Comparative study of the luminescence of Al2O3:Ti and Al2O3 crystals under VUV synchrotron radiation excitation

Comparative study of the luminescence of Al2O3:C and Al2O3 crystals under synchrotron radiation excitation

“…The emission spectrum of undoped Al 2 O 3 crystal at 10 K under excitation by SR in the exciton range with an energy of 8.97 eV ( Fig.1a, curve 1) presents the superposition of the luminescence of F + and F centers in the bands peaked at 330 and 416 nm, respectively [2][3][4], and band peaked at 240 nm related to the exciton luminescence. The emission band at 240 nm (5.16 eV) is strongly shifted in the low-energy side with respect to the band at 7.6 eV of a self trapped exciton (STE) luminescence [5,8,9] and can be assigned to the emission of excitons localized around of the defects [9] or some trace impurities [12,13] in Al 2 O 3 host. Usually the energy structure of such localized excitons is similar to that of a STE in oxides [15].…”

“…The excitation spectrum of the exciton emission in the 240 nm band in Al 2 O 3 crystal ( Fig.2a, curve 1) shows sharp two-component peak with maxima at 8.81 and 9.005 eV. We suppose that the last band can be related to excitation of the intrinsic exciton emission of Al 2 O 3 host [5,9] The excitation spectrum of the exciton luminescence in the Al 2 O 3 :C crystal in the 290 nm band at 10 K (Fig.2a, curve 2) significantly differs from that in Al 2 O 3 crystal for the 240 nm band (Fig.2a, curve 1) and consists of other two intensive bands in the exciton range peaked at 8.58 and 8.83 eV. The structure of this spectrum, which is closer to that of the excitation spectrum of the F + center luminescence in Al 2 O 3 :C crystal in the same range (Fig.2b, curve 2), supports the conclusion that the emission in the 290 nm band is the luminescence of excitons localized around F + centers.…”

“…The emission spectrum of Al 2 O 3 :C crystal at 10 K under excitation by SR in the range of the interband transitions (13.6 eV) and the exciton range (8.88 eV) ( Fig.1a, curves 4 and 5 respectively) presents superposition of the luminescence of F + and F centers in the bands peaked at 324 and 413 nm, respectively, as well as the band peaked at 290 nm, related to the luminescence of excitons localized around oxygen vacancies [6,7,9]. The detailed comparison of the emission spectra of Al 2 O 3 and Al 2 O 3 :C crystals at 10 K (Fig.1a) shows, that (i) the maxima of the emission band of F + and F centers in Al 2 O 3 :C crystals are notably (about 5 nm) shifted in comparison with the positions of these band in Al 2 O 3 crystals; (ii) the excitons emission of Al 2 O 3 crystals in the 240 nm band is suppressed when the intensity of the emission of excitons localized around oxygen vacancies in the 290 nm bands increases.…”

“…The luminescent properties of undoped and Ti doped Al 2 O 3 crystals have been also investigated under high-energy VUV excitation [5][6][7][8][9]. At the same time, up to now we cannot find in the literature any results related to the VUV luminescent spectroscopy of Al 2 O 3 :C crystals or ceramics.…”

Luminescence Properties of Al2O3:Ti in the Blue and Red Regions: A Combined Theoretical and Experimental Study

“…Unlike the red one, this luminescence generated many theories, but no definitive proof has yet been established to certify its origin(s). Indeed, this emission was successively assigned to the presence of F centers (a neutral defect made of an oxygen vacancy with two trapped electrons), to Ti 4+ with a possible presence of a + II cation (e.g., Mg 2+ ). ,− …”