Near-Infrared Photoluminescence Enhancement in Ge/CdS and Ge/ZnS Core/Shell Nanocrystals: Utilizing IV/II鈥揤I Semiconductor Epitaxy
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- 作者：Yijun Guo ; Clare E. Rowland ; Richard D. Schaller ; Javier Vela
- 刊名：ACS Nano
- 出版年：2014
- 出版时间：August 26, 2014
- 年：2014
- 卷：8
- 期：8
- 页码：8334-8343
- 全文大小：614K
- ISSN：1936-086X
文摘
Ge nanocrystals have a large Bohr radius and a small, size-tunable band gap that may engender direct character via strain or doping. Colloidal Ge nanocrystals are particularly interesting in the development of near-infrared materials for applications in bioimaging, telecommunications and energy conversion. Epitaxial growth of a passivating shell is a common strategy employed in the synthesis of highly luminescent II鈥揤I, III鈥揤 and IV鈥揤I semiconductor quantum dots. Here, we use relatively unexplored IV/II鈥揤I epitaxy as a way to enhance the photoluminescence and improve the optical stability of colloidal Ge nanocrystals. Selected on the basis of their relatively small lattice mismatch compared with crystalline Ge, we explore the growth of epitaxial CdS and ZnS shells using the successive ion layer adsorption and reaction method. Powder X-ray diffraction and electron microscopy techniques, including energy dispersive X-ray spectroscopy and selected area electron diffraction, clearly show the controllable growth of as many as 20 epitaxial monolayers of CdS atop Ge cores. In contrast, Ge etching and/or replacement by ZnS result in relatively small Ge/ZnS nanocrystals. The presence of an epitaxial II鈥揤I shell greatly enhances the near-infrared photoluminescence and improves the photoluminescence stability of Ge. Ge/II鈥揤I nanocrystals are reproducibly 1鈥? orders of magnitude brighter than the brightest Ge cores. Ge/4.9CdS core/shells show the highest photoluminescence quantum yield and longest radiative recombination lifetime. Thiol ligand exchange easily results in near-infrared active, water-soluble Ge/II鈥揤I nanocrystals. We expect this synthetic IV/II鈥揤I epitaxial approach will lead to further studies into the optoelectronic behavior and practical applications of Si and Ge-based nanomaterials.