Alignment of Rod‐Shaped Single‐Photon Emitters Driven by Line Defects in Liquid Crystals

Abstract

We use arrays of liquid crystal defects, linear smectic dislocations, to trap semi-conductor CdSe/CdS dot-in-rods which behave as single photon emitters. We combine measurements of the emission diagram together with measurements of the emitted polarization of the single emitters. We show that the dot-inrods are confined parallel to the linear defects to allow for a minimization of the disorder energy associated with the dislocation cores. We demonstrate that the electric dipoles associated with the dotin-rods, tilted with respect to the rods, remain oriented in the plane including the smectic linear defects and being perpendicular to the substrate, most likely due to the dipole/dipole interactions between the dipoles of the liquid crystal molecules and the dot-in-rods ones. Using smectic dislocations, we can consequently orient nanorods along a unique direction for a given substrate, independently of the ligands' nature, without any induced aggregation, leading as well to a fixed azimuthal orientation for the associated dot-in-rods' dipoles. These results open the way for a fine control of nanoparticle anisotropic optical properties, in particular a fine control of single photon emission polarization.Control of single photon emitters is a major objective in the field of nanophotonics.[1] The synthesis of colloidal semiconductor inorganic nanocrystals having specific light-emission properties has been providing important advances in this field. In particular, recent developments in synthesis methodologies, fully compatible with standard nanofabrication technologies have enabled a superior 3 control on nanocrystals composition and morphology.Rod-shaped nanocrystals showing pronounced polarization, behaving as emitting linear dipoles, have been obtained. [2][3][4] The encapsulation of a spherical core into a rod-like shell [5] resulted in non-blinking inorganic single photon emitters, [6] hereafter referred to as dot-in-rods (DRs). Moreover it has been recently shown that, by increasing the thickness of the shell, it is possible to greatly suppress photoluminescence blinking and to improve DRs overall photo-stability, while keeping a low probability of multi-photon emission. [7] Such features are of primary importance when nanocrystalsare used in applications demanding a control of photons'polarization, such as coupling with complex photonic cavities [8][9] or quantum cryptography.[10] The control of the polarization of the emitted light also requires the capacity to control the particle orientation. Howevertechnologies aimed at guiding nanocrystal orientation at the single particle level are still poorly discussed in literature.Alignednanoparticleshave been obtained through mechanical rubbing, [11] short-range interactions [12][13] or patterned substrates. [14] Liquid crystal-like structures, composed of alarge number of elongated nanocrystalsassembled in multi-layers have also been evidenced on both solid substrates [15][16][17][18] and water films. [18][19][20] Orientation and positional ordering of CdS and CdSe...

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.…”

Trapping of gold nanoparticles within arrays of topological defects: evolution of the LSPR anisotropy

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“…To prepare the DHFLC cell, two inner surfaces of indium tin oxide (ITO) glass plates were washed with acetone twice and coated with a 0.5% polyvinyl alcohol aqueous solution ( M w = 80 000–110 000). After drying, the two ITO glass plates were rubbed in an antiparallel direction then separated by 3.2 µm spacers and sealed with epoxy resin on two sides of the cell …”