A Remote Phosphor Coating by Lens Wetting for Phosphor-Converted White Light-Emitting Diodes

In our previous study, we demonstrated a remote phosphor coating method by lens wetting for pcLEDs. For the proposed method, the phosphor gel droplet is dropped onto the concave inner surface of a hemispherical lens, then the phosphor gel wets the lens surface driven by gravity and surface tension and finally reaches to a stable geometry. In this study, fluid flow simulations based on Volume of Fluid (VOF) model were applied to investigate the geometry evolution of phosphor gel droplets after been dropped into the lens, and the final geometries with phosphor gel volume range from 4 mu l to 20 mu l were studied. Optical simulations based on Monte Carlo ray tracing method was applied to investigate the optical performance of LED samples with the final geometries obtained from VOF simulations. The VOF simulation results show that when the phosphor volume is less than 10 mu l, the proposed lens wetting method tends to realize uniform thickness phosphor geometry, and when the phosphor volume is more than 10 mu l, the proposed method tends to form the non-uniform thickness phosphor geometry. Optical simulation results show that the vertical LED chip modules with remote phosphor geometry formed by the proposed method have better ACU performance than those with spherical cap phosphor geometry fabricated by the dispensing phosphor coating method. When the average CCT is about 5000 K, a smallest angular CCT deviation of 275 K was achieved when the volume is 17 mu l, while the CCT deviation of the conventional spherical cap phosphor geometry is 2499 K.