Size Dependence of the Spontaneous Emission Rate and Absorption Cross Section of CdSe and CdTe Quantum Dots
Size Dependence of the Spontaneous Emission Rate and Absorption Cross Section of CdSe and CdTe Quantum Dots
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DOI：
10.1021/jp811329r
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发表时间：
2009-04-23
影响因子：
3.7
通讯作者：
Koole, Rolf
中科院分区：
文献类型：
--
作者：
Donega, Celso de Mello;Koole, Rolf
在本文中，带隙的尺寸依赖性，自发辐射率，和吸收截面的量子点在很宽的尺寸范围内进行了系统的研究，使用胶体CdSe和CdTe量子点作为模型系统（直径范围从1.2到8 nm和从2到9.5 nm，分别）。带隙的尺寸依赖性由理论模型很好地描述，并且由量子限制贡献（1/d（2）标度）主导。自发辐射率随发射频率线性增加的CdSe和CdTe量子点，在良好的协议与理论预测。通过将发射速率的频率依赖性外推到体带隙值，可以首次估计体CdSe和CdTe中的激子辐射寿命（即，分别为18和20 ns）。经验趋势和理论预测之间的比较提供了新的基本见解量子点的1 S（（e））1 S（3/2（h））振子强度的大小依赖性，无论是发射和吸收。结果突出了量子限制和库仑相互作用贡献之间的平衡的重要性，量子点中的激子性质的尺寸依赖性，并提供了一个解释的经验尺寸依赖的趋势和理论预测之间观察到的长期存在的差异。辐射衰减率和吸收截面的尺寸依赖性之间的差异被证明是由于发射和吸收跃迁之间的根本差异（即，自发与受激）。从实际的角度来看，结果也是相关的，因为它们表明，在远高于带隙的能量摩尔消光系数更适合于分析目的。此外，更广泛和准确的尺寸曲线提供了CdSe和CdTe量子点。
In this paper, the size dependence of the band gap, of the spontaneous emission rate, and of the absorption cross section of quantum dots is systematically investigated over a wide size range, using colloidal CdSe and CdTe QDs as model systems (diameters ranging from 1.2 to 8 nm and from 2 to 9.5 nm, respectively). The size dependence of the band gap is well-described by theoretical models, and is dominated by the quantum confinement contribution (1/d(2) scaling). The spontaneous emission rate increases linearly with the emission frequency for both CdSe and CdTe QDs, in good agreement with theoretical predictions. By extrapolating the frequency dependence of the emission rates to the bulk band gap values, the exciton radiative lifetime in bulk CdSe and CdTe could be estimated for the first time (viz., 18 and 20 ns, respectively). Comparison between the empirical trends and theoretical predictions provides new fundamental insights into the size dependence of the 1S((e))1S(3/2(h)) oscillator strengths of QDs, both for emission and absorption. The results highlight the importance of the balance between quantum confinement and coulomb interaction contributions to the size dependence of the exciton properties in QDs and offer an explanation to the long-standing discrepancies observed between the empirical size-dependent trends and the theoretical predictions. The difference between the size dependence of the radiative decay rates and of the absorption cross sections is shown to be due to the fundamental differences between the emission and absorption transitions (viz., spontaneous versus stimulated). The results are also relevant from a practical viewpoint, since they show that the molar extinction coefficients at energies far above the band gap are better suited for analytical purposes. Moreover, more extended and accurate sizing curves are provided for CdSe and CdTe QDs.