Annealing temperature mediated enhanced photosensitivity in bicone-like and flower-like structures of ZnO synthesized using Co-precipitation method

Abstract

Abstract Samples of two ZnO structures - bicone-like as well as flower-like structures - have been synthesized by co-precipitation method using diethanolamine and diethanolamine with polyethylene glycol as starting materials. Further, the synthesized ZnO samples have been annealed at 400 °C, 600 °C and 800 °C separately. All synthesized samples as well as annealed samples have been characterized using UV–visible spectroscopy, photoluminescence (PL) spectroscopy, field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) technique, high-resolution transmission electron microscopy (HR-TEM), photoconductivity measurement technique and fourier transform infrared spectroscopy (FTIR). UV–visible spectra show absorption edges around 306–311 nm and 374–380 nm. PL spectra of prepared ZnO samples show a sharp and intense UV emission due to high concentration of zinc interstitial defects. XRD patterns confirm that all prepared ZnO samples possess hexagonal wurtzite structure. FE-SEM and HRTEM images show that the as-synthesized samples possess both bicone and flower-like structures, whereas annealed samples possess mostly flower-like structures. Photoconductivity property has been investigated under UV–vis illumination in air and vacuum. The samples annealed at 800 °C show highest photosensitivity as compared to as-synthesized samples and samples annealed at 400 °C and 600 °C. The photosensitivity gets increased with increase in annealing temperature as annealing results in increased concentration of zinc interstitial defects. In air medium, the annealed polymer-mediated ZnO samples show rise and decay curves with sharp rise and decay as compared to non-polymer-mediated ZnO counterparts. The photosensitivity of ZnO samples is improved in vacuum as compared to that in air, which may due to occurrence of carbo-optical reactions as a result of presence of hydrocarbons.