Spectral-kinetic study of self-trapping and multiplication of electronic excitations in Al2O3 crystals

The luminescence spectra and the excitation spectra of intrinsic (7.6 and 3.77 eV) and extrinsic emissions for alpha-Al2O3, Al2O3:Sc and Al2O3:Ga crystals have been measured by means of synchrotron radiation of 4-40 eV at 8 and 80 K. The luminescence of self-trapped excitons (7.6 eV) can be excited at the direct photocreation of excitons or at the recombination of electrons with unrelaxed holes. Fast intraband luminescence (tau<2 ns) has been detected in a spectral region from 2.5 to 6.5 eV. The absorption of one photon of 25-37 eV leads to the formation of two or three electron-hole pairs causing a sharp increase of the efficiency of extrinsic emission of Sc3+ (5.6 eV), Ga3+ (4.6 eV) and F+ centers (3.85 eV). (C) 1999 Elsevier Science BN. All rights reserved.