Excitons, Biexcitons, and Trions in CdSe Nanorods

We calculate the recombination energies and probabilities of neutral excitons (X), singly charged excitons (X-+/-), and biexcitons (XX) in CdSe quantum dots of variable length. For spherical dots the relative position of the emission lines is determined by the confinement. As the dot is elongated, however, Coulomb correlation overcomes single-particle effects and the emission line of X becomes more energetic than that of any other excitonic complex. Likewise, the recombination probability (tau(-1)) of spherical dots is characteristic of the strong confinement regime: tau(-1)(XX) similar to 2 tau(-1)(X-+/-) similar to 4 tau(-1)(X). However, these ratios are reduced with increasing length, as correlations enhance the emission of each excitonic complex at a different rate. Our results are compared with available experimental data.