In recent years, a great interest has been attracted on semiconductor nanomaterials, such as metal oxide semiconductors, II-VI semiconductors and silicon. Since the semiconductor namomaterials show very interesting physical properties depending on their sizes and have numerous potentials in applications such as photovoltaic energy conversion, photocatalysis, and gas sensors. For example, a great deal of attention has been devoted to photocatalysis and dye-sensitized solar cells (DSSC) made from TiO{sub}2 nanostructures [1,2]. It is known that the morphology and crystal structures of the TiO{sub}2 have great influences on the photocatalytic activity and solar cell efficiency, although the mechanisms are poorly understood. Very recently, narrow-band-gap II-VI semiconductor quantum dots (QDs), such as CdS, PbS and CdSe, have also been the subject of considerable interest for light harvesters as an alternative to organic dyes in the DSSCs [2-8]. The photoexcited carrier dynamics of TiO{sub}2 and semiconductor QDs, and the electron transfer processes between the sensitizers and TiO{sub}2 are important factors affecting the photocatalytic activity and solar energy conversion efficiency. Some studies have been reported on investigating these dynamics using transient absorption (TA) and time-resolved photoluminescence spectroscopy [8,9]. However, the dependences of the electron and hole relaxation processes on the morphology of the substrates and the electron transfer rates from the QDs to the substrates are still poorly understood and more investigations are necessary.
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