It was noted that an absorption band at 1.885eV was typical of N-containing high-pressure synthetic crystals which had been grown by using a Ni catalyst. Uniaxial stress measurements were carried out on the absorption zero-phonon lines and it was shown that the defect where this system occurred had rhombic symmetry. The system exhibited zero-phonon lines at 1.885, 1.907 and 1.915eV. It was shown that they corresponded to electric dipole transitions from a common Al ground state and into three B1 excited states at a C2v center. Evidence was found for the presence of another state, which was thought to lie 0.005eV below the ground state. Transitions from this state, which were dipole forbidden, became allowed via stress-induced mixing with the ground level; thus permitting the identification of the stress-induced lines with transitions from A2 and into B1 excited states. It was suggested that this absorption band occurred at a Ni-N complex with C2v symmetry.

M.H.Nazaré, L.M.Rino, H.Kanda: Materials Science Forum, 1995, 196-201, 73-8