PURPOSE: To keep the gas atomosphere for a long time during the barrium evaporation period, by applying the gas doped getter with the nitrogen gas discharge substance to further the substance having smaller temperature conduction rate and the mixture of the nitrogen gas discharge substance.

CONSTITUTION: To the getter material consisting of barrium-aluminum alloy and nickel, as the nitrogen gas discharge substance, for example, iron-germanium nitride and the mixture of this with silicon dioxide with sintering are added and mixed, forming the getter by filling then in one vessel with pressure. In this case, the temperature conductivity of silicon dioxide is remarkably made smaller than that of nickel which is one of the major component of the getter material, and it delays partly the production of nitrogen gas (in-tube pressure curve 8) which prevents the straight progress of barrium on the fluorescent screen, during the barrium evaporation period (barrium evaporation curve 9) in heating the getter, and it keeps the phenomenon in two steps and the formation of getter can effectively be made.