Physicochemical properties of chimie douce derived, digestively ripened, ultra-small (r

Abstract

Ultra-small and uniform sized ZnO quantum dots (QDs) have been synthesized by using a chimie-douce, scalable and eco-friendly method. The physicochemical properties of digestively ripened ZnO QDs have been explored. Uniform sized colloidal QDs are achieved by employing a size control approach called digestive ripening (DR). In DR, monodispersed colloidal nanoparticles are obtained from polydispersed colloidal nanoparticles through the addition of substantial amount of a suitably chosen surfactant (having a suitable ligand). This is performed in the presence of a suitable solvent. Capping with the surfactant (triethanolamine) results in a change in the zeta potential of QDs (increased from 7 ± 3 mV to +22 ± 3 mV) which is responsible for the observed DR and a decrease in particle size from ˜3.5 ± 2 nm to ˜2.8 ± 0.5 nm also noticed. Hard-Soft-Acid-Base surface chemical interactions taking place between ZnO QDs and the surfactant (triethanolamine) are responsible for the formation of digestively ripened ZnO QDs. The as formed ZnO QDs are highly monodispersed in nature and the optical absorption studies indicate that band gap of ZnO QDs found to be Eg˜3.6 eV, indicating strong confinement. The photoluminescence (PL) studies clearly indicates that the major contribution to the photoluminescence is defects present of ZnO QDs-surface and the existence of oxygen vacancy defects on the ZnO QDs-surface are confirmed with PL studies. Time-resolved photoluminescence studies indicate that lifetimes of photo-generated carriers in digestively ripened (DRd) QDs is ˜12 ns and coating with digestive ripening agent reduces the surface-related emission and improves the radiative transitions in DRd ZnO QDs. Spectroscopic studies indicate that formation of highly pure ZnO QDs. These highly monodisperse, stable and ZnO QDs are prospectively useful in contemporary applications such as nanoscale electronic devices and photocatalysis.