The absorption strengths of N3 centers in natural type-Ia diamonds, and in neutron-irradiated and post-annealed synthetic type-Ib diamonds, were measured. In type-Ib samples, an increase in absorption was observed during illumination with light for which hν was greater than 1.65eV. This behavior was not observed in type-Ia samples. The material recovered when the exciting light was removed. The effect was explained in terms of electron transfer between the negative charge state of the N3 center, and electron traps.

Y.Mita, H.Kanehara, Y.Nisida, M.Okada: Philosophical Magazine Letters, 1997, 76[2], 93-7