Colour centres in neutron irradiated aluminium oxy-nitride

Abstract

Aluminium oxy-nitride (9Al2O3.5AlN) has been neutron irradiated to fluences varying from 1018-1024 n m-2 (En>1 MeV) at 60 degrees C. The defect structures were studied by X-ray lattice parameter measurements and optical spectroscopy. The lowest neutron doses produced an anomalous volume expansion of 0.17% which was also reflected in a shift of the absorption edge to longer wavelengths. The exponential variation of the absorption edge with photon energy suggests that the 'edge' is the long wavelength side of an exciton band. The identification of two V bands with the intrinsic octahedral aluminium vacancy (2.225 eV) and the tetrahedral aluminium vacancy (3.15 eV), and their relative strengths after low neutron doses, suggested that the volume expansion may be associated with the octahedral aluminium vacancy centre. The oscillator strength of the two V bands was calculated to be 3*10-5. At higher neutron fluences the increase in lattice parameter and anion vacancy concentration showed good agreement with those found for equivalent doses in Al2O3. Comparison with the absorption spectrum of irradiated Al2O3 leads to the following assignment of anion vacancy centres to absorption bands in AlON:F-5.46 eV, F+-5.00 eV, FA-4.6 eV, F2-4.1 eV, F2+-3.68 eV.