The red luminescence spectrum of brown diamonds: uniaxial-stress measurements

Abstract

Natural brown diamonds that emit yellow luminescence under 3.40 eV (365 nm) excitation are known to exhibit also a red luminescence band when excited with 2.69 eV (460 nm) radiation. Four zero-phonon red-luminescent lines have been studied under uniaxial stress. One of them, at 2.145 eV, believed to be the origin of the major vibronic progression known as the red band, is found to be a transition between A states at a monoclinic I centre. The other lines at 2.133, 2.156 and 2.166 eV are shown to be transitions between A and B states at monoclinic II centres, with the C2 point group. It is the first time that centres with this point group have been reported in diamond. The authors suggest that a relationship between the centres giving rise to the yellow and to the red luminescent bands, by comparison of their phonon sidebands, symmetries, responses to stress and zero-phonon energies.