Effect of thermal treatments and Co concentration on the structural and luminescent properties of sputtered TiO2:Co films



Thin films of Co-doped titania were grown at room temperature by rf reactive co-sputtering. A post-growth annealing procedure was carried out at 300, 450, and 750 °C in an inert argon atmosphere. The samples were studied using X-ray diffraction, micro Raman, UV–Vis, and photoluminescence (PL) spectroscopies. The properties of the films were analyzed as a function of the Co concentration and the annealing temperature. The as-grown films were amorphous; however, after a thermal annealing procedure the samples presented a Co-concentration-dependent transition to the anatase phase. In particular, the samples annealed at 300 °C showed a strong and broad PL signal that was quenched after exposure to an Ar+ laser beam (λ = 488.0 nm) focused through a microscope objective. The emission properties of the films have been ascribed to defects arising during the amorphous–anatase structural phase transition. It was also shown that the intensity and quenching rate of the PL depended upon the Co concentration and the annealing temperature.