Modeling the Light Extraction Efficiency of Bi-Layer Phosphors in White LEDs

In this letter, we modeled the bi-layer phosphors in light-emitting diode packages and optimized the concentration gradient to enhance the light extraction efficiency (LEE). The modeling processes were presented in detail. Based on our bi-layer model, we changed the concentration from 0.05 to 0.4 ${\rm g/cm}^{3}$ in both the upper and lower phosphor layers. It was found that when the concentration gradient between the upper layer and lower layer increases from 0.05:0.4 to 0.4:0.05, the LEE would be enhanced as much as 17.63%. The trends were validated by experiments. Some potential ways were proposed to realize this kind of phosphor configuration where the concentration of the upper layer was larger than that of the lower layer.