Enhancing color quality of WLEDs with dual-layer remote phosphor geometry

Usually, remote phosphor structures are beneficial in terms of flux but unfavorable in terms of color quality compared to conformal phosphor or in-cup phosphor packages. To eliminate this disadvantage, many studies have focused on increasing the chromatic quality of the remote phosphor configuration, which requires great efforts in improving two parameters of color: color rendering index (CRI) and color quality scale (CQS). CRI is known as the most useful quantitative method used to measure the ability of a light source to reproduce the colors of illuminated objects faithfully and naturally. Similarly, CQS is also a method of lighting quality determination and analysis, especially used as an alternative to the unsaturated CRI colors. In this paper, we proposed dual-layer remote phosphor structure as a novel method of CRI and CQS enhancement to improve WLEDs’ color quality. Five alike WLEDs but having different color temperatures in the range of 5600 K to 8500 K were applied in this study. The idea behind the study is to place a red phosphor layer Sr_wF_xB_yO_z:Eu²⁺,Sm²⁺ on the yellow phosphor layer YAG:Ce³⁺ and then determining an appropriate concentration of Sr_wF_xB_yO_z:Eu²⁺,Sm²⁺ added to achieve the highest color quality. The results point out that Sr_wF_xB_yO_z:Eu²⁺,Sm²⁺ brings great benefits to the improvement of CRI and CQS parameters. Specifically, the higher the Sr_wF_xB_yO_z:Eu²⁺,Sm²⁺ concentration results in the greater CRI and CQS, owning to the enriched red light components in the WLEDs. However, the flux has a tendency of dropping when Sr_wF_xB_yO_z:Eu²⁺,Sm²⁺ concentration rises excessively. This has been proved by using the Mie-scattering theory and the Lambert-Beer law. The results of this article are essential references for manufacturing WLEDs with higher chromatic quality.