Band-edge excitons in PbSe nanocrystals and nanorods

Abstract

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 $88\text{ }\ensuremath{\mu}\text{eV}$ for nanorods, and less than $20\text{ }\ensuremath{\mu}\text{eV}$ for nanocrystals. The intervalley splitting of the electron and hole levels in the nanocrystals is much larger than the electron-hole exchange interaction.