Optoelectronic properties and temperature dependent mechanisms of composite-hydroxide-mediated approach for the synthesis of CdO nanomaterials

Abstract

We report the successful synthesis of polycrystalline CdO nanomaterials at various process temperatures in the range from (180°C - 300°C) by a single step, conventionally simple and cost effective approach. The approach is based on hydroxide melts as solvents and termed as composite-hydroxide-mediated (CHM) approach. The effect of growth temperature on particle nucleation and consequently on the fabrication and purity of CdO nanostructures is investigated for a constant reaction time (24 h). As revealed by x-ray diffraction and Raman spectroscopy, CdO nanostructures can be reproduced in high purity with no traces by varying the synthesis temperature. These nanostructures have random orientations and non-uniform distribution with average crystallite sizes varying from 27 nm down to 7 nm. A study of the optical properties, based on photoluminescence, has demonstrated that emission peaks of CdO nanomaterials are centered at 491 nm and 528 nm which signifies purity of the product from the CHM approach. The direct bandgap determined for CdO (2.49 eV - 2.51 eV) exhibits a blue-shift with process temperature. The photoluminescence peak at 491 nm is attributed to near band-edge emission. Based on experimental results size and morphology manipulation, and possible growth mechanisms for the synthesized product are proposed with CHM at low temperature and without surfactant.