Energy transfer and polarized emission in cadmium selenide nanocrystal solids with mixed dimensionality

Excited-state energy transfer from spherical green-light-emitting nanocrystals as donor to rod-shaped red-light-emitting nanocrystals as acceptor is shown to result in a predominant red fluorescence in mixed films. For this purpose red-light-emitting core-shell CdSe/CdS quantum rods with high fluorescence quantum yields Of eta(F) = 45 % were synthesized and used to create mixtures with green-light-emitting core-shell CdSe/CdS quantum dots eta(F) = 40 %). For this donor-acceptor combination the Forster distance is less than 6.6 nm and close to the sum of the diameters of the dots and rods. Hence, only quantum dots directly neighboring a quantum rod can efficiently participate in the energy transfer. A simple rubbing technique was used to uni-axially align the quantum rods dispersed in thin films of quantum dots. Such mixed films showed polarized red emission, while the absorption remains unpolarized.