| 摘要 |
PROBLEM TO BE SOLVED: To obtain the subject fluorescent substance having an approximately spherical shape, free from discoloration, high in luminous efficiency and comprising a rare earth element oxysulfide by subjecting raw materials for the fluorescent substance to a thermal plasma treatment. SOLUTION: This fluorescent substance comprises transparent spherical particles expressed by the formula: Ln2 O2 S:R (Ln is at least one kind of group 3A element selected from a group consisting of Y, La, Gd and Lu; R is a lanthanide element), having an average particle diameter of 0.5-15μm and a major axis/minor axis ratio of 1.0-1.5, contains particles having diameters of 0.01-0.2μm in an amount of 0.001-0.5wt.%, has relations of the inequalities: 0.31<=(x)<=0.33 and 0.31<=(y)<=0.33, wherein the body color of the fluorescent substance is expressed by a chromaticity coordinate [(x), (y)], and has a light reflectivity of >=95%. The spherical fluorescent substance expressed by the formula and obtained by melting raw materials in thermal plasma and subsequently quenching the melted product is preferably received in the inner vessel of a double vessel. The powder of a sulfide is received in the outer vessel so as to cover the inner vessel, and the received materials are preferably heated at 950-1300 deg.C in a non-oxidizing atmosphere.
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