Zone-Folded Longitudinal Acoustic Phonons Driving Self-Trapped State Emission in Colloidal CdSe Nanoplatelet Superlattices

Abstract

Colloidal cadmium chalcogenide nanoplates are two-dimensional semiconductors that have shown significant application potential for light-emitting technologies. The self-trapped state (STS), a special localized state originating from strong electron-phonon coupling (EPC), is likewise promising for use in one-step white light luminance owing to its broadband emission line width. However, achieving STS in cadmium chalcogenide nanocrystals is extremely challenging owing to their intrinsically weak EPC nature. By building hybrid superlattice (SL) structures via self-assembly of colloidal CdSe nanoplates (NPLs), we demonstrate in this paper zone-folded longitude acoustic phonons (ZFLAPs), which differ from monodispersed NPLs. A broadband STS emission in the spectra range of 450-600 nm is thereby observed. Through femtosecond transient absorption and impulsive vibrational spectroscopy, we reveal that STS is generated in a time scale of approximately 500 fs. It is driven by strong coupling of excitons and ZFLAPs with a Huang-Rhys parameter of approximately 22.7. Our findings provide a novel foundation for generating and manipulating STS emissions by artificially designing and building hybrid periodic structures that are superior to single-material optimization.Ultrathin colloidal CdX (X = S, Se, Te) nanoplates (NPLs) with a uniform atomic thickness [1][2][3][4] form a new class of two-dimensional material. They have attracted considerable attention in past decades for their excellent optical properties, such as a narrow line width 4,5 due to strong quantum thickness confinement, a high luminescent quantum yield 6 due to minimization of surface traps, and large mode gain coefficients 7-9 due to suppressed Auger recombination. These remarkable optical properties, together with their cost-effective preparation and notable stability, have made colloidal CdX NPLs promising as optoelectronic materials that can be used in light-emitting

Self‐Trapped Excitons in 2D SnP2S6 Crystal with Intrinsic Structural Distortion

“…[ 26 ] Considering the high crystallinity of the crystal and uniqueness of the distorted octahedrons in the structure, we believe that the STEs in SnP 2 S 6 take responsibility for its special optical properties. [ 27 ] A simple energy band diagram shown in Figure 1g can be used to describe this unique phenomenon. In this material, photo‐excited FEs are converted into STEs with different self‐trapping depths through strong electron‐phonon coupling.…”

Carbonate-Ion-Mediated Photogenerated Hole Transfer to Boost Hydrogen Production

“…From the steady-state PL quenching result, significantly diminished PL signals were observed on InPS NS with an extra addition of the CO 3 2– or/and S 2– and SO 3 2– scavenger (Figure a), indicating the efficient photogenerated hole-transfer process with the help of these ions in the solution . Then, ultrafast transient absorption (TA) spectroscopy, a robust tool for tracking real-time charge carrier dynamics in nanosystems, , was used to study the charge carrier dynamics under light illumination. In detail, time-resolved pump-probe spectroscopy, in which a pump pulse of 350 nm and optical probe pulses from 450 nm to 800 nm, was applied and used to detect the TA signals in real time.…”

Assembly, Properties, and Application of Ordered Group II–VI and IV–VI Colloidal Semiconductor Nanoparticle Films

“…Sui et al observed broad photoluminescence in CdSe nanoplatelet stacks, which was red shifted from the photoluminescence of single particles ( Figure ). [ 276 ] They ascribed this feature to a self‐trapped state, which describes the trapping of an exciton by its strong interaction with lattice phonons. Transient absorption measurements reveal the formation of this state with few 100s femtoseconds and photoexcited electron paramagnetic resonance measurements yield a g ‐factor of 2, which is identical to the value of free electron in vacuum, thus suggesting a trapped hole.…”