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Comparison between SEPs of CaCO3 and TiO2 in phosphor layer for better color uniformity and stable luminous flux of WLEDs with 7,000 K

100%

Le P. X. , Trang T. T. , Anh N. D. Q. , Lee H.-Y. , Tho L. V.

Materials Science Poland

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2022

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tom Vol. 40, No. 1

1--8

EN

CaCO3 and TiO2 are proposed in this study as particles for scattering enhancement (SEPs) of phosphor-converted white light-emitting diodes (pc-WLEDs). The use of these two SEPs for scattering improvement enables boosting of the color homogeneity of the WLED devices. Each SEP is mixed with YAG:Ce3+ and silicone composition to examine their optical influences and performances on the high-power WLED packages with 7,000 K color temperature (CT). Miescattering theory is applied to calculate and investigate the scattering elements - scattering coefficients, anisotropic scattering, the reduced scattering, and scattering amplitudes - at the wavelengths of 450 nm and 550 nm. The results exhibit that TiO2and CaCO3 considerably promote higher color uniformity and color-deviated reduction, respectively. The obtained results could be primarily attributed to the significant improvement in the scattering properties of the structure. Additionally, the effects of the presented scattering enhancement on luminous efficiency are displayed. The reduction in lumen output is observed to have a close connection with the concentration and particle size of TiO2and CaCO3, which means that control must be exercised over these factors when utilizing these SEPs for WLED fabrication.

2

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

86%

That P. T. , Loan N. T. P. , Tho L. V. , Anh N. D. Q. , Liao H.-Y. , Luo G.-F. , Lee H.-Y.

Materials Science Poland

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2020

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tom Vol. 38, No. 4

667--674

EN

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.

3

The impacts of Ba2Li2Si2O7:Sn2+,Mn2+ and CaMgSi2O6:Eu2+,Mn2+ particles on the optical properties of remote phosphor LED

72%

Chen M.-J. , Loan N. T. P. , Tho L. V. , Bui T. M. , Le P. X. , Anh N. D. Q. , Liao H.-Y. , Chang J.-C. , Lee H.-Y.

Materials Science Poland

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2020

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tom Vol. 38, No. 1

197--205

EN

As implied in the title, the triple-layer remote phosphor (TRP), constructed with the yellow YAG:Ce3+ layer at the bottom, the red CaMgSi2O6:Eu2+,Mn2+ phosphor layer on the top, and the green Ba2Li2Si2O7:Sn2+,Mn2+ phosphor layer between these two layers, is suggested in this paper to improve the color and luminescence of white LEDs (WLEDs). In order to control the red light for the purpose of increasing the color rendering index (CRI), it is suggested that the red CaMgSi2O6:Eu2+,Mn2+ phosphor should be applied in the TRP structure. Simultaneously, the structure uses the green Ba2Li2Si2O7:Sn2+,Mn2+ phosphor layer to control the green light, which increases the luminous efficacy (LE) of WLEDs. In addition, when the concentration of these two phosphors increases, the yellow YAG: Ce3+ concentration must be reduced to keep the average correlated color temperatures (ACCTs) stable at 6000 K to 8500 K. Besides, appropriate adjusting of CRI, LE, and color quality scale (CQS) is also analyzed by modifying the concentration of the green phosphor and red phosphor. The results show that the CRI can get better values if CaMgSi2O6:Eu2+,Mn2+ concentration is higher. In contrast, the CRI decreases dramatically when the concentration of Ba2Li2Si2O7:Sn2+,Mn2+ increases. Meanwhile, CQS can be significantly increased in the range of 10 % to 14 % CaMgSi2O6:Eu2+,Mn2+, regardless of the concentration of Ba2Li2Si2O7:Sn2+,Mn2+. In particular, along with the improvement of CRI and CQS, LE can also be increased by more than 40 % by reducing the scattered light and adding the green light. Obtained results are a valuable reference for manufacturers for improving WLEDs color and luminescence quality to produce a broader range of WLEDs with better quality fulfilling social needs.