Change of cathodoluminescence spectra of diamond with continuous irradiation of low energy electron beam of 20 kV

Radiation hardness is one of superior properties of diamond. High energy electron beam in the range of MeV is used to produce radiation damages such as vacancy and interstitial atoms. However, remarkable change of cathodoluminescence (CL) spectra of type II synthetic diamond was observed with irradiation of 20 kV electron beam, when electron beam current is as high as 1 μA. The 420 and 540 nm lines are created with the irradiation of the beam, and grow followed by fading. A 410 nm broad band is found to grow with the irradiation. On the other hand, a 485 nm line goes down, while the free exciton line does not change in its intensity. Intensities of the bands depend on growth sector of the diamond, and remain after stopping the irradiation. The behavior of the luminescence bands suggests that as-grown diamond contains several defects changeable with electron beam with subthreshold energy.