Fabrication of high quantum yield of CIS/ZnS quantum dots

Semiconductor quantum dots (QDs) are emerging luminescent nanomaterials. It can be used in solid-state lighting (SSL), display, solar cells and biomedical imaging due to the exhibit excellent wavelength tunability, large excitation range, consistent particle size and high quantum efficiency. In solid state lighting, white light-emitting diodes (LEDs) are often made by using QDs such as CdSe or ZnCdSe. However, cadmium-based QDs have limited future applications owing to the well-known toxicity. Recently, cadmium-free luminescent materials-CuInS₂/ZnS (CIS/ZnS) core/shell QDs are investigated. The CIS/ZnS QDs exhibit very broad emission spectrum, large Stoke's shift, and tunable emission wavelengths. Those properties make the CIS/ZnS QDs suitable for solid-state lighting application. In this study, CIS QDs with molar ratio of Cu:In is equal to 1:4, and the ZnS shell was produced by different shell sulfide precursors, such as dodecanethiol (DDT), octadecanethiol (ODT) and sulfur (S) powders. The optical properties, morphologies, and crystal structure are analysis by fluorescence spectrometer, UV-Vis spectrometer, transmission electron microscopy, and X-ray diffractometer, respectively. The results show that the emission wavelength and quantum yield (QY) of CIS/ZnSDDT, CIS/ZnSODT, and CIS/ZnSS are 549 nm, 76 %, 548 nm, 82 %, and 538 nm, 83 %, respectively. The structure of CIS/ZnS QD belongs to chalcopyrite phase and the average particle size is 3.2 nm. Moreover, the stability of CIS/ZnS QDs is excellent.