Optical Properties of the Type-II Core−Shell TiO₂@CdS Nanorods for Photovoltaic Applications

The well-known surface-functionalized method has been employed to synthesize TiO 2 @CdS core−shell nanorods using citric acid as a surface-functionalized agent. By varying the concentration of the citric acid, core−shell nanorods of core diameter 36 nm with different shell thickness (19−34 nm) were formed. The UV−visible absorption spectra of the core−shell nanorods show a red shift of the band edge of uncoated TiO 2, and the broadening of the absorption spectra is also observed with shell growth. Steady-state photoluminescence (PL) spectra of the core−shell nanorods give a new emission in the visible region and also red shift with the increasing shell thickness. Decay kinetics indicate that the average lifetime ⟨τ⟩ of the core−shell nanorods is larger than that of the uncoated TiO 2, and it varies from nanoseconds to picoseconds. The current−voltage ( I−V ) curves of the core−shell nanorods give a photocurrent density that is 212 times greater than the dark current density.