Size and structure effect on optical transitions of iron oxide nanocrystals
Size and structure effect on optical transitions of iron oxide nanocrystals
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DOI：
10.1103/physrevb.71.125411
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发表时间：
2005-03-01
影响因子：
3.7
通讯作者：
Burda, C
中科院分区：
文献类型：
--
作者：
He, YP;Miao, YM;Burda, C
过渡金属氧化物的电子态的不均匀性产生了各种性质，这可以通过测量它们的纳米晶体来辨别。研究了化学合成的不同尺寸的纯Fe_3 O_4、γ-Fe_2 O_3和α-Fe_2 O_3纳米晶的结构和光谱。三种类型的电子跃迁：配位体到金属的电荷转移跃迁，强磁耦合的Fe 3，配位场跃迁，和对激发，发生明显的γ-Fe 2 O3和α-Fe 2 O3纳米晶体的光谱中，除了Fe 3 O 4。虽然纳米晶体是强电子关联系统，但在纳米晶体中观察到了量子尺寸效应（对于巡游载流子）和有限尺寸效应（对于局域磁矩）。局域化的电子离域转换发生在α-Fe 2 O3溶胶的飞秒瞬态吸收光谱的时间延迟，这表明，heterosesponse时间为不同的过渡同意与这些铁氧化物纳米晶体的稳态吸收带的尺寸依赖性的指示。这些结果有助于理解过渡金属氧化物中d-d跃迁、磁性配对和电荷转移之间的关系。
The heterogeneity of electronic states of transition metal oxides produces a variety of properties, which may be discerned by the measurements of their nanocrystals. The structure and optical spectra of chemically synthesized pure Fe3O4, gamma-Fe2O3, and alpha-Fe2O3 nanocrystals of different sizes have been investigated. Three types of electronic transitions: ligand to metal charge-transfer transitions, strong magnetic coupled Fe 3, ligand field transitions, and pair excitations, occur distinctly in the optical spectra of gamma-Fe2O3 and alpha-Fe2O3 nanocrystals except Fe3O4. The quantum size effect (for itinerant carriers) and finite size effect (for local magnetic moments) were observed in our nanocrystals, although their bulks are strong electron correlation systems. The localized to delocalized transformation of electrons occurs with time delay in the fermosecond transient absorption spectra of alpha-Fe2O3 nanocrystal sol, which indicates that heteroresponse times for different transitions agree well with the size-dependent indication of the steady-state absorption bands of these iron oxides nanocrystals. These results are helpful in understanding the relationship among d-d transition, magnetic pairing, and charge-transfer in transition metal oxides.