Improvement of spatial color uniformity in white light-emitting diodes with self-positioned phosphor layer

To reduce the variance of color temperature among packages and the spatial color temperature variance in the package, we adopted a unique phosphor conformal coating technique in the packaging process, thereby fabricating the self-positioned phosphor layer. Additionally, to acquire the spatial color uniformity without considerable shrinkage of luminous efficacy, we applied sub-micrometer scale titanium dioxide particles as diffuser in the phosphor layer of white LED with a vertical type chip and investigated the effects of diffuser on the spatial color uniformity and optical performance. Regardless of the diffuser content, spatial color uniformity improved and luminous efficacy decreased with the increase of the diffuser content. At the optimum of particle content, spatial color uniformity is reduced by 50% but luminous efficacy decreased only by 3%.