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

In this work the La{sub 1.8}Eu{sub 0.2}O{sub 3} coating on nanometric alpha-alumina, {alpha}-Al{sub 2}O{sub 3}atLa{sub 1.8}Eu{sub 0.2}O{sub 3}, was prepared for the first time by a soft chemical method. The powder was heat-treated at 100, 400, 800 and 1200 deg. C for 2 h. X-ray powder diffraction patterns (XRD), transmission electronic microscopy (TEM), emission and excitation spectra, as well as Eu{sup 3+} lifetime were used to characterize the material and to follow the changes in structure as the heating temperature increases. The Eu{sup 3+} luminescence data revealed the characteristic transitions {sup 5}D{sub 0} {sup {yields}} {sup 7}F {sub J} (J = 0, 1 and 3) of Eu{sup 3+} 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 deg. C. The decrease in the ({sup 5}D{sub 0} {sup {yields}} {sup 7}F{sub 2})/({sup 5}D{sub 0} {sup {yields}} {sup 7}F{sub 1}) ratio from around 5.0 for samples heated at lower temperatures to 3.1 for samples annealed at 1200 deg. C is consistent with a higher symmetry of the Eu{sup 3+} at higher temperature. The excitation spectra of the samples alsomore » 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 {sup 7}F{sub 0} {sup {yields}} {sup 5}L{sub 6} transition of the Eu{sup 3+}. The lifetimes of the {sup 5}D{sub 0} {sup {yields}} {sup 7}F{sub 2} transition of Eu{sup 3+} for the samples heat-treated at 100, 400, 800 and 1200 deg. C was evaluated as 0.57, 0.72, 0.43 and 0.31 ms, respectively.« less