Efficient Infrared Emission of Colloidal PbSe Nanoplatelets by Lateral Size Control

Colloidal two-dimensional (2D) lead chalcogenide nanoplatelets (NPLs) represent highly interesting materials for near- and short wave-infrared applications including innovative glass fiber optics exhibiting negligible attenuation. In this work, we demonstrate a direct synthesis route for 2D PbSe NPLs with cubic rock salt crystal structure at low reaction temperatures of 0 °C and room temperature. A lateral size tuning of the PbSe NPLs by controlling the temper-ature and by adding small amounts of octylamine to the reaction leads to excitonic absorption features in the range of 800 – 1000 nm (1.6 – 1.3 eV) and narrow photoluminescence (PL) seamlessly covering the broadband infrared spec-tral window of 900 – 1450 nm (1.4 – 0.9 eV). The PL quantum yield of the as-synthesized PbSe NPLs is more than doubled by a postsynthetic treatment with CdCl2 (e.g. from 14.7 % to 37.4 % for NPLs emitting at 980 nm with a FWHM of 214 meV). An analysis of the slightly asymmetric PL line shape of the PbSe NPLs and their characterization by ultrafast transient absorption and time-resolved PL spectroscopy reveal a surface trap related PL contribution which is successfully reduced by the CdCl2 treatment from 40 % to 15 %. Our results open up new pathways for a direct synthesis and straightforward incorporation of colloidal PbSe NPLs as efficient infrared emitters at technologi-cally relevant telecommunication wavelengths.