| 摘要 |
PROBLEM TO BE SOLVED: To improve sharpness of an image to improve an image characteristic by setting an average grain size of a phosphor in a lower layer portion abutting to a glass plate in a fluorescent layer smaller than that of a phosphor in an upper layer portion positioned on the opposite side of the glass plate. SOLUTION: A fluorescent layer 21 is formed in a structure where many phosphor particles are stacked, and a fluorescent layer 21a in a lower layer portion abutting to a glass plate 18 is formed of phosphor particles 22a with small average grain size. A fluorescent layer 21b in an upper layer positioned above the fluorescent layer 21a, namely, the fluorescent layer 21b on the opposite side of the glass plate 18, is formed of phosphor particles 22b with average grain size larger than that of the fluorescent layer 21a. Furthermore, thickness of the fluorescent layer 21a in the lower layer formed from the phosphor particles 22a with average grain size smaller than that of the fluorescent layer 21b in the upper layer is set thinner than that of the fluorescent layer 21b in the upper layer formed of the phosphor particles 22b with large average grain size.
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