Liu Ruibin, Shi Lijie, Zou Bingsuo
Beijing Key Lab of Nanophotonics and Ultrafine Optoeletronic Systems, Beijing Institute of Technology , Beijing 100081, China.
ACS Appl Mater Interfaces. 2014 Jul 9;6(13):10353-66. doi: 10.1021/am501835j. Epub 2014 Jun 25.
ZnO:Mn nanostructures are important diluted magnetic materials, but their electronic structure and magnetic origin are still not well understood. Here we studied the time-delayed and power-dependent photoluminescence spectra of Mn(II) doped ZnO nanowires with very low Mn concentration. From the time-delayed emission spectra, we obtained their electronic levels of single Mn ion replacement of Zn ions in ZnO nanowire. The high d-level emissions show up unusually because of the stronger p-d hybridization than that in ZnS, as well as the spin-spin coupling. After increasing Mn doping concentration, the ferromagentic cluster of the Mn-O-Mn with varied configurations can form and give individual emission peaks, which are in good agreement with the ab initio calculations. The presence of clustered Mn ions originates from their ferromagnetic coupling. The lifetimes of these d levels show strong excitation power-dependent behavior, indication of strong spin-dependent coherent emission. One-dimensional structure is critical for this coherent emission behavior. These results indicate that the d state is not within Mn ion only, but a localized exciton magnetic polaron, Mn-O-Mn coupling should be one source of ferromagnetism in ZnO:Mn lattice, the latter also can combine with free exciton for EMP and produce coherent EMP condensation and emission from a nanowire. This kind of nanowires can be expected to work for both spintronic and spin-photonic devices if we tune the transition metal ion doping concentration in it.
锰纳米结构是重要的稀磁材料，但其电子结构和磁性起源仍未得到很好的理解。在此，我们研究了极低锰浓度的锰（II）掺杂氧化锌纳米线的时间分辨和功率相关光致发光光谱。从时间分辨发射光谱中，我们获得了氧化锌纳米线中单个锰离子取代锌离子后的电子能级。由于比硫化锌中更强的p-d杂化以及自旋-自旋耦合，高d能级发射异常出现。增加锰掺杂浓度后，具有不同构型的锰-氧-锰铁磁团簇能够形成并给出各自的发射峰，这与从头算计算结果吻合良好。团簇状锰离子的存在源于它们的铁磁耦合。这些d能级的寿命表现出强烈的激发功率依赖行为，表明存在强自旋依赖的相干发射。一维结构对于这种相干发射行为至关重要。这些结果表明，d态并非仅存在于锰离子中，而是一个局域化的激子磁极化子，锰-氧-锰耦合应是氧化锌：锰晶格中铁磁性的一个来源，后者还可与自由激子结合产生电磁极化激元和纳米线的相干电磁极化激元凝聚与发射。如果我们调节其中过渡金属离子的掺杂浓度，这种纳米线有望应用于自旋电子学和自旋光子学器件。
