Interpreting the Energy-Dependent Anisotropy of Colloidal Nanorods Using Ensemble and Single-Particle Spectroscopy

We report the use of polarized excitation spectroscopy in the study of the polarized optical properties of II-VI semiconducting nanorods. This technique provides a quantitative measure for analyzing the polarization-dependent electronic structure of ensembles of semiconducting nanoparticles in colloidal solutions. We develop a procedure to quantify the anisotropy of nanorod excitations and the influence of the dielectric environment which yields results in qualitative agreement with theoretical predictions of nanorod absorption properties. Excitation measurements of nanorod ensembles and single-particle excitation and emission polarization measurements are used to interpret ensemble measurements on the molecular frame. At the single-particle level, we find a large dispersion in the angles between excitation and emission polarization curves. This contrasts with the conventional picture of CdSe electronic transitions, in which the crystal axes dictate the symmetry of excitations. Such geometrically heterogeneous excitations suggest that perturbations of the physical structure adjust the polarization properties of individual nanorods from those of an ideal theoretical nanorod.