Long-range resonance transfer of electronic excitations in close-packed CdSe quantum-dot solids

We show spectroscopically that electronic energy transfer in close-packed CdSe quantum-dot (QD) solids arises from dipole-dipole interdot interactions between proximal dots. We use cw and time-resolved photoluminescence to study electronic energy transfer in optically thin and clear, close-packed QD solids prepared from CdSe QD samples tunable from 17 to 150 Angstrom in diameter (sigma<4.5%). High-resolution scanning electron microscopy and small-angle x-ray scattering are used to build a well-defined structural model for the QD solids. In mixed QD solids of small and large dots, we measure quenching of the luminescence (lifetime) of the small dots accompanied by enhancement of the luminescence (lifetime) of the large dots consistent with electronic energy transfer from the small to the large dots. In QD solids of single size dots, a redshifted and modified emission line shape is consistent with electronic energy transfer within the sample inhomogeneous distribution. We use Forster theory for long-range resonance transfer through dipole-dipole interdot interactions to explain electronic energy transfer in these close-packed QD solids.