Enhanced photoluminescence of thiolactic acid capped CdS quantum dots by surface engineering using inorganic acid

Abstract

Thiolactic acid capped CdS quantum dots (QDs) were prepared through hydrothermal route. Use of TLA as capping agent eventually enhances the water solubility as well as stability of the CdS QDs. The pendant methyl group connected with the secondary carbon atom of TLA helps to form good linkage with the surface of CdS QDs. Hydrophobic character of methyl group prevents aggregation of QDs in aqueous phase which ultimately results in highly luminescent CdS QDs. Synthesis conditions have been systematically optimized to improve the PL efficiency and noticed that values of pH noticeably changed the optical properties of CdS QDs. Observation has been extended on synthesized QDs to check the effect of pH if any. It has been found that the photoluminescence quantum efficiency and decay time of TLA capped CdS QDs increased appreciably by lowering the pH value. The spectroscopic investigations confirmed that the pH-dependent luminescence (PL) behavior of as prepared TLA passivated CdS QDs is caused by structural changes of the QDs surface. Relatively at very low pH value QDs solution turns to turbid which designates the development of aggregates or clustres of CdS QDs. This is established by optical spectroscopy, AFM and TEM measurements.

Keywords: CdS, Photoluminescence, Quantum Dots, Inorganic Acid, Spectroscopy, Surface Engineering