Luminescence of free and self-trapped excitons in wide-gap oxides

Behaviour of the intrinsic emissions of 7.6. 3.45 and 3.6 eV in Al2O3, Y2O3 and Sc2O3, respectively, has been studied under a crystal excitation by 5- 35 eV photons at 8-80 K. In Al2O3 and Y2O3, electrons and holes do nor unde rgo transformation into a self-trapped state, while self-shrunk excitons ar e formed at the direct optical creation of excitons or at the recombination of electrons with holes under the conditions of a high excitation density. In line with the theoretical assumption made by Sumi, manifestations of th e photocreation of spatially correlated self-trapped d-electrons and p-hole s are revealed in the spectra of the tunnel phosphorescence of Sc2O3. (C) 2 000 Elsevier Science B.V. All rights reserved.