Measurement of Three-Dimensional Dipole Orientation of a Single Fluorescent Nanoemitter by Emission Polarization Analysis

Abstract

International audienceWe demonstrate theoretically and experimentally that the three-dimensional orientation of a single fluorescent nanoemitter can be determined by polarization analysis of the emitted light (while excitation polarization analysis provides only the in-plane orientation). The determination of the emitter orientation by polarimetry requires a theoretical description, including the objective numerical aperture, the 1D or 2D nature of the emitting dipole, and the environment close to the dipole. We develop a model covering most experimentally relevant microscopy configurations and provide analytical relations that are useful for orientation measurements. We perform polarimetric measurements on high-quality core-shell CdSe/CdS nanocrystals and demonstrate that they can be approximated by two orthogonal degenerated dipoles. Finally, we show that the orientation of a dipole can be inferred by polarimetric measurement, even for a dipole in the vicinity of a gold film, while in this case, the well-established defocused microscopy is not appropriate

Consequence of shape elongation on emission asymmetry for colloidal CdSe/CdS nanoplatelets

“…The orientation (Θ, Φ) of the 2D dipole is then normal to the plane containing the two orthogonal linear transitions (or the two σ + and σ -transitions). As described in [4,7,36], a linear polarization analysis allows us to retrieve information regarding the nature and orientation of the emitting dipole.…”

“…For a 1D dipole, in a polarimetry emission analysis [4], the intensity of the emission transmitted by a rotating polarizer along angle α can be expressed as I(α) = I min + (I max − I min )cos 2 (Φ -α) (Eq. (1)).…”

“…In both cases, polarized emission can be observed, with the degree of polarization depending of their orientation (with polarization degree higher for 1D dipoles). Analyses using polarimetric methods, sometimes combined with defocused imaging or decay curves, have demonstrated 2D-dipole behavior for spherical core-shell quantum dots [1][2][3][4] and dot-in-plate structures [5], and 1D-dipole behavior for nanorods [6] and dot-in-rods [7], with intermediate 1D+2D behavior for some structures [8,9]. These studies have found dipolar nature (1D or 2D) to be related both to the symmetry and degeneracy of the electron-hole transition dipole, and also to the shape of the nano-object, even when the Bohr radius of the exciton is smaller than the size of the nanoobject, a size difference that should made the dipolar transition insensitive to spatial confinement.…”

Probing the hot spot properties of semicontinuous gold films through the fluorescence polarization of CdSe/CdS colloidal nanocrystals

“…This result is compared to calculations for various NCs orientations. 24 The NC is then modeled with two incoherent dipoles perpendicular to the c-axis. The NC emits at 630 nm and is placed 10 nm above the surface with 25 nm gold thickness.…”

Спиновая Физика Экситонов В Коллоидных Нанокристаллах

“…Линейно поляризованный диполь часто назы-вают невырожденным одномерным диполем [97]. Состо-яния светлого экситона ±1 U,L поляризованы перпенди-кулярно к оси c и известны как вырожденные двумерные диполи [97][98][99]. Скорость спонтанной излучательной…”