An annealing study of nickel point defects in high-pressure synthetic diamond

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Abstract
Results of an annealing study, carried out in the temperature range 1500–1900 °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 structure, which extends throughout the visible region of the absorption spectrum, and gives the previously bright‐yellow‐colored diamonds a rich golden‐yellow color, is observed. By carrying out the annealing sequence on diamonds grown using various solvent catalysts a correlation is found 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 possible natures are speculated on. It is found that the defect‐induced one‐phonon spectra of the diamonds examined may be satisfactorily decomposed into three components. To account for certain changes in the infrared spectra during the annealing sequences, and using previously reported results, it is proposed that one of these components may result from nitrogen in a positive charge state.