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 gF = 45 % were synthesized and used to create mixtures with green-light-emitting core–shell CdSe/CdS quantum dots (gF = 40 %). For this donor–acceptor combination the Förster 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 uniaxially align the quantum rods dispersed in thin films of quantum dots. Such mixed films showed polarized red emission, while the absorption remains unpolarized