The application of dual-layer remote phosphor geometry in achieving higher color quality of WLEDs

Abstract

If remote phosphor structures are put into comparison with conformal phosphor or in-cup phosphor, their luminous flux are better, but the color quality is not as elevated. This leads to an obvious need of a practical solution to enhance color quality. Therefore, many studies were carried out to achieve this purpose, and so is ours. We proposed using two layers of phosphor in WLEDs to achieve better rendering ability and chromatic performance. The identical WLEDs with different color temperatures, 5600 K-8500 K, were used and reported in this paper. Our research consists of two parts, which are placing a layer of red phosphor Sr_wF_xB_yO_z:Eu²⁺,Sm²⁺on the yellow YAG:Ce³⁺ phosphor layer at first, and then specifying an appropriate Sr_wF_xB_yO_z:Eu²⁺,Sm²⁺ concentration to reach the highest color performance. It is shown that with the contribution of Sr_wF_xB_yO_z:Eu²⁺,Sm²⁺,the color rendering index (CRI) and color quality scale (CQS) are increased. This can be explained by the increased amount of red light components in the WLEDs when the concentration of Sr_wF_xB_yO_z:Eu²⁺,Sm²⁺ was greater. However, excessive Sr_wF_xB_yO_z:Eu²⁺,Sm²⁺ will cause the reduction in the flux, which has been proven by the application of Mie scattering and the Lambert-Beer law. Therefore, the conclusion will present an optimal amount of Sr_wF_xB_yO_z:Eu²⁺,Sm²⁺ to obtain high color quality while minimizing the light loss.