PURPOSE: To improve the luminance of a fluorescent substance, excitable with slow electron rays, and used for fluorescent display tubes, etc., by bringing metallic zinc into contact with a fluorescent substance, and irradiating the fluorescent substance with fast electron rays at such a level as to recoil the zinc atom.

CONSTITUTION: For example, a fluorescent substance 2 of ZnO:Zn is placed on a quartz glass plate 1, and a metallic zinc plate 3 having 0.2mm thickness is further placed thereon. The zinc plate 3 is then irradiated with fast electron rays accelerated in an electron ray accelerator from above at 7 MeV and 5×1017 electrons/cm2 intensity.