CdS Magic-Sized Nanocrystals Exhibiting Bright Band Gap Photoemission via Thermodynamically Driven Formation

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• 作者：Minjie Li ; Jianying Ouyang ; Christopher I. Ratcliffe ; Laetitia Pietri ; Xiaohua Wu ; Donald M. Leek ; Igor Moudrakovski ; Quan Lin ; Bai Yang ; Kui Yu
• 刊名：ACS Nano
• 出版年：2009
• 出版时间：December 22, 2009
• 年：2009
• 卷：3
• 期：12
• 页码：3832-3838
• 全文大小：396K
• 年卷期：0
• ISSN：1936-086X

文摘

CdS magic-sized nanocrystals (MSNs) exhibiting both band gap absorption and emission at 378 nm with a narrow bandwidth of ∼9 nm and quantum yield (QY) of ∼10% (total QY ∼28%, in hexane) were synthesized via a one-pot noninjection approach. This CdS MSN ensemble is termed as Family 378. It has been acknowledged that magic-sized quantum dots (MSQDs) are single-sized, and only homogeneous broadening contributes to their bandwidth. The synthetic approach developed is ready and highly reproducible. The formation of the CdS MSQDs was carried out at elevated temperatures (such as 90−140 °C) for a few hours in a reaction flask containing bis(trimethylsilyl)sulfide ((TMS)₂S) and Cd(OAc)(OA) in situ made from cadmium acetate dihydrate (Cd(OAc)₂·2H₂O) and oleic acid (OA) in 1-octadecene (ODE). Low OA/Cd and high Cd/S feed molar ratios favor this formation, whose mechanism is proposed to be thermodynamically driven. ¹³C solid-state cross-polarization magic-angle spinning (CP/MAS) nuclear magnetic resonance (NMR) demonstrates that the capping ligands are firmly attached to the nanocrystal surface via carboxylate groups. With the cross-polarization from ¹H of the alkyl chains to surface ¹¹³Cd, ¹¹³Cd NMR is able to distinguish the surface Cd (471 ppm) bonding to both −COO⁻ and S and the bulk Cd (792 ppm) bonding to S only. DOSY-NMR was used to determine the size of Family 378 (∼1.9 nm). The present study provides strategies for the rational design of various MSNs.