Nano Lett.http://doi.org/hvt (2012)

Semiconductor nanocrystals have the potential to be used in optoelectronic devices, like solar cells or thermoelectric components. Scientists are trying to improve their electrical conductivity by adding charges to them. In bulk semiconductors, additional charges are usually provided by introducing impurity atoms, or dopants, but the task of repeating this procedure with nanometre-size specimens has proved challenging. When Ayaskanta Sahu and colleagues added silver atoms to CdSe nanocrystals they got more than they bargained for. For just two silver atoms in each nanocrystal they observed an unexpected tenfold enhancement of the fluorescence. Based on previous results reporting fluorescence enhancement by positive ions, the team suggested that at low concentration the silver atoms ionize and release electrons in the nanocrystals. The suggestion was confirmed by electrical measurements that showed an electron-enhanced conductivity. Although understanding the exact mechanism will require more work, the demonstration of electron doping represents a milestone in itself.