Few-Layer PbI₂ Nanoparticle: A 2D Semiconductor with Lateral Quantum Confinement

Inspired by the superior optoelectronic performances of various 2D semiconductors, their new compositions and structures are being actively pursued in order to foster novel fundamental physics and device applications. As a layered semiconductor with a direct bandgap, few-layer PbI₂ should have drawn much research attention due to their capability of emitting photons at short wavelengths of the visible spectrum. Here we chemically synthesize few-layer PbI₂ flakes and nanoparticles, which demonstrate unique exciton properties that have rare counterparts in other 2D semiconductors. For three layers and more, the single PbI₂ flakes can be utilized to show how the bandgap energy of a 2D semiconductor evolves with the changing layer thickness. The single PbI₂ nanoparticles are associated with an ultranarrow photoluminescence line width of ∼1 meV, thus reflecting the influence of lateral quantum confinement on the energy-level structures of a 2D semiconductor. The above findings mark the emergence of a potent 2D platform that is more than complementary to well-studied transition-metal dichalcogenide monolayers.