Two types of luminescence blinking revealed by spectroelectrochemistry of single quantum dots

The phenomenon of fluorescence intermittency (blinking between ON/OFF states) has been observed for both naturally occurring fluorophores (such as organic dyes and biomolecules) and artificial nanostructures (such as carbon nanotubes and semiconducting nanocrystal quantum dots). This study aims to resolve the long-standing controversy surrounding the origin of photoluminescent blinking in semiconductor nanocrystals, also known as quantum dots. Researchers usually evoke the Auger, or A-type, mechanism in which a separation of charges yields to the OFF state, but recent observations have raised doubts about this explanation. Galland et al. describe a second mechanism (called B-type) in which an excited, or hot, electron becomes trapped in the shell for a time before being released to the emitting core. By controlling various parameters, such as applied voltage potential and shell thickness, the authors can control the frequency of blinking, or suppress it completely.