Center for Advanced Solar Photophysics, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
Nano Lett. 2011 Feb 9;11(2):687-93. doi: 10.1021/nl103801e. Epub 2011 Jan 5.
Spatial confinement of electronic excitations in semiconductor nanocrystals (NCs) results in a significant enhancement of nonradiative Auger recombination (AR), such that AR processes can easily dominate the decay of multiexcitons. AR is especially detrimental to lasing applications of NCs, as optical gain in these structures explicitly relies on emission from multiexciton states. In standard NCs, AR rates scale linearly with inverse NC volume. Here, we investigate multiexciton dynamics in hetero-NCs composed of CdSe cores and CdS shells of tunable thickness. We observe a dramatic decrease in the AR rates at the initial stage of shell growth, which cannot be explained by traditional volume scaling alone. Rather, fluorescence-line-narrowing studies indicate that the suppression of AR correlates with the formation of an alloy layer at the core-shell interface suggesting that this effect derives primarily from the "smoothing" of the confinement potential associated with interfacial alloying. These data highlight the importance of NC interfacial structure in the AR process and provide general guidelines for the development of new nanostructures with suppressed AR for future lasing applications.
半导体纳米晶体（NCs）中电子激发的空间限制导致非辐射俄歇复合（AR）显著增强，使得 AR 过程很容易主导多激子的衰减。AR 对 NCs 的激光应用尤其不利，因为这些结构中的光学增益明确依赖于多激子态的发射。在标准 NCs 中，AR 速率与 NC 体积的倒数呈线性关系。在这里，我们研究了由 CdSe 核和 CdS 壳组成的异质 NCs 中的多激子动力学，壳层厚度可调。我们观察到在壳层生长的初始阶段，AR 速率急剧下降，这不能仅用传统的体积缩放来解释。相反，荧光线宽研究表明，AR 的抑制与核壳界面处形成的合金层相关，这表明这种效应主要源于与界面合金化相关的限制势的“平滑”。这些数据突出了 NC 界面结构在 AR 过程中的重要性，并为开发具有抑制 AR 的新型纳米结构提供了指导，以用于未来的激光应用。
