| 摘要 |
PURPOSE:To obtain a long-afterglow blue phosphor having a high luminous efficacy and a long afterglow time, by incorporating a sulfide phosphor of a specific compositional formula containing CaS and Cu, and Li, Na or K. CONSTITUTION:A phosphor represented by the compositional formula: CaS:Cu (a mol%), X (X is at least one element selected from among Li, Na and K; and a is 0.05-0.5). The phosphor can be prepared by mixing at least one carbon ate etc. of a coactivating element selected from among calcium carbonate, copper oxide, lithium, sodium and potassium in predetermined proportions and calcining the mixture, e.g. in a hydrogen sulfide atmosphere. The long-afterglow blue phosphor exhibits an afterglow as long as 10msec or longer in terms of an afterglow time constant (pi1/10). Since the chromaticity coordinates can be varied to a considerable extent by varying the proportion of the compositional ratio, a (mol%),and the kind and concentration of the coactivating element, a desired color ranging from blue to bluish green can be exactly obtained as desired.
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