Low-Temperature Growth of Inverted Hexagonal ZnS/CdS Quantum Dots: Functional and Luminescence Properties

A novel low-temperature wet chemical method is proposed for direct growth of type-I inverted hexagonal ZnS/CdS quantum dots (QD). 2-Mercaptoethanol (2-ME) was used as a capping agent for confinement by passivation, and also helped to prevent agglomeration of the QD. The band gap calculated from optical absorption spectra was 2.63 eV for the smallest core/shell QD. Absorption edge onset and results from transmission electron microscopy revealed formation of inverted core/shell QD. X-ray diffraction studies revealed the ZnS/CdS had a stable hexagonal crystal structure at low temperature. The average diameter of the core/shell QD was 4.2 nm. Tunable luminescence with substantial tunability was revealed by study of the photoluminescence of the inverted ZnS/CdS quantum dots. Surface passivation of ZnS/CdS QD by 2-ME was confirmed by Fourier-transform infrared spectroscopy.