THE 12-LINE 1.682EV LUMINESCENCE CENTER IN DIAMOND AND THE VACANCY-SILICON COMPLEX

Ab initio cluster methods are used to investigate vacancy-impurity com plexes in diamond. We assign the 1.682 eV, twelve-line optical band to a vacancy-Si complex which has a very unusual, possibly unique struct ure with a Si atom at the center of a split vacancy. The method also s uccessfully accounts for the 1.945, 2.156, and 2.985 eV optical transi tions in trigonal vacancy-N defects and estimates of radiative lifetim es are given.