Synthetic diamonds have been grown from metal melts containing silicon, at high pressures and high temperatures. The absorption and photoluminescence spectra have been investigated in the temperature range 1.8–77 K. A 12-line fine structure is observed close to 1.682 eV, and this can be divided into three similar groups each containing four components. The relative strengths of the optical absorption for the three groups of lines are found to be the same as the ratio of the abundancies of the natural isotopes of silicon, ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, ${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}$, and ${}_{}{}^{30}{}_{}{}^{}\mathrm{Si}$, thus showing that the 1.682-eV center is related to silicon impurity. The changes in the relative intensities of the four component lines associated with ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ indicate that the center has two ground-state energy levels with a separation of 0.20 meV. The occupancies of the two excited-state levels of separation 1.07 meV tend to reach thermal equilibrium after optical excitation and before luminescence takes place. The relative transition probabilities for the transitions have been determined. The degeneracies of the ground-state levels are the same, and the degeneracies of the excited-state levels are also equal to one another. The behavior of the 1.682-eV defect after electron irradiation and subsequent heat treatment is described.

• Received 19 December 1994

DOI:https://doi.org/10.1103/PhysRevB.51.16681