CsPbBr3 perovskite nanorods (NRs) are emerging as a new class of semiconductor nanomaterial with remarkable optical properties, such as high quantum fluorescence yields (FQYs) and tunable emission wavelengths. In addition, these materials display high emission anisotropy, making them potential candidates for applications that require oriented photon emission, such as luminescent solar concentrators and LCD backlights. However, unlike more well-established cadmium chalcogenide NRs, the origin of emission anisotropy is less well understood. To date, there are two major sources of emission anisotropy in semiconductor NRs: (1) classical dielectrics effects and (2) quantum confinement of electronic transition dipoles. Here, we measure the emission anisotropy of an ensemble of CsPbBr3 NRs and apply a dielectric model based on the dielectric constant of the NRs and their environment to analyze the interplay between electronic and dielectric contributions to their emission anisotropy. An excitation photoselection method was used to measure the emission anisotropy of NRs ensembles. The contribution of dielectric effects to the emission anisotropy of CsPbBr3 NRs was analyzed by modeling the NR as a dielectric prolate ellipsoid and calculating the electric field distribution inside the NR using the finite difference time domain (FDTD) method. Ensemble emission anisotropy measurements of NRs show an energy-independent anisotropy spectrum with a constant value close to 0.1. Moreover, the determination of the emission anisotropy of NRs based on the dielectric model reveals an anisotropy value close to 0.1, indicating the significant role of the dielectric effect on the obtained anisotropy. These results suggest that the emission anisotropy in CsPbBr3 NR is mainly due to the dielectric confinement of the optical electric field and not the result of quantum confinement of transition dipoles. These findings provide a fundamental understanding of the origin of emission anisotropy in perovskite NRs and inform possible strategies to control anisotropy in these materials by changing their dielectric environment for applications that require the emission of oriented photons.

Dielectric effects dictate the emission anisotropy in colloidal CsPbBr3 nanorods

ACS Spring 2022

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