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

Colloidal CdSe nanoplatelets (NPLs) have substantial potential in light-emitting applications because of their quantum-well-like characteristics. The self-trapped state (STS), originating from strong electron-phonon coupling (EPC), is promising in white light luminance because of its broadband emission. However, achieving STS in CdSe NPLs is extremely challenging because of their intrinsic weak EPC nature. Herein, we developed a strong STS emission in the spectral range of 450-600 nm by building superlattice (SL) structures with colloidal CdSe NPLs. We demonstrated that STS is generated via strong coupling of excitons and zone-folded longitudinal acoustic phonons with formation time of similar to 450 fs and localization length of similar to 0.56 nm. The Huang-Rhys factor, describing the EPC strength in SL structure, is estimated to be similar to 19.9, which is much larger than that (similar to 0.1) of monodispersed CdSe NPLs. Our results provide an in-depth understanding of STS and a platform for generating and manipulating STS by designing SL structures.

Automated summary

A method for generating strong self-trapped state emission in CdSe nanoplatelets using superlattice structures is developed, through the coupling of excitons and phonons, providing a platform for a deeper understanding of the self-trapped state.