Long decay luminescent materials having improved long decay time and improved high brightness is represented by the formula as Sr.sub.0.9995 .about..sub.0.998 Eu.sub.0.0005 .about..sub.0.002)Al.sub.2 O.sub.4 .multidot.(Sr.sub.0.9995 .about..sub.0.998 Eu.sub.0.0005 .about..sub.0.002)O .multidot.n(Al.sub.1-a-b B.sub.b Dy.sub.a).sub.2 O.sub.3 in it a=0.0005.about.0.0002, b=0.0001.about.0.35, n=1.about.8 and the method for manufacturing the long decay luminescent materials is characterized in heating the raw materials as SrCo.sub.3, .alpha. type alumina, .gamma. type alumina, boron-containing compound, Eu.sub.2 O.sub.3 and Dy.sub.2 O.sub.3 gradually from 400.degree. C. up to 1250.degree. C..about.1600.degree. C. during 7.about.10 hours, firing it at 1250.degree. C..about.1600.degree. C. for 3.about.5 hours and then cooing it gradually from 1250.degree. C..about.1600.degree. C. down to 200.degree. C. during 7.about.10 hours and the heating, firing and cooling processes are all conducted under the condition of existence of carbon.