Analysis of blue (BE), green (GE), yellow (YE), and red (RE) emission band in ZnO quantum dots

Abstract

ZnO quantum dots (QDs) are prepared by the green technique of colloidal synthesis. Structural, morphological, and optical properties of ZnO (QDs) were investigated by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Photoluminescence. They were prepared ZnO (QDs) in different crystalline growth temperature ranges ∼60–210 ± 4 °C. Using the Hall-effect, we can measure the concentration of carriers, electronic mobility, and resistivity. The morphology and grain size distribution of ZnO (QDs) were analyzed by SEM. Through XRD studies, the hexagonal phase is identified and the grain size was estimated from Scherer’s method, situated at a range of ∼4.2–6.3 nm. Optical properties were investigated by UV-Vis spectroscopy. In Transmittance ( %T) studies, ZnO (QDs) reached ∼80 %, as well as a relative maximum shift at a range of ∼402–378 nm (∼3.08–3.28 eV). The Normalized Absorbance shows different relative maxima at UV-Vis, associated with VB→CB electronic transition and electronic intra-transitions assigned to intrinsic native crystalline defects located at ∼500–700 nm (∼2.48–1.77 eV), shows that the absorption bands originating from the F0 centers prevail over those of F+0 centers of VO when the intrinsic native crystalline defect concentration is high. The Tauc model was used to determine the optical gap energy of ZnO (QDs) is located at ∼3.08–3.26 eV, an optical phenomenon associated with quantum confinement. Photoluminscence (PL). PL signals show emission bands with different intensities: blue (YB), green (GE), yellow (YE), and red (RE) bands, situated in the Vis-region, and commonly associated with color points produced by vacancies and interstices crystalline. Interface passivation layer deposited onto photo anodes has been proven to be an available way to suppress charge recombination and enhance the power conversion efficiency in quantum dot-sensitized solar cells.