Effect of oxygen on excitation spectra of AlN luminescence in the interband transition region

In this work, several samples of crystalline powders of AlN (unactivated) with the ma/olar oxygen concentration from 1.84 to 11.1% have been investigated. Their excitation spectra have been measured in the range from 5.5. to 14 eV. In these spectra, one may distinguish four broad bands with hνsub(max)=6.2, 7.0, 8.7, and 10.8 eV. As the oxygen content increases, the luminescence yield becomes highter over the entire excitation spectrum, because the concentration of luminescence centres increases simultaneously, but the band with hνsub(max)=8.7 eV increases much faster than the remaining three bands. This fast-growing band originates from the oxygen atoms that accumulate in the neighbouring lattice sites. It has been shown that the lattice of AlN permits such an arrangement of oxygen and aluminium atoms which differs but slightly from their mutual arrangement in the lattice of α-Al2O3. The energy position of the investigated excitation band with hνsub(max)=8.7 eV corresponds to the margin of the fundamental absorption by corundum. The observed band is attributed to the accumulations of oxygen atoms in the lattice, which, together with aluminium atoms in octahedral vacant sites, form a structure similar to a part of the corundum lattice