Tuning Equilibrium Compositions in Colloidal Cd1–xMnxSe Nanocrystals Using Diffusion Doping and Cation Exchange

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• 作者：Charles J. Barrows ; Pradip Chakraborty ; Lindsey M. Kornowske ; Daniel R. Gamelin
• 刊名：ACS Nano
• 出版年：2016
• 出版时间：January 26, 2016
• 年：2016
• 卷：10
• 期：1
• 页码：910-918
• 全文大小：458K
• ISSN：1936-086X

文摘

The physical properties of semiconductor nanocrystals can be tuned dramatically via composition control. Here, we report a detailed investigation of the synthesis of high-quality colloidal Cd_1–xMn_xSe nanocrystals by diffusion doping of preformed CdSe nanocrystals. Until recently, Cd_1–xMn_xSe nanocrystals proved elusive because of kinetic incompatibilities between Mn²⁺ and Cd²⁺ chemistries. Diffusion doping allows Cd_1–xMn_xSe nanocrystals to be prepared under thermodynamic rather than kinetic control, allowing access to broader composition ranges. We now investigate this chemistry as a model system for understanding the characteristics of nanocrystal diffusion doping more deeply. From the present work, a Se^2–-limited reaction regime is identified, in which Mn²⁺ diffusion into CdSe nanocrystals is gated by added Se^2–, and equilibrium compositions are proportional to the amount of added Se^2–. At large added Se^2– concentrations, a solubility-limited regime is also identified, in which x = x_max = ～0.31, independent of the amount of added Se^2–. We further demonstrate that Mn²⁺ in-diffusion can be reversed by cation exchange with Cd²⁺ under exactly the same reaction conditions, purifying Cd_1–xMn_xSe nanocrystals back to CdSe nanocrystals with fine tunability. These chemistries offer exceptional composition control in Cd_1–xMn_xSe NCs, providing opportunities for fundamental studies of impurity diffusion in nanocrystals and for development of compositionally tuned nanocrystals with diverse applications ranging from solar energy conversion to spin-based photonics.