HgS and HgS/CdS Colloidal Quantum Dots with Infrared Intraband Transitions and Emergence of a Surface Plasmon

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• 作者：Guohua Shen ; Philippe Guyot-Sionnest
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：June 2, 2016
• 年：2016
• 卷：120
• 期：21
• 页码：11744-11753
• 全文大小：644K
• 年卷期：0
• ISSN：1932-7455

文摘

HgS colloidal quantum dots (CQDs) are synthesized at room temperature using a dual-phase method. The HgS CQDs ranging from 3 to 15 nm exhibit air-stable n-doping and infrared intraband absorptions. For HgS CQDs of small sizes, the doping density is close to 2 electrons per dot, while for larger ones, their intraband absorption peaks shift to as far as 10 μm and exhibit Lorentzian line shapes. Under reducing potentials, these long-wavelength absorption peaks increase in strength and blue shift. This behavior can be explained through a classical model of the local field, showing how the degenerate single-electron transitions shift to a frequency that is the quadratic mean of the individual transition and a surface plasmon coming from a number of oscillators. This indicates that the intraband absorption of large, n-doped HgS CQDs is therefore becoming a surface plasmon. The same synthetic method works for HgS/CdS core/shells. Encapsulating HgS in a CdS shell removes the natural n-doping of the HgS cores, resulting in an interband photoluminescence at 1.5 μm with ∼5% quantum yield. The n-doping partially recovers upon film formation, and increases in strength after ligand exchange and annealing. The core/shell greatly improves the thermal stability of the HgS cores, allowing an annealing temperature as high as 200 °C.