Infrared Amplified Spontaneous Emission from Two-Dimensional PbS Nanoplatelets.

Colloidal PbS/PbCl2 core/shell nanoplatelets were synthesized via wet-chemical methods using lead oleate and lead chloride as lead precursors. The resulting heterostructures consist of a PbS core, a PbCl2 shell, and an intermediate layer of lead sulfochloride alloy. These nanoplatelets exhibit a photoluminescence quantum yield of approximately 20%, nearly an order of magnitude higher than that of unshelled PbS nanoplatelets. Cyclic voltammetry measurements reveal a type-I band alignment between the core and shell. Despite the presence of strong attractive biexciton Auger recombination, as observed in transient absorption spectroscopy, the nanoplatelets achieve amplified spontaneous emission at a low pump threshold of 76 μJ cm-2. Their large lateral dimensions support the spatial distribution of multiple excitons, including repulsive biexcitons, enabling efficient light amplification.