Patent ID: 7291290

Claim:
A europium-activated phosphor, comprising; a divalent europium ratio of a particle of the phosphor is lower at and in a vicinity of a particle surface than for the particle as a whole and an average europium concentration of the particle of the phosphor is higher at and in the vicinity of a particle surface than for the particle as a whole, wherein the europium-activated alkaline earth metal aluminate phosphor whose composition is Ba 1-x Sr y Eu z MgAl 10 O 17 , where 0.05≦x≦0.40, 0≦y≦0.25, 0.05≦z≦0.30, and x−y≦z for the particle as a whole, and 3z≦z′≦10z at and in the vicinity of the particle surface, z′ being a europium concentration, and to divalent europium ratio is a ratio of divalent europium to a sum total of trivalent europium and the divalent europium in a predetermined part of the particle.