Full alignment of dispersed colloidal nanorods by alternating electric fields

Abstract

The parallel alignment of an ensemble of colloidal nanorods may unleash their application as the optically anisotropic constituent in polarized fluorescent sheets or polarization-selective detectors. Here, we demonstrate that full alignment of colloidal CdSe/CdS nanorods in suspension can be achieved by applying AC electric fields. Alignment is monitored by the concurrent change of the optical transmission of the dispersion. By comparing the transmission measurements to a theoretical model encompassing both the permanent and induced dipole moments of the nanorods, we can attribute the alignment to the interaction between the electric field and the nanorod's permanent dipole moment. The permanent dipole moment, relaxation time, absorption anisotropy and critical frequency of the CdSe/CdS nanorods are determined. In addition, we show that the regime of full alignment enables the direct determination of the anisotropic absorption of CdSe/CdS nanorods. We find that the anisotropy in absorption for the CdSe dot is similar to that of the CdS rod, which we attribute to the similarity in dielectric constant and electric field in both materials.