Precise control over the photoluminescence(PL) of single quantum dots(QDs) is important for their practical applications. We show that the PL of individual Cd Se/Zn S core/shell QDs can be effectively enhanced and continuously modulated by electrochemically manipulating the electron transfer(ET) between the QDs and the attached redox-active ligands such as 2-mercaptoethanol(BME). We found that i) the ET from BME to the QDs' surface trap states suppresses the blinking of the QDs, ii) the ET from the QDs' conduction band to the oxidization product results in dimmed PL when BME is oxidized,and iii) further oxidization of BME results in a significant PL brightening. The single particle measurements help us unveil the important features hidden in ensemble measurements and understand the underlying mechanism of the PL modulation.The results also suggest a simple yet efficient method to produce bright and non-blinking QDs and offer opportunities for further development of high resolution fluorescent bioimaging and nanodevices.
