This paper reports the synthesis and characterization of Cr3+-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 ºC, which was later confirmed by absorption bands correspondent to Cr3+ ions allowed transitions at 4A2 → 4T1, 4T2, and forbidden at 4A2 → 2T1, 2E, observed by diffuse reflectance UV-Vis. The luminescence spectroscopy showed the intensity band at 694 nm in red region, characterized of the Cr3+ ion. The peaks at 702 and 705 nm correspond to N1 and N2 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 Cr3+ cluster formation was observed in electron paramagnetic resonance signal as discussed in this work. Nuclear magnetic resonance evidenced that the 2727 Saltarelli, M.; Matos, M. G.; de Faria, E. H.; Ciuffi, K. J.; Rocha, L. A.; Nassar, E. J.; J. Sol-Gel Sci. Technol. 2015, 73, 283. Al symmetry changed in the samples treated between 900 and 1100 ºC.
Keywords:
ruby; EPR; NMR; sol-gel; luminescence