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

In this study, small- and large-particle-diameter phosphor powders were mixed 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 μabs, scattering coefficient μsca and extinction coefficient μext 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 % is achieved in the white light emitting diode with hybrid phosphors consisting of 60 wt% powder of 22 μm and 40 wt% powder of 4 μm.