Engineering Optical Activity of Semiconductor Nanocrystals via Ion Doping

Abstract

Controlling the strength of enantioselective interaction of chiral inorganic nanoparticles with circularly polarized light is an intrinsically interesting subject of contemporary nanophotonics. This interaction is relatively weak, because the chirality scale of nanoparticles is much smaller than the optical wavelength. Here we theoretically demonstrate that ion doping provides a powerful tool of engineering and enhances optical activity of semiconductor nanocrystals. We show that by carefully positioning ionic impurities inside the nanocrystals, one can maximize the rotatory strengths of intraband optical transitions, and make them 100 times larger than the typical rotatory strengths of small chiral molecules.

Completely Chiral Optical Force for Enantioseparation

“…The considered example shows that the complete enantioseparation on a submillimeter scale over times of a few hundreds of seconds requires chiral forces of the order of 10 −16  N. Such forces are unattainable for small molecules, with typical rotatory strengths of about 10 −45  J cm 3  33, but can be achieved at moderate optical powers for specifically designed chiral nanoparticles with high χ ″. Indeed, if the molecules interact with 600-nm photons of energy 3.3 × 10 19  J, then cχ ″ ~ 3 × 10 −27  cm 3 and the light of intensity 1 MW/cm 2 produces a chiral force of about 10 −24  N. In order to achieve forces as high as 10 −16  N with the same light intensity, one needs to have χ ″ that is eight orders of magnitude larger.…”

Intraband optical activity of semiconductor nanocrystals

“…In this article we present a review of three theoretical models, which use this theory to describe chiroptical properties of real chiral nanocrystals. We show how to calculate intraband optical activity induced by ionic impurities, screw dislocations, and nanocrystal shape . Our results indicate that even small perturbations of the nanocrystal electronic subsystem can produce intraband optical activity exceeding that of typical chiral molecules by a factor of 100 to 1000.…”

“…The crystal lattice can be chirally distorted during the nanocrystal growth by screw dislocations and Eshelby twists . Introduction of various impurities into a nanocrystal also distorts its crystal lattice and can break the nanocrystal's mirror symmetry . Optical activity can be induced by chiral ligands attached to the nanocrystal's surface and the resulting coupling between the nanocrystal's and ligand's electronic subsystems .…”

“…[12][13][14][15][16] Introduction of various impurities into a nanocrystal also distorts its crystal lattice and can break the nanocrystal's mirror symmetry. 17 Optical activity can be induced by chiral ligands attached to the nanocrystal's surface and the resulting coupling between the nanocrystal's and ligand's electronic subsystems. [18][19][20][21] Chirality of a crystal lattice usually leads to a chirality of shape, which also contributes to the optical activity of the nanocrystal.…”

Ligand-induced chirality and optical activity in semiconductor nanocrystals: theory and applications

“…(iv) Chiral defects: chiral surface and structural defects can be produced during the synthesis of NPs in the presence of chiral ligands, such as it has been done for aqueous penicillamine capped CdS QDs [55]. (v) Spontaneous chiral defects: NPs can be synthesized with spontaneous chiral surface and structural defects (e.g., screw dislocations [56,57] and dopant ions [58]) even without the presence of chiral ligands and can then be extracted from an achiral mixture by enantioselective phase transfer [40,59,60]. (vi) Ligand-induced chirality (LIC): optical activity may be induced in colloidal NPs through interaction of NPs with chiral ligands, such as cysteine or penicillamine [27,[61][62][63].…”