Vacancy-related centers in diamond

Abstract

It is established that vacancies in diamond migrate, during annealing, primarily in their neutral charge state, with an activation energy of 2.3±0.3 eV. Negative vacancies are destroyed by first converting to neutral centers in a reversible charge transfer process. In relatively pure diamonds (type IIa) and in diamonds (type I) containing large concentrations of nitrogen, effectively all the vacancies in the samples after irradiation can be accounted for in their neutral (${\mathit{V}}^0$) and negative (${\mathit{V}}^{\mathrm{-}}$) charge states. In nitrogen-rich diamonds, the vacancies are predominantly trapped during annealing at the nitrogen. From the annealing data we derive the relative oscillator strengths of the main absorption bands of ${\mathit{V}}^0$, ${\mathit{V}}^{\mathrm{-}}$, and of one vacancy combined either with a single N atom, a pair of N atoms, or the larger ‘‘B’’ aggregate of nitrogen. In the absence of the intrinsic nonradiative decay channels of luminescence from ${\mathit{V}}^0$, we show that the radiative decay time would be 35±7 ns. In common natural (‘‘type IaA’’) diamonds, variations of absorption linewidths during annealing imply that about 40% of the vacancies are created within a few atomic sites of the nitrogen impurity, and direct observation confirms that vacancy production is enhanced in these diamonds. About half the vacancies, including those created near the nitrogen, anneal at each temperature about 12 times faster than those vacancies whose creation is not correlated with the nitrogen.