Influences of Thermal Annealing and X-ray Irradiation on Secondary Electron Emission and Cathodoluminescence Spectra of Alumina Materials

Rf-windows are used at the output portion of the klystrons to isolate vacuum and transmit the rf-power. Surface flashover of alumina ceramics limits the transmission power of microwaves. The surface flashover depends not only on the high secondary electron emission coefficients, but also on electronic states of oxygen vacancies existing adjacent to the ceramic surface. Secondary electron emission (SEE) coefficients and cathodoluminescence (CL) measurements were performed on alumina ceramics after annealing or x-ray irradiation. The experimental results revealed that (1) SEE coefficients increased and the intensity of CL-spectra corresponding to F+-center, which is one of oxygen vacancy states, decreased after annealing, and (2) the intensity of CL-spectra corresponding to F+-center decreased after x-ray irradiation.