PURPOSE: To eliminate the adhesion of foreign material to an electrode, and to prevent the resubstituion of a nitride modifying layer by holding the inert gas atmosphere in the processing after forming the nitride modifying layer on the inner surface of a light emitting tube.
CONSTITUTION: A light emitting tube is formed with crash sealing parts 4 in both ends of a bulb made of quartz glass, and the inner surface of the bulb 2 is formed with a nitride modifying layer 3 over the whole surface facing to the discharging space. This modifying layer 3 is a surface layer formed by substituting nitrogen N for the oxygen component O2 in silica SiO2 forming quartz as the material of a light emitting tube. During the bonding process of an exhaust tube, the inert gas is flowed from an opening part of one end of the glass tube 20 toward an opening part of the other end. As the inert gas, nitrogen gas is used, and the modifying layer 3 formed at a part 22 to be formed with the inner surface of a discharging space. When heating is finished in this condition, the ends of the glass tube 20 are crashed for sealing, and a molybdenum foil 7 is sealed to each sealing part, and the modifying layer 3 is formed in the inner surface of the discharging space.
TAKITA KAZUO
NISHIZAWA MAKOTO
