Phonons in Core-Shell CdSe/CdS Nanoplatelets Studied byVibrational Spectroscopies

In this work, the phonon spectra of core/shell CdSe/CdS nanoplatelets with different shell thicknesses were studiedusing IR and Raman spectroscopies. Nanoplatelets are rectangular plates, with lateral dimensions of tens of nanometers andthicknesses of core and shell layers of a few nanometers. Longitudinal optical (LO) and surface optical (SO) phonon modes in theCdSe core and the CdS shell dominate in the Raman spectra at frequencies of approximately 200-210 and 250-300 cm-1,respectively, while transverse optical (TO) modes in the nanoplatelets (NPLs) are active in the IR reflection/absorption spectra near170 and 240 cm-1. The LO modes can be additionally activated in the IR spectra measured at an oblique angle of light incidencethat provides a component of the electricfield perpendicular to the surface. As the shell thickness increases, the phonon modesreveal frequency shifts of optical modes, which are explained in terms of the stress state in the core and shell, as well as the influenceof phonon confinement. Low-frequency peaks of bare CdSe and core-shell CdSe/CdS platelets were observed in the Ramanspectra, and their frequencies were compared with both literature data and the results of calculations within a two-phase model.

Automated summary

The phonon spectra of core/shell CdSe/CdS nanoplatelets with different shell thicknesses were studied, revealing frequency shifts of optical modes as the shell thickness increases, which can be explained in terms of the stress state in the core and shell, as well as the influence of phonon confinement.