title: Carrier multiplication in semiconductor nanocrystals detected by energy transfer to organic dye molecules.
abstract: 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.
authors.affiliation: National Laboratory of Solid State Microstructures and School of Physics, Nanjing University, Nanjing 210093, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Xiao
authors.forename: Ying
authors.initials: Y
authors.lastname: Wang
authors.forename: Zheng
authors.initials: Z
authors.lastname: Hua
authors.forename: Xiaoyong
authors.initials: X
authors.lastname: Wang
authors.forename: Chunfeng
authors.initials: C
authors.lastname: Zhang
authors.forename: Min
authors.initials: M
authors.lastname: Xiao