Role of Solvent鈥揙xygen Ion Pairs in Photooxidation of CdSe Nanocrystal Quantum Dots
详细信息 查看全文
- 作者：Virginia W. Manner ; Alexey Y. Koposov ; Paul Szymanski ; Victor I. Klimov ; Milan Sykora
- 刊名：ACS Nano
- 出版年：2012
- 出版时间：March 27, 2012
- 年：2012
- 卷：6
- 期：3
- 页码：2371-2377
- 全文大小：343K
- 年卷期：v.6,no.3(March 27, 2012)
- ISSN：1936-086X
文摘
Understanding the mechanisms for photodegradation of nanocrystal quantum dots is an important step toward their application in real-world technologies. A usual assumption is that photochemical modifications in nanocrystals, such as their photooxidation, are triggered by absorption of a photon in the dot itself. Here, we demonstrate that, contrary to this commonly accepted picture, nanocrystal oxidation can be initiated by photoexcitation of solvent鈥搊xygen ion pairs that relax to produce singlet oxygen, which then reacts with the nanocrystals. We make this conclusion on the basis of photolysis studies of solutions of CdSe nanocrystals. Our measurements indicate a sharp spectral onset for photooxidation, which depends on solvent identity and is 4.8 eV for hexane and 3.4 eV for toluene. Importantly, the photooxidation onset correlates with the position of a new optical absorption feature, which develops in a neat solvent upon its exposure to oxygen. This provides direct evidence that nanocrystal photooxidation is mediated by excitation of solvent鈥搊xygen pairs and suggests that the stability of the nanocrystals is defined by not only the properties of their surfaces (as has been commonly believed) but also the properties of their environment, that is, of the surrounding solvent or matrix.