A plasma display device includes a blue phosphor composed of a compound
represented by Me.sub.3MgSi.sub.2O.sub.8:Eu (where, Me is at least
calcium (Ca), strontium (Sr), or barium (Ba)). Concentration of bivalent
Eu ions is 45 to 95% and concentration of trivalent Eu ions is 5 to 55%,
of the europium (Eu) atoms contained in the blue phosphor layer. The
plasma display device has less luminance degradation in a panel
manufacturing process, high luminance, and long lifetime.