Optical anisotropy in individual CdS quantum dot ensembles

The polarized microphotoluminescence (PL) spectroscopy of individual spherical and rod-shaped CdS quantum dot (QD) ensembles has been investigated. In a spherical QD ensemble, optical anisotropy was observed despite the spherical shapes of both the ensemble and individual QD components. The directions of the maximum linearly polarized PL were different for different spherical QD ensembles, and independent on the polarization direction of the excitation. However, for a fixed polarization direction of PL, the PL yield significantly varied with the polarization direction of the excitation. In a rod-shaped QD ensemble, the direction of maximum polarized PL was observed to be perpendicular to the length direction of the rod, regardless of the polarization direction of the excitation. The observed PL anisotropies in individual spherical and rod-shaped QD ensembles are explained in terms of the crystallographic orientation of the individual QD components that make up the ensemble and obey the linear polarization selection rules. A statistic model is proposed to qualitatively describe the degree of polarization based on a three-dimensional crystallographic orientation of QDs with respect to the directions of excitation and observation.