Synthesis and photoluminescence study of La1.8Eu0.2O3 coating on nanometric α-Al2O3

In this work the La1.8Eu0.2O3 coating on nanometric alpha-alumina, α-Al2O3@La1.8Eu0.2O3, was prepared for the first time by a soft chemical method. The powder was heat-treated at 100, 400, 800 and 1200 °C for 2 h. X-ray powder diffraction patterns (XRD), transmission electronic microscopy (TEM), emission and excitation spectra, as well as Eu3+ lifetime were used to characterize the material and to follow the changes in structure as the heating temperature increases. The Eu3+ luminescence data revealed the characteristic transitions 5D0 → 7FJ (J = 0, 1 and 3) of Eu3+ at around 580, 591 and 613 nm, respectively, when the powders were excited by 393 nm. The red color of the samples changed to yellow when the powder was annealed at 1200 °C. The decrease in the (5D0 → 7F2)/(5D0 → 7F1) ratio from around 5.0 for samples heated at lower temperatures to 3.1 for samples annealed at 1200 °C is consistent with a higher symmetry of the Eu3+ at higher temperature. The excitation spectra of the samples also confirms this change by the presence of a more intense and broad band at around 317 nm, instead of the presence of the characteristic peak at 393 nm, which corresponds to the 7F0 → 5L6 transition of the Eu3+. The lifetimes of the 5D0 → 7F2 transition of Eu3+ for the samples heat-treated at 100, 400, 800 and 1200 °C was evaluated as 0.57, 0.72, 0.43 and 0.31 ms, respectively.