Origin of Shape-Dependent Fluorescence Polarization from CdSe Nanoplatelets

Abstract

In this study, we report the shape dependence of fluorescence polarization from colloidal CdSe nanoplatelets (NPLs). Despite the symmetry of their cubic unit cell structure, CdSe nanocrystals grow into two-dimensional platelets in the presence of acetate precursors, and the resulting NPLs exhibit polarized emission. The amount of acetate salts introduced during the synthesis plays a critical role in controlling the lateral aspect ratio of CdSe NPLs. Specifically, the more the acetate hydrate presents, the more squarelike face of NPLs emerges. As a result, we achieved CdSe NPLs with varying lateral aspect ratios ranging from 1.1 to 4.5 in our experimental conditions. At the same thickness, CdSe NPLs with higher lateral aspect ratios exhibit higher fluorescence polarization. We analyzed the shape dependence by preparing films of CdSe NPLs dropcast under an electric field and measuring emission and absorption polarizations from CdSe NPL films of known orientation parameters. The emission polarization stays n...