Exciton-bath coupling and inhomogeneous broadening in the optical spectroscopy of semiconductor quantum dots

The homogeneous line shape and inhomogeneous broadening of colloidal quantum dots are measured at ambient temperatures and in solution. Three-pulse echo peak shift (3PEPS) measurements of nanocrystalline CdSe semiconductor quantum dots in toluene solvent at 298 K are reported. Modeling of the 3PEPS data using a detailed model designed to account for the optical properties of semiconductor quantum dots, suggests that Debye-type relaxations attributed to reorientation of the trioctylphosphine and trioctyl phosphine oxide capping ligands are significant. It is shown that 3PEPS spectroscopy can quantify precisely the inhomogeneous broadening of the optical spectrum, brought about mainly by the distribution of nanocrystal sizes. (C) 2003 American Institute of Physics.