Radiative recombination of triexcitons in CdSe colloidal quantum dots

Recent experimental observations of multiexciton recombination in colloidal CdSe quantum dots have revealed a high-energy emission band that has been attributed to the radiative recombination of a p-like electron with a p-like hole in a triexciton complex (three holes + three electrons). The reason for the occupation of p-like hole states in the triexciton, however, has remained elusive. Using atomistic pseudopotential calculations, we show here that p-like hole states are populated even at low temperature because of the relatively small Coulomb repulsion between s-like and p-like hole states, which leads to a non-Aufbau occupation sequence of the hole levels. We also show that the observed temperature dependence of the p-p emission band originates from the dark-bright splitting of the triexciton ground state. Our results provide a consistent explanation of the physical origin of the triexciton emission lines in CdSe quantum dots.