Influence of ZrO₂ particles on the optical properties of pc-LEDs

Experimental and modeling progress and results aiming to increase the color uniformity of hemisphere-type pcW-LEDs are proposed. By adding micrometric zirconia particles, the light scattering is enhanced, that induces a decrease of phosphor necessary to obtain a specific CCT. The optical model is able to determine the optical properties (CCT, angular CCT distribution, chromaticity and packaging efficiency) in a hemisphere LED for various amount of YAG-phosphor and ZrO₂-zirconia particles. Based on previous process, the work is in the first step to fit the effective radius and refractive index that will be implemented in the optical model. In the second step, the optical model is compared with the experimental measurement to determine the absorption coefficient and conversion efficiency of a package of silicone resin containing phosphor and zirconia. Finally, the model, confirmed by selected experimental results, allows determining the optical properties of any king of package that lead to a CCT emission ranging from 4500 K to 6500 K. The analysis of these data is interpreted by comparing, for a specific CCT, the phosphor loss, the packaging efficiency and the angular distribution of CCT. The results show that if the effort is targeted on one of the previous parameters, there is always a counterpart on the other ones. Increasing the color uniformity will induce to decrease the packaging efficiency.