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2 Materials Science Poland

2 2020

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

That Phung Ton, Loan Nguyen Thi Phuong, Tho Le Van, Anh Nguyen Doan Quoc, Liao Hsing-Yuan, Luo Guo-Feng, Lee Hsiao-Yi

Materials Science Poland

2020

Vol. 38, No. 4

667--674

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 SrwFxByOz:Eu2+,Sm2+ on the yellow phosphor layer YAG:Ce3+ and then determining an appropriate concentration of SrwFxByOz:Eu2+,Sm2+ added to achieve the highest color quality. The results point out that SrwFxByOz:Eu2+,Sm2+ brings great benefits to the improvement of CRI and CQS parameters. Specifically, the higher the SrwFxByOz: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 SrwFxByOz: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.

Enhancement of color quality and luminous flux for remote-phosphor LEDs with red-emitting CaMgSi2O6:Eu2+,Mn2+

Luo Guo-Feng, Loan Nguyen Thi Phuong, Tho Van Le, Anh Nguyen Doan Quoc, Lee Hsiao-Yi

Materials Science Poland

2020

Vol. 38, No. 3

409--415

SiO2 particles and red-emitting CaMgSi2O6:Eu2+,Mn2+ phosphor have been added into a yellow phosphor compound YAG:Ce3+ to enhance the optical efficiency of white light LEDs whose average correlated color temperature (CCT) is in the range of 5600 K ÷ 8500 K. It was observed that altering CaMgSi2O6:Eu2+,Mn2+ concentration from 2 % to 30 % while maintaining 5 % of the SiO2 strongly influenced the color rendering index (CRI), color quality scale (CQS), and lumen efficiency of the compound. Besides, through the application of Monte Carlo simulation and Mie-scattering theory, it was possible to improve the optical properties by CaMgSi2O6:Eu2+,Mn2+ and SiO2 addition. The results provided a practical approach to achieve higher luminous efficiency and better color uniformity in remote-phosphor white LEDs (RP-WLEDs).