The role of ion exchange in the passivation of In(Zn)P nanocrystals with ZnS

• Published in: Scientific reports Vol. 6; no. 1; p. 22818
• Main Authors: Cho, Deok-Yong, Xi, Lifei, Boothroyd, Chris, Kardynal, Beata, Lam, Yeng Ming
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 14.03.2016; Nature Publishing Group
• Subjects: 639/301/357/354; 639/925/930/12; Absorption spectroscopy; Color; Crystals; Humanities and Social Sciences; Ion exchange; Ions; Luminescence; multidisciplinary; Nanocrystals; Photons; Science; Science (multidisciplinary); Shells; Spectroscopy; Spectrum analysis; Ultrastructure; X-ray absorption spectroscopy; X-rays; Zinc
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/srep22818

We have investigated the chemical state of In(Zn)P/ZnS core/shell nanocrystals (NCs) for color conversion applications using hard X-ray absorption spectroscopy (XAS) and photoluminescence excitation (PLE). Analyses of the edge energies as well as the X-ray absorption fine structure (XAFS) reveal that the Zn 2+ ions from ZnS remain in the shell while the S 2− ions penetrate into the core at an early stage of the ZnS deposition. It is further demonstrated that for short growth times, the ZnS shell coverage on the core was incomplete, whereas the coverage improved gradually as the shell deposition time increased. Together with evidence from PLE spectra, where there is a strong indication of the presence of P vacancies, this suggests that the core-shell interface in the In(Zn)P/ZnS NCs are subject to substantial atomic exchanges and detailed models for the shell structure beyond simple layer coverage are needed. This substantial atomic exchange is very likely to be the reason for the improved photoluminescence behavior of the core-shell particles compare to In(Zn)P-only NCs as S can passivate the NCs surfaces.