Influence of Interface-Driven Strain on the Spectral Diffusion Properties of Core/Shell CdSe/CdS Dot/Rod Nanoparticles

By combining an atomistic valence force field approach and calculations based on the effective-mass approximation, we investigate the influence of strain effects on the band alignment and general excitonic properties of core/shell CdSe/CdS dot/rod nanoparticles. We find that the inclusion of strain effects leads to an increase in the exciton energy as well as to a decrease in the electron and hole wave function overlap. Importantly, the native type-I band alignment of the CdSe/CdS material system is preserved and does not change into a quasi-type-II or even type-II band offset for the nanoparticles. Furthermore, we analyze the impact of strain on the spectral diffusion of the fluorescence emission of these nanoparticles, which is explained by migrating surface charges. Our calculations show that the addition of strain effects leads to increased energy shifts as well as larger changes in the squared electron and hole wave function overlap, whereas the correlation of both also exhibits a steeper slope than for the unstrained system. For a given CdSe core size, an increase in the CdS shell thickness decreases the possible ranges of the energy shift and squared wave function overlap without changing the slope of their correlation. On the other hand, for a given overall nanoparticle thickness, dot/rod systems with a small CdSe core exhibit the strongest influenceability by surface charges.