| 摘要 |
PROBLEM TO BE SOLVED: To provide a fluorescent display tube having a phosphor for a low energy electron beam excellent in a life characteristic without including Cd. SOLUTION: As a comparative example, an La2 O2 S:Eu phosphor wherein indium oxide is added as an electric conductive agent is used. Example 1 is obtained by mixing Ca(OH)<2> into the La2 O2 S:Eu phosphor of the comparative example followed by calcining it at 1,000-1,200 deg.C in air for 2 hours. Examples 2 to 7 are obtained by adding Mg, Sr, Ba, Be and Ca, respectively, into the phosphor of the comparative example using the almost the same procedure as that of the example 1. When experimenting on the phosphor actually equipping a fluorescent display tube with them, the degree of initial luminance is almost the same as that of the comparative example except that examples 1, 3 and 4 have luminances not less than 15% higher than the comparative example. The residual rates of luminance after turning on a light for 500 hours in any case are not less than 70% except that examples 6 and 5 show 35% and 55%, respectively, higher than 25% of the comparative example exhibiting a long life. The content of an additive capable of giving the effect is in a range of 0.001-15 wt.%. The diffused distance from the phosphor surface of the additive is at most 400Å.
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