Optoelectronics and Advanced Materials, Rapid Communications
Though remote phosphor structure is not an optimal solution for color quality of WLEDs, it is more beneficial to the LED’s lumen output than the conformal coating or in-cup phosphor structures. Acknowledging the ability of remote phosphor structure, many researches have been conducted to surmount the disadvantage of this structure in color quality. In this research article, a dual-layer remote phosphor structure with the improvement of color rendering index (CRI) and color quality ratio (CQS) of the WLED is reported. The WLED packages used in this study have the color temperature of 8500 K. The configuration of the phosphor structure will be built by placing a layer of green Y2O3:Ho3+ or red LaAsO4:Eu3+ phosphor on the yellow YAG:Ce3+ phosphor layer. Then, the concentration of added phosphor LaAsO4:Eu3+ will be adjusted to get the highest chromatic homogeneity. The experimental results demonstrated the rise in CRI and CQS values with the added LaAsO4:Eu3+, which means the presence of LaAsO4:Eu3+ has a great effect on these two aspects. Specifically, due to the growth of red light components inside WLEDs packages, the more the concentration of LaAsO4:Eu3+ is added, the better the CRI and CQS become. Meanwhile, with green phosphor Y2O3:Ho3+, the luminous flux is benefited. Nevertheless, when the concentrations of both red LaAsO4:Eu3+ and green Y2O3:Ho3+ phosphors surpass the corresponding level, the luminescent efficiency and color quality are reduced. This result is demonstrated based on the Mie-scattering theory and Lambert-Beer's law. The findings in this research are important references for manufacturing WLED packages with improved white-light quality.
