Light Induced Electron Transfer Processes in Surface Engineeered Eco-friendly CuInS2 Quantum Dots

Abstract

Fundamental photophysical studies in eco-friendly as well as biocompatible quantum dots (QDs) are essential to realize the unique size dependent optoelectronic properties of QDs in practical applications. In this regard, the current thesis focuses on investigating the light harvesting properties in Copper Indium Sulphide (CuInS2) QDs. A precise surface engineering helped in imparting aqueous stability and tuning of surface charge of CuInS2/ZnS (CIS) QDs, with ~60% retention of its photoluminescence quantum yield. Further, the ability of CIS QDs to participate in light harvesting processes in aqueous medium is investigated. A light induced electron transfer in the Near Infrared (NIR) region is successfully demonstrated with CIS QDs as the donor and Indocyanine green (ICG) dye as the acceptor. The process of electron transfer was confirmed by carrying out quenching experiments under (i) Ar atmosphere, (ii) varying temperature and (iii) different solvent polarity. The efficiency of electron transfer was estimated to be as high as 85 % in aqueous medium, which is attributed to the strong electrostatic attraction between cationic CIS QD and anionic ICG dye. The use of CIS QDs as an efficient electron donor was extended towards methylene blue acceptor dye as well. Our studies help in expanding the scope of ecofriendly CuInS2 QDs beyond organic solvents, thereby enabling its future potential use in both optoelectronic and biomedical applications.