Bright Type II Quantum Dots.

It is a paradigm that the excitonsplitting characteristics oftype II quantum dots (QDs) result in low quantum yield materials.However, reported herein is the synthesis of ZnSe/CdS/ZnS type IIQDs with quantum yields as high as 61%. Most interesting is the factthat the enhancement in brightness is due to an increase in the radiativerate, rather than the suppression of surface trap-related nonradiativeprocesses, which was found to be minimal. These QDs have been water-solubilizedusing two different methods and retain a substantial fraction of theirbrightness. The water-soluble type II QDs were conjugated to a dyeto examine their potential as fluorescence resonance energy transfer(FRET) donors. A significant FRET efficiency of 61 ± 3% was measuredusing time-correlated single photon counting, which demonstrates thepotential for these materials to be used in FRET-based chemical andbiological sensing applications. [ABSTRACT FROM AUTHOR]