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When compared with two conformal phosphor and in-cup phosphor structures, the remote phosphor structure has higher luminescent performance. However, it is difficult to control the color quality of the remote phosphor structure, so it has become a research target in recent years. So far, there are two remote phosphor structures used to improve color quality including dual-layer phosphor configuration and triple-layer phosphor configuration. This study suggests using those two configurations to make multi-chip white LEDs (WLEDs) that can achieve adequate values in color rendering index (CRI), color quality scale (CQS), luminous efficacy (LE) and color uniformity. WLEDs with a color temperature of 5600 K are applied. Research results show that the triple-layer phosphor configuration is superior in CRI, CQS, LE. Besides, the color deviation decreases significantly, meaning that the color homogeneity increases with the triple-layer phosphor configuration. This can be demonstrated by analyzing the scattering characteristics of phosphor classes through Mie theory, thus making the research results more reliable and valuable for producing quality WLEDs. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium provided the original work is properly cited.

This paper focuses on the comparison of the luminous flux of two dual-remote phosphor structures named flat dual-remote phosphor (FDRP) and concave dual-remote phosphor (CDRP). These two configurations have different luminous flux values due to the disparity in scattering properties in white LEDs. However, the researched results showed that FDRP structure is more lucrative than the CDRP structure when it comes to the luminous flux effectiveness. To support the aforementioned idea, this article also presents the influence of the distance between two phosphor layers (d1) and the distance between the phosphor layer with the LED surface (d2) on the optical properties of the FDRP structure. Specifically, the scattering ability and absorption properties of the remote phosphor layer will vary sharply if d1 and d2 are adjusted into different values, which produces an immense impact on the chromatic homogeneity and illumination capability of WLEDs. Therefore, in order to stabilize the correlated color temperature (CCT) of WLEDs at 8500 K when there is a modification on d1 and d2, the concentration of YAG: Ce 3+ phosphor also needs to be varied. Accordingly, the scattering process and absorption phenomenon in the remote phosphor layer will bottom out when d1=d2=0, leading to the worst color quality and luminous flux. The effect of the spectra generated as these distances are adjusted is obvious evidence for this point. In other words, the larger the d1 and d2, the larger the scattering surface, and thus the blending of blue and yellow light rays will become more homogeneous, yielding the smallest white light deflection and the lowest luminous flux at the same time. The paper's results indicated that the luminous flux will reach a peak at 1020 lm if d1=0.08 mm or d2=0.63 mm and the chromatic deflection will hit the lowest point as d1=0.64 mm or d2=1.35 mm. In the end, manufacturers can make their choice for the production of higher-standard WLEDs based on the general knowledge and helpful information that the article has provided and analyzed.

In order to clarify the main purpose of the study, we put a green phosphor layer SrBaSiO4:Eu2+ on the yellow phosphorus layer YAG:Ce3+ through using only one WLEDs structure in different color temperatures like 5600 K, 6600 K, 7700 K. Then, we find the suitable SrBaSiO4:Eu 2+ concentration in order that the luminous flux could get the highest value. The results show that SrBaSiO4:Eu 2+ brings great benefits to increase not only optical gain but also color uniformity. Specifically, the greater the SrBaSiO4:Eu 2+ concentration, the greater the output of WLEDs because of the development of green light component in WLEDs. However, only if the SrBaSiO4:Eu 2+ concentration exceeds the level, a slight decrease in color rendering index (CRI) can occur, which based on Monte Carlo simulation. In addition, the results of this paper have contributed significantly to the creation of higher-powered WLEDs.

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