SPECTROSCOPIC STUDY OF COBALT-RELATED OPTICAL-CENTERS IN SYNTHETIC DIAMOND

This article presents evidence that cobalt forms a series of optically active defect centers in diamond grown by high-temperature, high-pres sure synthesis. Photoluminescence (PL) studies reveal that the newly o bserved vibronic systems with zero-phonon energies at 1.989, 2.135, 2. 207, 2.277, 2.367, and 2.590 eV appear only in samples grown using a c obalt-containing solvent-catalyst. Results of an annealing study, carr ied out in the temperature range 1500 to 1800 degrees C, establish tha t many of the new bands appear during the temperature regime of nitrog en aggregation. It is therefore proposed that nitrogen forms complexes with cobalt to produce optically active centers, in a manner analogou s to that of nickel point defects in diamond. Detailed radiative decay time measurements and temperature dependence measurements show that a ll but one of the bands which are here associated with nitrogen-cobalt complexes have long radiative decay times (similar to 100 mu s), and this again is a characteristic of the PL centers arising from nickel-n itrogen complexes. All of the vibronic bands observed by PL may also b e produced by electron-beam excitation (cathodoluminescence). In this case it is necessary to use a low beam current density (less than or e qual to 10 mA cm(-2)), otherwise the spectra are dominated by emission from optical centers with much shorter decay times (similar to 20 ns) . Only one vibronic band, with a zero-phonon line at 1.852 eV, has bee n detected in absorption measurements, and the center responsible for this system does not give rise to luminescence. (C) 1996 American Inst itute of Physics.