Luminescence characteristics of Ce:Y ₃ Al ₅ O ₁₂ (YAG) glass-ceramic (GC) phosphor for a white LED were investigated. The GC phosphor was obtained by a heat treatment of a Ce-doped SiO ₂ -Al ₂ O ₃ -Y ₂ O ₃ mother glass between 1300degC and 1500degC for the prescribed time period. The quantum efficiency (QE) of Ce ³⁺ fluorescence in the GC materials, the color coordinate, and the luminous flux of electroluminescence of LED composite were evaluated with a blue LED (465 nm) set in an integrating sphere. The QE increased with increasing ceramming temperature of the as-made glass. The color coordinates ( x , y ) of the composite were increased with increasing thickness of the GC mounted on a blue LED chip. The effect of Gd ₂ O ₃ substitution on the optical properties of the GC materials was also investigated. The excitation and emission wavelengths shifted to longer side up to Gd/(Y + Gd) = 0.40 in molar composition. As a result, the color coordinate of the LED with GdYAG-GC of various thickness shifted to closer to the Planckian locus for the blackbody radiation. These results were explained by partial substitution of Gd ³⁺ ions in the precipitated YAG microcrystals, leading to the increase of lattice constant of unit cell, which was confirmed by XRD.

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