LUMINESCENCE STUDIES ON PZT:Eu~(3+) SOL-GEL THIN FILMS

摘要

PZT: Eu~(3+) sol-gel thin films and bulk samples were synthesized by sol-gel method. The crystalline structure (perovskite) was obtained in these materials by heat treatment at different temperatures. The temperature for the films was lower than that used in the bulk samples to obtain the perovskite-type phase. X-ray diffraction shows the presence of the perovskite phase in both kinds of materials. Emission and excitation studies of the impurity Eu~(3+) were made to determine its luminescence response. For PZT: Eu~(3+) thin films, the excitation spectra shows a broad band from charge transfer and narrow peaks due to the ~7F_0 → ~5L_6 and ~7F_1 → ~5D_3 transitions with λο=612 nm; and due to ~7F_0 → ~5L_6 and ~7F_0 → ~5D_2 with λο=650 nm. The films exhibit a PZT pyrochlore phase. The decays show two general components: a fast one and a slow one. The bulk samples do not have the PZT pyrochlore phase, but a tetragonal phase was detected. They show hypersensitive transitions as ~7F_0 → ~5D_2 (excitation) and ~5D_0 → ~7F_2 (emission). These transitions reveal the presence of Eu~(3+) in sites of low symmetry. In the bulk sample the luminescence decrease at 300℃, and disappear at higher temperature. It was recovered at 1000?. Instead, the thin film recovers its luminescence at 600℃. This inhibition of the luminescence could be associated wit the crystallite size formed in the samples. The PZT: Eu~(3+) thin films show several advantages in comparison to the bulk samples, as a short time of preparation, and a better perovskite phase obtained at lower temperature.