Color Uniformity Enhancement of White Light-Emitting Diodes With Novel Bell Shape Phosphor Layer

In this study, we proposed a bell shape phosphor layer geometry and the corresponding dual-step phosphor coating method for enhancing the angular color uniformity (ACU) of phosphor-converted white light-emitting diodes (pcLEDs). Numerical simulation based on Volume of Fluid (VOF) model was applied to predict phosphor geometries. Based on the simulated results, experiments were conducted to realize the phosphor geometries. The simulated results show that the VOF model can predict the phosphor geometries with an acceptable geometric deviation within 5%. The experimental results show that compared with the spherical cap phosphor layer geometry, the bell shape geometry can achieve better ACU performance, an optimal bell phosphor layer geometry with equal coating volume above and around the LED chip was achieved, for the corrected color temperature (CCT) of 4000 K, the angular CCT deviation of the optimal geometry is 62 K, while it is 382 K for the spherical cap geometry.