Tuning the Potentials of 鈥淓xtra鈥?Electrons in Colloidal n-Type ZnO Nanocrystals via Mg2+ Substitution

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• 作者：Alicia W. Cohn ; Kevin R. Kittilstved ; Daniel R. Gamelin
• 刊名：The Journal of the American Chemical Society
• 出版年：2012
• 出版时间：May 9, 2012
• 年：2012
• 卷：134
• 期：18
• 页码：7937-7943
• 全文大小：375K
• 年卷期：v.134,no.18(May 9, 2012)
• ISSN：1520-5126

文摘

Colloidal reduced ZnO nanocrystals are potent reductants for one-electron or multielectron redox chemistry, with reduction potentials tunable via the quantum confinement effect. Other methods for tuning the redox potentials of these unusual reagents are desired. Here, we describe synthesis and characterization of a series of colloidal Zn_1鈥?i>xMg_xO and Zn_0.98鈥?i>xMg_xMn_0.02O nanocrystals in which Mg²⁺ substitution is used to tune the nanocrystal reduction potential. The effect of Mg²⁺ doping on the band-edge potentials of ZnO was investigated using electronic absorption, photoluminescence, and magnetic circular dichroism spectroscopies. Mg²⁺ incorporation widens the ZnO gap by raising the conduction-band potential and lowering the valence-band potential at a ratio of 0.68:0.32. Mg²⁺ substitution is far more effective than Zn²⁺ removal in raising the conduction-band potential and allows better reductants to be prepared from Zn_1鈥?i>xMg_xO nanocrystals than can be achieved via quantum confinement of ZnO nanocrystals. The increased conduction-band potentials of Zn_1鈥?i>xMg_xO nanocrystals compared to ZnO nanocrystals are confirmed by demonstration of spontaneous electron transfer from n-type Zn_1鈥?i>xMg_xO nanocrystals to smaller (more strongly quantum confined) ZnO nanocrystals.