This paper reports the synthesis and characterization of Cr 3+ -doped alumina by the sol-gel non-hydrolytic methodology. The resulting sample was treated at different temperatures. X-ray diffraction revealed that the ruby phase emerged in the sample treated at 1100 o C, which was later confirmed by absorption bands correspondent to Cr 3+ ions allowed transitions at 4 A 2 → 4 T 1 , 4 T 2 , and forbidden at 4 A 2 → 2 T 1 , 2 E, observed by diffuse reflectance UV-Vis. The luminescence spectroscopy showed the intensity band at 694 nm in red region, characterized of the Cr 3+ ion. The peaks at 702 and 705 nm correspond to N 1 and N 2 lines, respectively, which arose from the second and fourth nearest-neighbor exchange-coupled pairs of chromium(III) ion, respectively, ascribed to high chromium(III) concentration. The Cr 3+ cluster formation was observed in electron paramagnetic resonance signal as discussed in this work. Nuclear magnetic resonance evidenced that the 27 Al symmetry changed in the samples treated between 900 and 1100 o C.
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