Abstract

A commonly accepted picture of the transition dipole structure of colloidal semiconductor quantum dots is the so-called 2D degenerate dipole. Optical transitions in CdSe-ZnS quantum dot occur primarily for the low energy state for which the total spin angular momentum projection axis is J=±1. These transitions involve X+iY and X-iY combinations of the (hole) Bloch functions along the QD “X” and “Y” axis; in a spherical approximation, there are equal dipole strengths along two orthogonal axes in the QD frame resulting in a 2D degenerate dipole. This 2D dipole model has been used by Bawendi et al.[1] in their studies of quantum dot emission properties and Enderlein et al.[2] in their studies of quantum dot radiation patterns, and also provides a useful prototype of the complicated dipole structure for chiral nanosystems. Despite reliance on this model, a definitive study demonstrating the dipole structure of CdSe-ZnS quantum dots has not yet been performed. However, as demonstrated by Efros[3], transitions between the |1Se > z electron state and |1Se_3/2 > hole state contain projections along the quantum dot Z-axis. During excitation, this transition is forbidden; however, non-radiative energy transfer can make this transition allowed during emission. This 3^rd dipole component can, in principle, produce a noticeable effect in the observed linear polarization anisotropy of the light emitted from the quantum dot and observed interference patterns.

© 2010 Optical Society of America