Effect of CdS film thickness on the photoexcited carrier lifetime of TiO2/CdS core-shell nanowires

TiO2/CdS core-shell nanowires were synthesized using a simple thermal oxidation treatment of a Ti film, followed by O-2 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 hand edge. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3651340]