Synthesis of Monodisperse PbS/CdS Colloidal Quantum Dots Emitting at Telecommunication Wavelengths with suppressed Auger Rates and Gain Threshold

Semiconductor nanomaterials that combine high near-infrared (NIR) photoluminescence efficiency and photostability are limited. Pb-chalcogenide colloidal quantum dots (CQDs), and particularly PbS CQDs, are promising candidates. Nevertheless, the practical implementation of PbS CQDs in optical devices faces intrinsic limitations due to the 8-fold degeneracy of the conduction and valence bands, leading to enhanced nonradiative Auger recombination, hindering applications such as lasing. Here, we focus on the synthesis and optical characterization of core-shell PbS/CdS CQDs emitting at telecommunication wavelengths (1500-1620 nm) with suppressed Auger rates. We synthesized three series of core/shell PbS/CdS CQDs from different-sized PbS cores via a cation exchange reaction. This approach produces PbS/CdS CQDs with high optical stability and narrow size distribution. Finally, we optically probed the nanocrystals with transient absorption, demonstrating suppressed Auger rates, increasing biexciton Auger lifetimes τ_<i>xx</i> up to 320 ps, while reducing the gain threshold of the system down to ⟨<i>N</i>⟩_gain≈ 1.7.