confirmed the formation of 3-D nanostructured thin films with morphology similar to a dense network of roots. The nano-root network comprises nanoparticles and as the Mn content is increased, the nanoparticles agglomerate. Energy-dispersive X-ray spectroscopy-based color mapping technique was employed to observe the distribution of Zn, Mn, and O elements. On increasing the doping concentration of Mn, there is a blue-shift in the absorption edge in the absorption spectra recorded by UV–Vis spectroscopy. The optical bandgap increases linearly from 3.26 eV to 3.32 eV on increasing the Mn content from 0 at% to 5 at%. Photoluminescence spectroscopy was used to characterize the deep level emissions. A broad deep level emission band arising due to defects was observed which ranges from violet to red region in the undoped ZnO and is significantly suppressed after Mn-doping. Owing to its dense 3-D intertwined nanoroot network, the proposed study is expected to find potential application in gas sensing, photodetection and catalysis.