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TiO2/CdS core-shell nanowires were synthesized using a simple thermal oxidation treatment of a Ti film, followed by O2 plasma treatment and CdS coating via low-cost chemical bath deposition. The 5 and 20 nm thick CdS films were uniformly coated onto TiO2 nanowires using 200 and 40 ml aqueous solvent, respectively. Time-resolved photoluminescence (PL) measurements on the TiO2/CdS (5 nm) nanowires showed a remarkably increased PL lifetime of 420 ps compared with the 60 ps of the TiO2/CdS (20 nm) nanowires. This result can be attributed to the enhanced electron-hole separation due to the more upshifted quantized electron energy levels of the 5 nm thick CdS film with respect to the TiO2 conduction band edge.

We studied both cw and time-resolved photoluminescence of colloidal CdSe/ZnS core-shell quantum dots capped with chemical ligands. For the trioctylphosphine oxide capped CdSe/ZnS QDs, both the luminescence intensity and lifetime were found to be increased with increasing temperatures, which can be explained by the thermal activation of the carriers trapped at shallow trapping centers. After the ligand exchange into 3-mercaptopropionic acid, the non-radiative recombination rate was increased and the luminescence efficiency was decreased at room temperature. When the QDs were employed in photovoltaic devices, photocurrent was found to be increased after the ligand exchange. The improved photocurrents observed in photovoltaic devices can be explained by the improved tunnelling probability between the neighbouring QDs

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