Low Threshold Fabry–Pérot Mode Lasing from Lead Iodide Trapezoidal Nanoplatelets

Lead Iodide (PbI₂) is a layered semiconductor with direct band gap holding great promises in green light emission and detection devices. Recently, PbI₂ planar lasers are demonstrated using hexagonal whispering-gallery-mode microcavities, but the lasing threshold is quite high. In this work, lasing from vapor phase deposition derived PbI₂ trapezoidal nanoplatelets (NPs) with threshold that is at least an order of magnitude lower than the previous value is reported. The growth mechanism of the trapezoidal NPs is explored and attributed to the synergistic effects of van der Waals interactions and lattice mismatching. The lasing is enabled by the population inversion of n = 1 excitons and the optical feedback is provided by the Fabry–Pérot oscillation between the side facets of trapezoidal NPs. The findings not only advance the understanding of growth and photophysics mechanism of PbI₂ nanostructures but also provide ideas to develop low threshold ultrathin lasers.