Structural, optical and dielectric studies of wurtzite-type CdS quantum dots green synthesised using Ocimum sanctum (Tulsi) leaf extract

Subhas Chandra Tudu, Maciej Zubko, Joachim Kusz and Ashis Bhattacharjee

Abstract

Present study reports the synthesis of CdS quantum dots (QDs) using Ocimum sanctum (Tulsi) leaf extract by green chemical method. The as-prepared QDs are characterised by different analytical methods. FTIR analysis indicates that the phytochemicals present in Tulsi leaf extract play an important role in controlling the size of the particle and its morphology. The structural properties and surface morphology studies are carried out by powder XRD and SEM with EDX. PXRD patterns revealed the hexagonal structure (wurtzite) for all CdS QDs. The average crystallite size lies in the range of 3.6–3.0 nm which decreases with the increase of the extract concentration. The lattice parameters of the pure and capped CdS QDs are found to be smaller than that of their bulk analogue. The EDAX study confirms the purity of all the prepared samples. The optical study is done by UV-vis spectroscopy and the particle sizes are estimated by an empirical method, which are in good agreement with those obtained from PXRD analysis. Dielectric constant of the QDs is obtained at room temperature at different frequencies where the frequency dependence is pronounced at the lower frequencies. It is noted that the band gap of the capped CdS QDs systematically increases with the increase of the extract concentration whereas the particles size and dielectric constant of these samples decreases with the increasing amount of the extract.