| abstract |
A fluorescent substance is comprised of a praseodymium- activated yttrium and/or rare earth oxysulfide represented by the chemical formula, R 2(1-x) Pr 2x O₂S, wherein R stands for at least one member selected from the group consisting of Y, Gd, La, and Lu and x for a numerical value satisfying the expression, 5 x 10⁻⁵ ≦ x ≦ 1 x 10⁻², and the substance having a linear absorption coefficient of not more than 6.0 cm⁻¹ at 550 nm. Preferably the fluorescent substance contains PO₄ in an amount of not more than 100 ppm. Substances of improved luminous emission intensity can be produced for use in radiation detectors and in X-ray CT apparatus. |