ACS Nano. 2015 Apr 28;9(4):3942-50. doi: 10.1021/nn507310f. Epub 2015 Apr 9.
Semiconductors are indispensable as the active light-emitting element in many optoelectronic devices. However, even the purest bulk semiconductors suffer from considerable nonradiative recombination leading to low photoluminescence efficiencies. Zero-dimensional quantum dots show a much better carrier-to-photon conversion caused by confinement of the excitons but suffer from nonradiative recombination when assembled into a solid, due to exciton energy transfer. Here, we report on the shape-dependent optical properties of self-assembled supraparticles composed of CdSe/multishell nanocrystals. All supraparticles show stable and bright photoluminescence in ambient up to high excitation intensities. When the supraparticles are deposited on a silicon surface their spherical shape is deformed due to drying. In addition to single-exciton emission, we observe bright emission from multiexciton states at high excitation powers. In contrast, supraparticles that retain their perfectly spherical shape show a spectrum with sharp Mie whispering gallery modes, while multiexciton emission is absent.
半导体是许多光电设备中活跃的发光元件不可或缺的。然而，即使是最纯净的体半导体也会遭受相当大的非辐射复合，导致光致发光效率低。零维量子点由于激子的限制表现出更好的载流子-光子转换，但在组装成固体时由于激子能量转移而遭受非辐射复合。在这里，我们报告了由 CdSe/多壳层纳米晶体自组装而成的超粒子的形状依赖性光学性质。所有超粒子在环境中直至高激发强度下都表现出稳定而明亮的光致发光。当超粒子沉积在硅表面上时，由于干燥它们的球形形状会变形。除了单激子发射外，我们还在高激发功率下观察到来自多激子态的明亮发射。相比之下，保留完美球形形状的超粒子显示出具有尖锐的米氏 whispering gallery 模式的光谱，而不存在多激子发射。
