Surface charge control of quantum dot blinking

A characteristic property of colloidal semiconductor nanocrystal quantum dots (QDs) is their emission intermittency. Although a unifying theory of QD photoprocesses remains elusive, the importance of charged states is clear. We now report a new approach to directly study the role of surface charge on QD emission by adding metal ions to individual, core-only QDs immobilized in aqueous solution in an agarose gel. The CdTe QDs show very stable emission in the absence of metal ions, but a dramatic and reversible increase in blinking due to the presence of trivalent metal ions. Our results support a charge-separation model, in which the major blinking pathway is the surface trapping of electrons; transiently-bound metal ions close to the QD surface enhance this process