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Al 2 O 3 :Eu 3+ (1%) samples were prepared by combustion, ceramic, and Pechini methods annealed from 400 to 1400 °C. XRD patterns indicate that samples heated up to 1000 °C present disordered character of activated alumina (γ-Al 2 O 3 ). However, α-Al 2 O 3 phase showed high crystallinity and thermostability at 1200–1400 °C. The sample characterizations were also carried out by means of infrared spectroscopy (IR), scanning electron microscopy (SEM) and specific surface areas analysis (BET method). Excitation spectra of Al 2 O 3 :Eu 3+ samples present broaden bands attributed to defects of Al 2 O 3 matrices and to LMCT state of O → Eu 3+ , however, the narrow bands are assigned to 7 F 0 → 5 D J , 5 H J and 5 L J transitions of Eu 3+ ion. Emission spectra of samples calcined up to 1000 °C show broaden bands for 5 D 0 → 7 F J transitions of Eu 3+ ion suggesting that the rare earth ion is in different symmetry sites showed by inhomogeneous line broadening of bands, confirming the predominance of the γ-alumina phase. For all samples heated from 1200 to 1400 °C the spectra exhibit narrow 5 D 0 → 7 F J transitions of Eu 3+ ion indicating the conversion of γ to α-Al 2 O 3 phases, a high intensity narrow peak around 695 nm assigned to R lines of Cr 3+ ion is shown. Al 2 O 3 :Eu 3+ heated up to 1100 °C presents an increase in the Ω 2 intensity parameter with the increase of temperatures enhancing the covalent character of metal–donor interaction. The disordered structural systems present the highest values of emission quantum efficiencies ( η ). CIE coordinates of Al 2 O 3 :Eu 3+ are also discussed. |
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