Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Phys Rev Lett. 2010 Apr 16;104(15):157403. doi: 10.1103/PhysRevLett.104.157403.
Semiconductor nanocrystals emit light intermittently; i.e., they "blink," under steady illumination. The dark periods have been widely assumed to be due to photoluminescence (PL) quenching by an Auger-like process involving a single additional charge present in the nanocrystal. Our results challenge this long-standing assumption. Close examination of exciton PL intensity time traces of single CdSe(CdZnS) core(shell) nanocrystals reveals that the dark state PL quantum yield can be 10 times less than the biexciton PL quantum yield. In addition, we observe spectrally resolved multiexciton emission and find that it also blinks with an on/off ratio greater than 10:1. These results directly contradict the predictions of the charging model.
半导体纳米晶体在稳定光照下会间歇发光；也就是说，它们会“闪烁”。暗态期一直被广泛认为是由于俄歇过程中的光致发光（PL）猝灭所致，该过程涉及纳米晶体中存在的单个额外电荷。我们的结果对这一长期存在的假设提出了挑战。对单个 CdSe(CdZnS)核/壳纳米晶体的激子 PL 强度时间轨迹的仔细检查表明，暗态 PL 量子产率可以比双激子 PL 量子产率低 10 倍。此外，我们观察到了光谱分辨的多激子发射，并发现它也以大于 10:1 的开/关比闪烁。这些结果直接与充电模型的预测相矛盾。
