Band-Edge Exciton in CdSe and Other II-VI and III-V Compound Semiconductor Nanocrystals - Revisited.

In this Mini Review, we summarize major corrections to the dark-bright exciton theory [ Efros et al. Phys. Rev B 1996 , 54 , 4843 - 4856 ], which should be used for quantitative description of the band edge exciton in II-VI and III-V compound quantum-dot nanocrystals (NCs). The theory previously did not take into account the long-range exchange interaction, resulting in the under-estimation of the splitting between the upper bright and lower dark or quasi-dark exciton, as reported by several experimental groups. Another type of correction originates from the closeness in energy of the ground, 1S3/2, and the first excited, 1P3/2, hole levels in a spherical NC, resulting in significant energetic overlap of the levels from the 1S3/21Se and 1P3/21Se exciton manifolds connected with the ground 1Se electron level. The thermal occupation of the optically forbidden 1P3/21Se exciton levels changes the radiative decay time of the NCs at both helium and room temperatures. We demonstrate the role of both effects in CdSe NCs and compare our predictions with available experimental data.