The reduction of cathodoluminescence efficiency of phosphors has been observed after bombarding with H+, H2+, He+, Ne+, N2, and A+ions having energies from 1 to 25 kev. Detectable deterioration could be observed after a bombardment of less than 10−9coul/mm2of ions (5×1011ions/cm2). The deterioration could be annealed out at temperatures between 450° and 700°C. Results indicate that light 25‐kev ions probably penetrate 0.1&mgr; to 0.2&mgr; into the phosphor.