Aggregates of Mn2+ Ions in Mesoporous Self-Assembled Cubic ZnS:Mn Quantum Dots: Composition, Localization, Structure, and Magnetic Properties

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• 作者：Sergiu V. Nistor ; Mariana Stefan ; Leona C. Nistor ; Victor Kuncser ; Daniela Ghica ; Ioana D. Vlaicu
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：July 7, 2016
• 年：2016
• 卷：120
• 期：26
• 页码：14454-14466
• 全文大小：671K
• 年卷期：0
• ISSN：1932-7455

文摘

The source of collective magnetism in II–VI semiconductor quantum dots (QDs) doped with Mn²⁺ ions at high nominal impurity levels is still under debate. In the particular case of mesoporous, self-assembled cubic ZnS:Mn QDs, quantitative electron paramagnetic resonance (EPR) studies have shown that the Mn²⁺ ions incorporated in the core and on the surface of the QDs cannot be responsible for the observed collective magnetism because they remain in a diluted paramagnetic state up to the 50 000 ppm nominal concentration. Here we investigate the composition, localization, structure, and magnetic properties of the aggregates of Mn²⁺ ions incorporated in the mesoporous cZnS:Mn as a possible source of the observed collective magnetism. Samples of mesoporous cubic ZnS:Mn prepared by coprecipitation at several nominal impurity levels from 200 to 50 000 ppm are investigated by EPR, magnetometry, and analytical high resolution (scanning) transmission electron microscopy. The low temperature magnetic properties of the Mn²⁺ aggregates change from paramagnetic-like, for samples with nominal impurity levels up to 2000 ppm, to ones specific to larger clusters with distributed antiferromagnetic coupling at higher concentrations, behaving superparamagnetically above a certain temperature. There is also strong evidence that the Mn²⁺ aggregates responsible for the observed low temperature collective magnetism are incorporated as an amorphous phase of mainly Mn–Zn–O composition, localized in the interstices and pores of the mesoporous structure of the cubic ZnS:Mn QDs.