NEW MATERIAL:A substance of formula (A is Mg, Sr or Ba; MI is Dy, Sm, Lu, Bi, Cu, Eu, Ce or La; alpha and beta are a molar ratio of the concentration of each activating agent to the matrix, ranging from 1X10-6 to 1X10-1; x is a compounding ratio of 0-1X10-1). USE:A highly bright fluorescent substance useful for display cathode-ray tubes. The present fluorescent substance causes no environmental pollution and film- burning phenomenon of the substance and can emit light of arbitrary color tone ranging from yellowish green to reddish brown. PREPARATION:A calcium compound such as calcium carbonate, an alkaline earth metal compound such as magnesium carbonate, a manganese compound such as manganese carbonate and a Dy, Sm, Lu, Bi, Cu, Eu, Ce or La compound such ad dysprosium oxide are mixed and then calcined for example in an atmosphere of a sulfide gas such as hydrogen sulfide at 1,200 deg.C for 3hr to form the substance of formula.
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