Zone-folded longnitude acoustic phonons driving self-trapped state emission in colloidal CdSe nanoplate superlattice

TL;DR

This study demonstrates that zone-folded longnitude acoustic phonons in colloidal CdSe nanoplate superlattices induce broadband self-trapped state emission, revealing a new method to control light emission in nanostructures.

Contribution

The paper introduces a novel hybrid superlattice structure that enables strong electron-phonon coupling and broadband emission in cadmium chalcogenide nanocrystals, overcoming intrinsic material limitations.

Findings

Zone-folded longnitude acoustic phonons observed in superlattices.

Self-trapped state emission occurs within 500 fs, driven by exciton-phonon coupling.

Huang-Rhys parameter as high as 22.7 indicates strong coupling.

Abstract

Colloidal cadmium chalcogenide nanoplates are two-dimensional semiconductors that have shown great application prospect for light-emitting technologies. Self-trapped state (STS), a special localized state originated from strong electron-phonon coupling (EPC), has great potential in one-step white light luminance owing to its broadband emission linewidth. However, achieving STS in cadmium chalcogenide nanocrystals is extremely challenging due to their intrinic weak EPC nature. By building hybrid superlattice (SL) structures via self-assembly of colloidal CdSe nanoplates (NPLs), we demonstrated an emergence of zone-folded longnitude acoustic phonons (ZFLAP) differ from monodispersed NPLs, and observed a broadband STS emission in spectra range of 450-600 nm. Through femtosecond transient absorption and impulsive vibrational spectroscopy, we revealed that STS is generated in time scale of ~500 fs and is driven by strong coupling of excitons and ZFLAPs with Huang-Rhys parameter as large as ~22.7. Our findings provide a new avenue for generating and manipulating STS emission by artificially designing and building hybrid periodic structures superior to single material optimization.