Orientation of luminescent excitons in layered nanomaterials

Abstract

In nanomaterials, optical anisotropies reveal a fundamental relationship between structural and optical properties. Directional optical properties can be exploited to enhance the performance of optoelectronic devices, optomechanical actuators and metamaterials. In layered materials, optical anisotropies may result from in-plane and out-of-plane dipoles associated with intra- and interlayer excitations, respectively. Here, we resolve the orientation of luminescent excitons and isolate photoluminescence signatures arising from distinct intra- and interlayer optical transitions. Combining analytical calculations with energy- and momentum-resolved spectroscopy, we distinguish between in-plane and out-of-plane oriented excitons in materials with weak or strong interlayer coupling-MoS₂ and 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA), respectively. We demonstrate that photoluminescence from MoS₂ mono-, bi- and trilayers originates solely from in-plane excitons, whereas PTCDA supports distinct in-plane and out-of-plane exciton species with different spectra, dipole strengths and temporal dynamics. The insights provided by this work are important for understanding fundamental excitonic properties in nanomaterials and designing optical systems that efficiently excite and collect light from exciton species with different orientations.

Bloch Surface Waves for MoS2 Emission Coupling and Polariton Systems

“…An additional pair of TiO 2 /SiO 2 (14 nm/16 nm) is deposited on top of the photonic crystal in order to adapt the BSW energy dispersion to the excitonic transition of the MoS 2 mono-and bi-layer. The MoS 2 transition dipole moment (of the lowest energy excited state) lies in the plane of the device [37], therefore the MoS 2 emitted photons experience the best coupling when using a TE-polarized BSW, as in the case under our investigation.…”

Engineering light emission of two-dimensional materials in both the weak and strong coupling regimes

“…It has been demonstrated that the PL from 2D MoS 2 originates solely from in-plane excitons [46]. Therefore, the PL emission of MoS 2 layers can be described by an isotropic distribution of incoherently radiating dipoles lying in planes parallel to the layer interfaces.…”

Multidimensional coherent optical spectroscopy of semiconductor nanostructures: a review

“…Also of interest are excitons in coupled multi-layer materials [109]. Biexciton binding energy, homogeneous linewidth, and coupling between excitonic species in layered GaSe [110], and exciton dephasing in layered InSe [111], have been recently measured using MDCS by Dey et al…”