Optimization of light efficacy and angular color uniformity by hybrid phosphor particle size for white light-emitting diode

For phosphor involved wLED, it is reported that phosphor with a larger-particle-diameter brings a relatively higher light efficacy, whereas phosphor with a smaller-particle-diameter provides a better angular color spatial uniformity. This study mixed small- and large-particle-diameter phosphor powders together (hybrid phosphors) to balance light efficacy and angular color uniformity and pursue optimal results. Phosphor with small-particle-diameter of 4 μm was employed and it was mixed into each large-particle-diameter phosphor of 10, 16, 22, and 26 μm, at mass percentage from 0 % to 50 % with an interval of 10 %, respectively. Remote phosphor package was adopted and overall phosphor concentration was kept constant for better comparison. Moreover, absorption coefficient μ_abs, scattering coefficient μ_sca and extinction coefficient μ_ext of each hybrid phosphors were calculated based on Mie theory to further discuss the experiment results. Results show that, the introduction of small-particle-diameter phosphor to large one can highly improve angular color uniformity while only slightly reduce light efficacy. The optimal performance with angular color uniformity of 91.6% as well as normalized light efficacy of 95.7% was achieved in the wLED with hybrid phosphors consisting of 60 wt. % powder of 22 μm and 40 wt. %powder of 4 μm.