Ultrafast intrinsic excited state localization m 2D layered As2S3 by interlayer bond formation

Abstract

The family of two-dimensional (2D) layered materials with strong excitonic effect offers fascinating opportunities for studying excited state exciton behavior at 2D limit. While exciton dynamics in conventional 2D semiconductors (e.g. transition metal dichalcogenides) has been extensively studied, little is known about exciton properties and dynamics in 2D layered semiconductors with strong electron/exciton-phonon coupling. Here, by combining experimental and theoretical approaches, we reveal the intrinsic highly localized exciton (i.e. self-trapped exciton) in 2D layered As2S3, driven by strong exciton-phonon interaction. It is shown that photoexcited electron/hole charges in As2S3 localize spontaneously in ~110 fs, giving rise to large stokes-shifted and broad photoluminescence. An interlayer partial bond is formed between chalcogen atoms, triggering lattice distortion and carrier localization. Together with Urbach-Martienssen analysis, this study provides a comprehensive physical picture to understand the complex interplay between exciton and lattice dynamics in 2D semiconductors, which has strong implications to their optoelectronic properties and applications.

Transient Photoinduced Pb2+ Disproportionation for Exciton Self-Trapping and Broadband Emission in Low-Dimensional Lead Halide Perovskites

“…The broadband emission in these WLE perovskites has been commonly attributed to intrinsic self-trapped excitons (STEs), − ,− distinguishing them from conventional extrinsic defect emission dependent on sample doping and quality. , STEs, quasi-particles composed of localized excitons with deformed lattices, have been proposed in various materials, including condensed rare gases, organic molecule crystals, oxides, chalcogenides, and metal halides. − In low-dimensional perovskites, excitons are formed by the binding of electrons and holes by quantum and dielectric confinement effects. Meanwhile, both long- and short-range exciton–phonon coupling is enhanced due to the soft and polar lattice and reduced dimensionality, facilitating STE formation. , Despite considerable reports of broadband emission in low-dimensional perovskites, the exact electronic and structural nature of these STE species remains elusive, hindering the rational design of high-efficiency WLE materials. − …”

Harnessing Hot Carriers in Two-Dimensional Materials

“…Recently, atomically thin 2D semiconductor materials have shown promising potential in hot carrier physics and in devices. Compared to their 3D counterparts, 2D semiconductors exhibit enhanced many-body interactions due to reduced dielectric screening and quantum confinement, resulting in significant exciton binding energy (e.g., up to 500 meV for monolayer semiconductors) and ultrafast electron–electron scattering within femtoseconds. − Additionally, the 2D geometry and atomic flatness without dangling bonds guarantee high density of states and allow readily interfacing 2D semiconductors with charge extraction components to achieve ultrafast interfacial charge transfer within 100 fs. ,− The combination of ultrafast electron–electron scattering and interfacial charge transfer in 2D semiconductors suggests exciting potential to explore and realize efficient hot carrier harvesting. Indeed, with the help of powerful transient spectra, efficient hot carrier transfer from graphene and other 2D semiconductors before interband electron–electron scattering has been observed, and multiple exciton generation and transfer with high yield and low threshold have been reported in MoTe 2 and black phosphorus (BP). − In this Perspective, we highlight three primary directions: (1) hot electron harnessing from graphene; (2) hot electron transfer from 2D semiconductors; and (3) multiexciton generation in 2D semiconductors.…”