Characterization of electron transfer from CdSe quantum dots to nanostructured TiO2 electrode using a near-field heterodyne transient grating technique

The ultrafast carrier dynamics of the CdSe QDs adsorbed on a nanostructured TiO2 electrode and on a glass substrate were studied using a near-field heterodyne detection transient grating (NF-HD-TG) method. Two decay processes were observed in the TG responses. The fast decay time constants tau(1) were the same (2.3 ps) for these two kinds of substrates, corresponding to the photoexcited hole relaxation in the CdSe QDs. However, the slow decay time constants tau(2) were very different for these two kinds of substrates, reflecting the photoexcited electron relaxation (i.e., trapping and/or transfer). Since no electron transfer from the CdSe QDs to the glass substrate could occur, we could estimate the electron transfer rate from the CdSe QDs into the nanostructured TiO2 electrode to be approximately 5.4 x 10(9) s(-1) using the values of tau(2) detected for these two kinds of substrates. (C) 2007 Elsevier B.V. All rights reserved.