Ultrafast Optical Studies of Carrier Relaxation Dynamics in PbSe Nanoplatelets

Two-dimensional materials have attracted widespread interest due to their unique electrical, optical, and mechanical properties. Most of the two-dimensional materials currently available have a layered crystal structure, allowing for the efficient mechanical cleavage of bulk materials to isolate individual monolayers. The synthesis of new classes of two-dimensional materials with non-layered crystal structures remains challenging. Here we present optical studies of an emerging class of two dimensional materials, a colloidal suspension of thin lead selenide nanoplalets. Due to the large Bohr radius of lead selenide ($\sim$ 46 nm), our nanoplatles of size 30 x 30 x 2 nm exhibit the effects of quantum confinement in all three dimensions. Using transient absorption and time resolved photoluminescence measurements we characterize the dominant relaxation pathways to explore how asymmetric confinement influences the carrier dynamics. Potential applications of lead selenide nanostructures arising from their small bandgap, such as infrared detectors as well as photovolatics are discussed.