Observation of exciton–phonon coupling and enhanced photoluminescence emission in ZnO nanotwins synthesized by a simple wet chemical approach

Twinned ZnO nanorods with wurtzite structure have been prepared by a simple wet chemical approach at room temperature (RT). The as-synthesized and annealed (at 200 °C for 2 h) samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), UV–visible (UV–vis) absorption and photoluminescence (PL) spectroflourimeters. XRD data shows that Zinc hydroxide is present in RT sample and transformed to wurtzite ZnO structure after thermal annealing. It is found from the observations in SEM that both samples are consisting of twined nanorods in which two nanorods are attached upon each other along the polar surface. The lengths of the lower portion of the twin nanorods are greater than that of the upper portions for both samples. The existence of free exciton and exciton longitudinal optical phonon (LO) coupling at RT have been confirmed from the absorption as well as in PL emission spectra of as-synthesized RT sample. The annealed sample exhibit intense (almost doubled intensity in compared to that of RT sample) PL emission centered at ∼384 nm.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Room temperature wet-chemical synthesis of uncapped ZnO nanotwinned structure. ► Single crystalline Nanotwins are obtained by using water as reaction medium. ► Free exciton and exciton–phonon coupling are observed at room temperature (RT). ► UV photoluminescence peak of RT sample consists of exciton and its phonon replicas. ► Almost doubled UV PL emission in the annealed sample.