Norberg Nick S, Parks Gregory L, Salley G Mackay, Gamelin Daniel R
Department of Chemistry, Box 351700, University of Washington, Seattle, 98195-1700, USA.
J Am Chem Soc. 2006 Oct 11;128(40):13195-203. doi: 10.1021/ja063425f.
Colloidal Co(2+):ZnSe diluted magnetic semiconductor quantum dots (DMS-QDs) were prepared by the hot injection method and studied spectroscopically. Ligand-field electronic absorption and magnetic circular dichroism (MCD) spectra confirm homogeneous substitutional speciation of Co(2+) in the ZnSe QDs. Absorption spectra collected at various times throughout the syntheses reveal that dopants are absent from the central cores of the QDs but are incorporated at a constant concentration during nanocrystal growth. The undoped cores are associated with dopant exclusion from the ZnSe critical nuclei. Analysis of low-temperature electronic absorption and MCD spectra revealed excitonic Zeeman splitting energies (DeltaE(Zeeman)) of these Co(2+):ZnSe QDs that were substantially smaller than anticipated from bulk Co(2+):ZnSe data. This reduction in DeltaE(Zeeman) is explained quantitatively by the absence of dopants from the QD cores, where dopant-exciton overlap would be greatest. Since dopant exclusion from nucleation appears to be a general phenomenon for DMS-QDs grown by direct chemical methods, we propose that DeltaE(Zeeman) will always be smaller in colloidal DMS-QDs grown by such methods than in the corresponding bulk materials.
通过热注入法制备了胶体Co(2+):ZnSe稀释磁性半导体量子点（DMS-QDs），并进行了光谱研究。配体场电子吸收光谱和磁圆二色性（MCD）光谱证实了Co(2+)在ZnSe量子点中的均匀取代形态。在整个合成过程中的不同时间收集的吸收光谱表明，量子点的中心核中没有掺杂剂，但在纳米晶体生长过程中以恒定浓度掺入。未掺杂的核与ZnSe临界核中掺杂剂的排除有关。对低温电子吸收光谱和MCD光谱的分析表明，这些Co(2+):ZnSe量子点的激子塞曼分裂能（DeltaE(Zeeman)）远小于从块状Co(2+):ZnSe数据预期的值。DeltaE(Zeeman)的这种降低可以通过量子点核中没有掺杂剂来定量解释，在量子点核中掺杂剂与激子的重叠最大。由于通过直接化学方法生长的DMS-QDs中，成核过程中掺杂剂的排除似乎是一种普遍现象，我们提出，通过这种方法生长的胶体DMS-QDs中的DeltaE(Zeeman)总是会比相应的块状材料中的小。
