Optimization of the Yellow Phosphor Concentration and Layer Thickness for Down-Conversion of Blue to White Light

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 mu m thick 25 mm X 25 mm film prepared from 30 mg of phosphor in 500 mu l of the PMMA-chlorobenzene solution.