AN ANNEALING STUDY OF NICKEL POINT-DEFECTS IN HIGH-PRESSURE SYNTHETICDIAMOND

Results of an annealing study, carried out in the temperature range 15 00-1900-degrees-C, of nickel-related optical centers in high-pressure synthetic diamond are presented. It is established that the well-known 1.883 and 2.51 eV systems anneal out during the temperature regime of nitrogen aggregation and the concurrent growth of an array of structu re, which extends throughout the visible region of the absorption spec trum, and gives the previously bright-yellow-colored diamonds a rich g olden-yellow color, is observed. By carrying out the annealing sequenc e on diamonds grown using various solvent catalysts a correlation is f ound between preanneal 1.883 eV absorption and maximized absorption of some of the annealed structure. From the results it is proposed that centers associated with nickel and nitrogen are produced and their pos sible natures are speculated on. It is found that the defect-induced o ne-phonon spectra of the diamonds examined may be satisfactorily decom posed into three components. To account for certain changes in the inf rared spectra during the annealing sequences, and using previously rep orted results, it is proposed that one of these components may result from nitrogen in a positive charge state.