Colloidal PbSe Nanoplatelets of Varied Thickness with Tunable Optical Properties

In this work, we report a colloidal synthesis of atomically flat PbSe nanoplatelets (NPLs) of different thicknesses from 3 to 6 monolayers via cation exchange from the corresponding CdSe NPLs. In order to preserve the delicate structure of the NPLs, we performed the reaction at mild conditions using a temperature of 80 °C and lead bromide dissolved in oleylamine and octadecene as a Pb precursor. Cation exchange affected the size and the shape of the resulting NPLs depending on their thickness, i.e., the thinnest platelets (3 monolayers) underwent a partial degradation, although retaining their 2D structure, while the thicker ones were etched on their edges. We observed thickness-dependent near-infrared (NIR) photoluminescence (PL) with maxima ranging from 1330 to 1550 nm and quantum yields (PL QY) reaching 15%. The PbSe NPLs exhibited an excellent stability of the optical properties upon their storage in ambient atmosphere for several weeks, which we attribute to an efficient surface passivation with brom...