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Luminescence characteristics of Ce:Y3Al5O12 (YAG) glass-ceramic (GC) phosphor for a white LED were investigated. The GC phosphor was obtained by a heat treatment of a Ce-doped SiO2-Al2 O3-Y2O3 mother glass between 1300degC and 1500degC for the prescribed time period. The quantum efficiency (QE) of Ce3+ 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 Gd2O3 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 Gd3+ ions in the precipitated YAG microcrystals, leading to the increase of lattice constant of unit cell, which was confirmed by XRD.