Nanoshell quantum dots (QDs) represent a novel class of colloidal semiconductor nanocrystals (NCs), which supports tunable optoelectronic properties over the extended range of particle sizes. Traditionally, the ability to control the bandgap of colloidal semiconductor NCs is limited to small-size nanostructures, where photoinduced charges are confined by Coulomb interactions. A notorious drawback of such a restricted size range concerns the fact that assemblies of smaller nanoparticles tend to exhibit a greater density of interfacial and surface defects. This presents a potential problem for device applications of semiconductor NCs where the charge transport across nanoparticle films is important, as in the case of solar cells, field-effect transistors, and photoelectrochemical devices. The morphology of nanoshell QDs addresses this issue by enabling the quantum-confinement in the shell layer, where two-dimensional excitons can exist, regardless of the total particle size. Such a geometry exhibits one of the lowest surface-to-volume ratios among existing QD architectures and, therefore, could potentially lead to improved charge-transport and multi-exciton characteristics. The expected benefits of the nanoshell architecture were recently demonstrated by a number of reports on the CdS_bulk/CdSe nanoshell model system, showing an improved photoconductivity of solids and increased lifetime of multi-exciton populations. Along these lines, this perspective will summarize the recent work on CdS_bulk/CdSe nanoshell colloids and discuss the possibility of employing other nanoshell semiconductor combinations in light-harvesting and lasing applications.

中文翻译：

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纳米壳量子点：超越激子玻尔半径的量子限制

纳米壳量子点（QDs）代表了一类新型的胶体半导体纳米晶体（NCs），它在扩展的粒径范围内支持可调的光电特性。传统上，控制胶体半导体NCs的带隙的能力仅限于小尺寸的纳米结构，在这种结构中，光感应电荷受库仑相互作用的限制。如此有限的尺寸范围的一个臭名昭著的缺点涉及较小纳米颗粒的组件倾向于表现出更高密度的界面缺陷和表面缺陷的事实。这对于半导体NC的设备应用提出了潜在的问题，其中跨纳米颗粒薄膜的电荷传输很重要，例如在太阳能电池，场效应晶体管和光电化学设备的情况下。纳米壳量子点的形态通过在壳层中实现量子约束来解决此问题，壳层中可以存在二维激子，而与总粒径无关。这种几何形状在现有QD架构中展现出最低的表面体积比之一，因此有可能潜在地改善电荷传输和多激子特性。纳米壳结构的预期好处最近在有关CdS的许多报告中得到了证明。_体/ CdSe纳米壳模型系统，显示了改进的固体光电导性和增加了多激子族的寿命。沿着这些思路，该观点将总结有关CdS_块体/ CdSe纳米壳胶体的最新工作，并讨论在光收集和激光应用中采用其他纳米壳半导体组合的可能性。