  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 exciton energy as well as to a decrease in 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 an
quasi-type-II or even type-II band offset for the nanoparticles. Furthermore,
we analyze the impact of strain on a model in which the spectral diffusion of
the fluorescence emission of these nanoparticles 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, while the correlation of both also
exhibits a steeper slope than for the unstrained system. For a given CdSe core
size, an increase in CdS-shell thickness decreases the possible ranges of
energy shift and squared wave function overlap without changing the slope of
their correlation. On the other hand, for a given nanoparticle overall
thickness, dot/rod systems with a small CdSe core exhibit the strongest
influenceability by surface charges.
