A comparative study demonstrates strong size tunability of carrier-phonon coupling in CdSe-based 2D and 0D nanocrystals

Abstract

In a comparative study we investigate the carrier–phonon coupling in CdSe based core-only and hetero 2D as well as 0D nanoparticles. We demonstrate that the coupling can be strongly tuned by the lateral size of nanoplatelets, while, due to the weak lateral confinement, the transition energies are only altered by tens of meV. Our analysis shows that an increase in the lateral platelet area results in a strong decrease in the phonon coupling to acoustic modes due to deformation potential interaction, yielding an exciton deformation potential of 3.0 eV in line with theory. In contrast, coupling to optical modes tends to increase with the platelet area. This cannot be explained by Fröhlich interaction, which is generally dominant in II–VI materials. We compare CdSe/CdS nanoplatelets with their equivalent, spherical CdSe/CdS nanoparticles. Universally, in both systems the introduction of a CdS shell is shown to result in an increase of the average phonon coupling, mainly related to an increase of the coupling to acoustic modes, while the coupling to optical modes is reduced with increasing CdS layer thickness. The demonstrated size and CdS overgrowth tunability has strong implications for applications like tuning carrier cooling and carrier multiplication – relevant for solar energy harvesting applications. Other implications range from transport in nanosystems e.g. for field effect transistors or dephasing control. Our results open up a new toolbox for the design of photonic materials.