Separation of ultrafast photoexcited electron and hole dynamics in CdSe quantum dots adsorbed onto nanostructured TiO_2 films

摘要

The ultrafast photoexcited electron and hole dynamics of CdSe quantum dots (QDs) deposited onto nanostructured TiO_2 films were studied using an improved transient grating (TG) technique. By comparing the TG responses, measured in air and in a Na_2S solution (hole acceptor), we succeeded in separating the dynamic characteristics of photoexcited electrons and holes in the CdSe QDs. We found that charge separation in the CdSe QDs occurred over a very fast time scale from a few hundreds of femtoseconds in the Na_2S solution via hole transfer to S~(2-) ions to a few picoseconds in air via hole trapping.