The luminescence of insulating materials excited by an electron beam

The light emitted from polycrystalline yttria, sapphire, and ruby crystals under electron-beam excitation has been investigated in the 300-900 nm wavelength range. These experiments were performed in order to detect electroluminescence effects, whose occurrence might be indicative of the further breakdown of the dielectric. A typical behavior has been detected for UV-blue emissions, which are highly dependent on the excitation parameters and, therefore, on the space charge configuration inside the insulator. The origin of this cathodoluminescence is attributed to the relaxation of the polarization defects formed by the local strained sites attached to oxygen vacancies