The polarised adsorption and cathodoluminescence associated with the 1.40 eV centre in synthetic diamond

Synthetic diamonds that are grown using nickel or a nickel alloy as the solvent-catalyst contain 1.40 eV centres which are strongly segregated in the (111) growth sectors. Absorption and cathodoluminescence measurements made using polarising optics show that the dipole moment of the centre is preferentially aligned with the (111) growth planes. The absorption and luminescence systems have a zero-phonon doublet at 1.4008 and 1.4035 eV, and, surprisingly, the high-energy component exhibits a much higher degree of polarisation than the low-energy line. Polarisation-dependent structure is also observed in the vibronic absorption and luminescence bands. The zero-phonon splitting is due to a splitting of the electronic ground state, and a speculative model is proposed that may form a basis for understanding the different polarisation behaviours of the two lines.