Near-Infrared Emitting Colloidal PbS Nanoplatelets: Lateral Size Control and Optical Spectroscopy

Two dimensional (2D) colloidal PbS nano platelets (NPLs) with a thickness of 1.8-2.8 nm have been synthesized using a single-molecule precursor approach with lead octadecylxanthate. The lateral dimensions were tuned by varying the reaction temperature, growth time, and capping ligands. Transmission electron microscopy and X-ray diffraction reveal that the NPLs have an orthorhombic crystal structure rather than the rocksalt phase usually reported for bulk and nanostructured PbS. The 1.8 nm thickness, in combination with the tunable lateral dimensions, results in a blue-shifted absorption peak at 71S-730 nm and a 48-68 nm narrow emission spectrum with a surprisingly small, 18 nm Stokes shift at room temperature. The fluorescence lifetime of these PbS NPLs is 2 orders of magnitude shorter than the typical lifetime in OD colloidal PbS quantum dots, highlighting the advantageous properties of colloidal 2D nanostructures that combine strong transversal with weak lateral confinement.