Orientation of Individual Anisotropic Nanocrystals Identified by Polarization Fingerprint

Abstract

The polarization of photoluminescence emitted from anisotropic nanocrystals directly reflects the symmetry of the eigenstates involved in the recombination process and can thus be considered as a characteristic feature of a nanocrystal. We performed polarization resolved magneto-photoluminescence spectroscopy on single colloidal Mn 2+ :CdSe/CdS core− shell quantum dots of wurtzite crystal symmetry. At zero magnetic field, a distinct linear polarization pattern is observed, while applying a magnetic field enforces circularly polarized emission with a characteristic saturation value below 100%. These polarization features are shown to act as a specific fingerprint of each individual nanocrystal. A model considering the orientation of the crystal c⃗ axis with respect to the optical axis and the magnetic field and taking into account the impact of magnetic doping is introduced and quantitatively explains our findings. We demonstrate that a careful analysis of the polarization state of single nanocrystal emission using the full set of Stokes parameters allows for identification of the complete three-dimensional orientation of the crystal anisotropy axis of an individual nanoobject in lab coordinates.

Optical Probing of Crystal Lattice Configurations in Single CsPbBr3 Nanoplatelets

“…Note that, while the peculiar orthogonal arrangement of the split triplet states in the CsPbBr 3 NPLs and their fixed alignment on the substrate facilitate the determination of the spatial orientation in our experiments, even more complicated experiments have been demonstrated to grant access to the 3D orientation of complex nanosize fluorescent objects. 39,40 While this correlation sufficiently describes the occurrence of case II and III emission patterns, emission with a single peak (case I) as observed for ∼10% of the NPLs cannot be explained in this picture. Similar single-emission-peak spectra have been reported in QDs before and usually showed strong linear polarization.…”

“…For the case III NPL shown in Figure e,f, the polarization angles of the a orth / c orth and b orth emission lines are 110 and 20°, respectively, showing the orientation of the NPL to be 20° (Figure S5, bottom). Note that, while the peculiar orthogonal arrangement of the split triplet states in the CsPbBr 3 NPLs and their fixed alignment on the substrate facilitate the determination of the spatial orientation in our experiments, even more complicated experiments have been demonstrated to grant access to the 3D orientation of complex nanosize fluorescent objects. , …”

High-Frequency EPR and ENDOR Spectroscopy of Mn2+ Ions in CdSe/CdMnS Nanoplatelets

“…The spin properties and magneto-optical effects in diluted magnetic semiconductors (DMS) are greatly modified by doping with magnetic impurities . Band-offset engineering and tunable magnetic exchange interactions were demonstrated in various magnetic/nonmagnetic semiconductor nanostructures, including colloidal quantum dots and NPLs. − Manganese is considered as an extremely informative magnetic impurity for electron paramagnetic resonance (EPR), since any of its charge states has paramagnetic properties. For Mn 2+ ions, which are characterized by a half-filled 3d 5 electron shell, the orbital angular momentum vanishes, that is, the S -state 6 S 5/2 is realized.…”