A cerium-doped gadolinium-yttrium garnet yellow emitting phosphor was used to optimize the phosphor layer for down-conversion of blue light from InGaN inorganic light-emitting diode (iLED) to white. Optical, morphological and elemental characterizations of phosphor were carried out. Various amounts of the phosphor were dispersed in polymethyl methacrylate polymer (PMMA)—chlorobenzene solution. The phosphor layer thickness was optimized by varying the volume of the phosphor—PMMA mixture. Using a blue emitting (458 nm) iLED, a two times larger luminance efficacy (lm/W) was obtained from down-converted white light using a 37.5 <i>µ</i>m thick 25 x 25 mm film prepared from 30 mg of phosphor in 500 <i>µ</i>l of the PMMA-chlorobenzene solution.
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