Room temperature measurements of the 3D orientation of single CdSe quantum dots using polarization microscopy.

Simple far-field emission polarization microscopy reveals that the emission transition dipole of CdSe colloidal quantum dots (QDs) is twofold degenerate at room temperature. We measure, model, and compare polarization anisotropy statistics of CdSe QDs and DiI (a one-dimensional emitter). We find excellent agreement between experiment and theory if the transition dipole of CdSe QDs is assumed to be twofold degenerate. This implies that the three-dimensional orientation of the unique crystal axis in QDs can be determined at room temperature with polarization microscopy. We describe an optical setup to measure four polarization angles of multiple single QDs simultaneously and in real time (approximately equal to 16 Hz). We use this setup in a proof-of-concept experiment to demonstrate that the rotational motion of QDs can be monitored in various host matrices.