Band-edge excitons in PbSe nanocrystals and nanorods

We investigate the fine structure of band-edge excitons in PbSe nanocrystals and nanorods using circularly polarized magnetophotoluminescence and optically detected magnetic resonance and, based on the results, propose a singlet-triplet model of exciton photoluminescence from nondegenerate conduction and valence bands. From the data and model we extract g-factors for electrons and holes of +1.2 and +0.8, respectively. The splitting of the triplet ground state, which is responsible for the low-temperature photoluminescence, is 88 mu eV for nanorods, and less than 20 mu eV for nanocrystals. The intervalley splitting of the electron and hole levels in the nanocrystals is much larger than the electron-hole exchange interaction.