The 1.945eV optical centre was produced in type Ib diamond by radiation damage and annealing at approximately 800C. The author reports that H3 (2.463eV) centres, characteristic of irradiated and annealed type Ia diamond, were created by heating an irradiated type Ib diamond to temperatures where nitrogen aggregation occurs. This observation strongly supported the models previously proposed for the H3 and 1.945eV centres. The rate of nitrogen aggregation appeared to be considerably faster than that reported previously for non-irradiated samples.

Migration of Nitrogen in Electron-Irradiated Type Ib Diamond. Collins, A.T.: Journal of Physics C, 1978, 11[10], L417-22