The annealing of interstitial-related optical centres in type II natural and CVD diamond

Optical absorption bands in diamond, associated with the carbon interstitial, show annealing stages at temperatures below that at which the vacancy becomes mobile. These bands include the 1.86 eV, TR12, R11 and 5RL systems. Although the vacancy is not mobile, the intensity of the GR1 band, which is due to transitions at the neutral vacancy, does decrease by about 15-20% during annealing at these relatively low temperatures (typically 420-540 degrees C). In this paper we show that the 1.86 eV and R11 systems anneal out completely, concurrently with the "rapid" annealing of the GR1 band, and we attribute the behaviour to the migration of the interstitial to the vacancy, followed by mutual annihilation. The process follows first-order kinetics, with an activation energy of 1.68 +/- 0.15 eV. The intensities of the 1.86 eV and R11 absorption bands are closely correlated during this annealing, and it is possible that the R11 absorption is produced by transitions to excited states of the 1.86 eV centre. The 5RL and the TR12 absorption bands increase in intensity, following annealing at 420-540 degrees C, but their annealing behaviours are not simply related to those of the GR1 and 1.86 eV centres. (C) 1998 Elsevier Science S.A.