Fine Structure of PbSe Colloidal Nanostructures

Although much work has been done on PbSe nanocrystals in order to understand excited states, little is known of the ground state fine structure. Bulk PbSe is an unusual semiconductor material with a direct band gap at the L point. The band structure at this symmetry point is four-fold degenerate for both electrons and light holes, and conduction and valence bands possess similar effective masses and g-factors. In this work, we synthesized high quality PbSe nanocrystals and characterized them using transmission electron microscopy and optical methods. We probed the g-factors and fine structure of excitons in undoped PbSe quantum dots using optically detected magnetic resonance (ODMR) at 24 GHz and polarized photoluminescence in a magnetic field. The results show that the dark states in this system are active even in the absence of external magnetic fields mainly due to thermal population.