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.