Patent ID: 8125139

Claim:
A powdery phosphor comprising particles of an α-sialon represented by the following formula: (M1) x (M2) y (Si) 12−(m+n) (A1) m+n (O) n (N) 16−n , wherein M1 is at least one element selected from the group consisting of Li, Mg, Ca, Y and lanthanide metals (except for La and Ce), M2 is at least one element selected from the group consisting of Ce, Pr, Eu, Tb, Yb and Er, 0.3≦X+Y≦1.5, 0<Y≦0.7, 0.6≦m≦3.0, 0≦n≦1.5, X+Y=m/2, an actual oxygen content in the powdery phosphor comprising particles of the α-sialon is larger than a theoretical value calculated based on the formula in an amount of less than 0.4 wt. % of said theoretical value, and a transparent material having a refractive index of from 1.2 to 2.5 and a thickness of from 5 nm to 100 nm is coated on at least a part of a surface of the particles of the α-sialon.