Exciton Formation and Quenching in a Au/CdS Core/Shell Nanostructure

An atomistic description is presented of the excited state dynamics in spherical Au/CdS core/shell nanocrystals up to a diameter of 15 nm. Au-core excited states are considered in a multipole plasmon scheme, whereas a tight-binding description combined with a configuration interaction approach is used to compute single electron–hole pair excitations in the CdS-shell. The electron–hole pair energy-shift and screening due to an Au-core polarization is found of minor importance. For the studied system, the energy transfer coupling can be identified as the essential core–shell interaction. Characterizing the CdS-shell excitons by atomic centered transition charges and the Au-core by its multipole plasmon moments, an energy transfer coupling can be introduced that gives a complete microscopic description beyond any dipole–dipole approximation and with values around 10 meV. Together with a considerable plasmon–exciton energy mismatch, these coupling values explain the measured 300 ps lifetime of shell excitons due to energy transfer to the Au-core