National Laboratory of Solid State Microstructures and School of Physics, Nanjing University, Nanjing 210093, China.
Nat Commun. 2012;3:1170. doi: 10.1038/ncomms2183.
Carrier multiplication describes an interesting optical phenomenon in semiconductors whereby more than one electron-hole pair, or exciton, can be simultaneously generated upon absorption of a single high-energy photon. So far, it has been highly debated whether the carrier multiplication efficiency is enhanced in semiconductor nanocrystals as compared with their bulk counterpart. The controversy arises from the fact that the ultrafast optical methods currently used need to correctly account for the false contribution of charged excitons to the carrier multiplication signals. Here we show that this charged exciton issue can be resolved in an energy transfer system, where biexcitons generated in the donor nanocrystals are transferred to the acceptor dyes, leading to an enhanced fluorescence from the latter. With the biexciton Auger and energy transfer lifetime measurements, an average carrier multiplication efficiency of ~17.1% can be roughly estimated in CdSe nanocrystals when the excitation photon energy is ~2.46 times of their energy gap.
载流子倍增描述了半导体中的一种有趣的光学现象，即单吸收一个高能光子可以同时产生超过一对电子-空穴对或激子。到目前为止，人们高度争论的是与体相比，半导体纳米晶体中的载流子倍增效率是否得到增强。这种争议源于目前使用的超快光学方法需要正确考虑带电荷激子对载流子倍增信号的虚假贡献。在这里，我们表明，在能量转移系统中可以解决这个带电荷激子的问题，其中施主纳米晶体中产生的双激子转移到受体染料上，从而使后者的荧光增强。通过双激子俄歇和能量转移寿命测量，当激发光子能量约为其能隙的 2.46 倍时，可以大致估计 CdSe 纳米晶体中的平均载流子倍增效率约为 17.1%。
