Structural and optical characterization of CuInS2 quantum dots synthesized by microwave-assisted continuous flow methods
Semiconductor quantum dots (QDs) have recently been incorporated into consumer displays and lighting technologies. Now that these materials are being produced on industrial scales, it is important to investigate scalable synthetic methods and less toxic materials and chemistries. To achieve these goals, we have synthesized cadmium-free, visible light-emitting QDs using a microwave-assisted continuous flow reactor. After synthesis, the CuInS2 QD cores underwent a near-complete Zn cation exchange reaction in a batch reactor, followed by the growth of a ZnS shell. Analysis of X-ray diffraction, transmission electron microscopy, and Raman spectroscopy data indicate that the crystal structure changes from CuInS2 (chalcopyrite) to ZnS (zincblende) during the cation exchange reaction. Compositional analysis indicated that the core/shell QDs were ~98 % ZnS, with Cu and In present at much lower concentrations. The photoluminescence (PL) peak position was blue shifted for longer cation exchange reactions, and it was found that the ZnS shell was necessary for improved PL stability. The synthesized QDs have a PL down conversion efficiency of ~65 % when using a blue LED source.
KeywordsQuantum dot Microwave-assisted continuous flow synthesis CuInS2 Cation exchange Semiconductor nanostructures
R.C.F. and G.S.H. gratefully acknowledge support from Oregon BEST. R.P.O. gratefully acknowledges support from the Center for Sustainable Materials Chemistry, which was supported by the US National Science Foundation under grant number CHE-1102637. We also gratefully acknowledge financial support for acquisition of the TEM through the US National Science Foundation Major Research Instrumentation (MRI) Program under Grant No. 1040588, the Murdock Charitable Trust, and the Oregon Nanoscience and Microtechnologies Institute.
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