Efficiency of energy transfer from organic dye molecules to CdSe-ZnS nanocrystals: nanorods versus nanodots.

We report on comparative experimental study of FRET efficiency in two different systems: organic dye molecules (donors) and CdSe-ZnS core-shell nanodots or nanorods (acceptors). Fluorescein isothiocyanate was bound chemically to the surface of nanocrystals using cysteine as a linker and the conjugates were embedded into the polymeric films. Contrary to intuitive presumptions based on the order of magnitude larger molar absorption coefficient for nanorods, the experiment demonstrated almost equal efficiency in the energy transfer from FITC to nanorods and nanodots. This effect is attributed to a distance-limited region of nanorod to which an efficient FRET from dye molecule can be achieved. These results may pave the way to hybrid materials with FRET efficiency controlled by the geometry of nanocrystals.