Investigation of the phonon spectra in CdSe/CdS nanoplatelets by raman spectroscopy

We report the phonon spectra of core/shell CdSe/CdS nanoplatelets with different shell thicknesses studied using Raman scattering. The nanoplatelets are rectangular colloidal nanocrystals, with thicknesses of core and shell layers of a few nanometers. The Raman spectra show features corresponding to the dominating longitudinal optical (LO) and surface optical (SO) phonon modes of the CdSe core in CdS shell located in the frequency regions of 200-210 and 250-290 cm^-1, respectively. As the shell thickness increases, the phonon modes reveal a frequency shift and a change in intensity. The frequency shift associated with a change in the stress state in the core and shell, as well as with confinement effects is discussed. The phonon mode intensities are determined by the thickness of the shell and the proximity to resonant Raman scattering conditions.