Excitons and Trions in One‐Photon‐ and Two‐Photon‐Excited MoS₂: A Study in Dispersions

Abstract

Herein, various dispersions of MoS obtained by means of liquid phase exfoliation are spectroscopically, (spectro-) electrochemically, and microscopically characterized. At the core of these studies are transient absorption assays. Importantly, small-angle X-ray scattering measurements are employed to corroborate the exfoliated character of the MoS flakes in dispersion, on the one hand, and to correlate the results with TEM, AFM, and Raman characterization in the solid state, on the other. It is, then, demonstrated that transient absorption spectroscopy responds sensitively not only to changes in the sample preparation but also to instrumental and environmental parameters. It is documented that the spectroscopic features and their underlying lifetimes are tuneable on the femto-, pico-, and nanosecond scales by changing, for example, the centrifugation speed, the pump fluence, or the temperature. In other words, transient absorption spectroscopy provides an in situ method to quantitatively characterize liquid dispersions of MoS without facing the problems of reaggregated samples due to their drying for microscopic assays. The most far reaching results stem from resonantly and nonresonantly changing the pump fluence to characterize either single- or multiple-excited-state species such as excitons, trions, and bi-/multiexcitons and to follow their formation and deactivation pattern.

Graphdiyne‐Based Flexible Photodetectors with High Responsivity and Detectivity

“…It is found that both values of τ 1 and τ 2 are independent of the wavelengths. The ultrafast relaxation times (<100 ps) of GDY have been found, which indicate the outstanding potential of GDY in photonics and optoelectronics among the mainstream 2D materials such as BP, [ 29 ] MoS 2 , [ 30 ] and GeSe. [ 25b ] This ultrafast relaxation times can be attributed to the phonon–phonon scattering and the fast relaxation processes of the photogenerated carrier.…”

“…[ 25b ] This ultrafast relaxation times can be attributed to the phonon–phonon scattering and the fast relaxation processes of the photogenerated carrier. [ 30 ] The ultrabroad ESA characteristics and ultrafast relaxation times of GDY demonstrate the great potential of GDY for applications in photonics and photoelectronics devices, such as PDs, high‐speed modulators, all‐optical switcher, and saturable absorbers.…”

Ping‐Pong Energy Transfer in Covalently Linked Porphyrin‐MoS2 Architectures

“…These dynamics resemble those already reported for exfoliated MoS 2 . [21] For 2, excited states of both components are observed to participate in the decay cascade ( Figure 5). Selective excitation into the Soret-band absorption of 2 affords a photoinduced absorption at l = 450 nm and ground-state bleaching of the bands at l = 617 and 679 nm.…”

Excited‐State Charge Transfer in Covalently Functionalized MoS2 with a Zinc Phthalocyanine Donor–Acceptor Hybrid

“…Based on UV/Vis assays, 1 possesses characteristic absorption features, the Soret band at 348 nm and Q bands at 613, 653, and 680 nm . In exfoliated MoS 2 , there are A and B excitonic transitions at 668 and 605 nm, respectively, followed by direct transitions from the valence to the conduction band at 456 and 374 nm (Supporting Information, Figure S5) . Focusing on 2 , the major absorption due to ZnPc at around 680 nm masks the excitonic A band of MoS 2 , while, in reverse, the excitonic B band of MoS 2 overshadows the ZnPc absorption centered at 613 nm (Figure a).…”