Hiroshige Nao, Ihara Toshiyuki, Saruyama Masaki, Teranishi Toshiharu, Kanemitsu Yoshihiko
Institute for Chemical Research, Kyoto University , Uji, Kyoto 611-0011, Japan.
J Phys Chem Lett. 2017 May 4;8(9):1961-1966. doi: 10.1021/acs.jpclett.7b00547. Epub 2017 Apr 18.
Giant-shell CdSe/CdS core/shell nanocrystals have attracted much attention due to their unique quasi-type-II band alignment, where a large valence band offset confines holes strongly to the core but electrons are delocalized due to a small conduction band offset. Here, we report the observation of the relative enhancement in the radiative recombination rate of a biexciton compared to that of an exciton in giant-shell CdSe/CdS nanocrystals. We found a clear correlation between the shell thickness of the CdSe/CdS nanocrystals and the ratio between the radiative recombination rates of the biexciton and exciton. Our finding can be explained by a picture in which the biexciton emission efficiency is enhanced through electron localization around the core due to the strong Coulomb potential of the two holes confined in the core.
巨型壳层CdSe/CdS核壳纳米晶体因其独特的准II型能带排列而备受关注，在这种排列中，较大的价带偏移将空穴强烈限制在核内，而由于较小的导带偏移，电子则是离域的。在此，我们报告了在巨型壳层CdSe/CdS纳米晶体中，双激子的辐射复合率相对于激子的辐射复合率有相对增强的观测结果。我们发现CdSe/CdS纳米晶体的壳层厚度与双激子和激子的辐射复合率之比之间存在明显的相关性。我们的发现可以用这样一幅图景来解释：由于限制在核内的两个空穴具有很强的库仑势，双激子发射效率通过电子在核周围的局域化而得到增强。
