Light extraction efficiency enhancement of white LEDs by bi-layer phosphor configuration

Experimental investigations were carried out on the light extraction efficiency (LEE) of the phosphor-converted white light-emitting diodes (LEDs) with bi-layer phosphor configuration. Phosphor modeling process was briefly introduced. It is found that when the upper phosphor's concentration is 0.4 g/cm3 and the lower layer's concentration is 0.05 g/cm3, the LEE was enhanced as much as 23.0%. It was concluded that when upper phosphor layer has larger concentration than the lower layer, the LEE would be enhanced. The mechanisms behind the phenomena were discussed.