Enhance WLEDs Performance with Additional Phosphor Materials in Multi-Layer Remote Structure

One of the most important factors used to evaluate lighting performances of WLEDs is the angular color uniformity (ACU). The triple-layer remote phosphor structure is considered as a proposed mechanism for elevating the ACU of a WLED. The analysis on the triple-layer structure's e ciency is speci cally demonstrated in this article. Additionally, there are detailed comparisons between the triple-layer (TL) and the dual-layer (DL) geometries to reinforce the idea of using TL packaging for WLED optical enhancements. The WLEDs with average correlated color temperatures (ACCTs) of 6600 K and 7700 K are utilized for experiments. According to the outcomes, the attained color rendering index from DL design is higher than the one from TL package. However, the TL shows better color quality scale (CQS) than the DL, regardless of ACCTs. Besides, not only does the TL yield better CQS but also heighten the lumen e ciency. On top of that, the ACU of TL WLED model is much higher than that of the DL as a result of deviated correlated color temperature reduction at all ACCTs. This result is more obvious at the high ACCT of 7700 K, in other words, the ACU of a high-ACCT WLED shows more visible enhancement with TL structure. From these results, the triple-layer remote phosphor structure stands out as the promising advancement in the production of high-quality


Introduction
With outstanding features, including small size, energy eciency, eco friendliness, and longevity, which have gained much recognition in the lighting industry, white light-emitting diodes (WLEDs) have spread out in illuminating applications. Lighting design, street lighting, household lighting, and headlamps are the aspects that WLEDs are frequently utilized [1]- [3]. In general, the popular method for phosphor-converted WLED production is intec 2021 Journal of Advanced Engineering and Computation (JAEC) 167 VOLUME: 5 | ISSUE: 3 | 2021 | September grating blue LED chips with organic resin/yellow Y 3 Al 5 O 12 :Ce 3+ (YAG:Ce 3+ ) phosphor composition [4,5]. Despite its popularity, the organic encapsulation is an obstacle for the development of high-power WLED devices. As the organic silicone encapsulant is inferior in temperature stability and photonic terms, it easily decays and becomes yellowish. As a result, there are degradations in lumen eciency (LE) and long-term reliability, together with the occurrence of color shift in WLED devices after a long service time [6,7]. Besides that, the organic resin has a lower refractive index (RI) which is approximately 1.5, compared to the RI value of the yellow phosphor YAG:Ce 3+ (about 1.83). This dierence in RIs causes the lights to be reected and nally absorbed in a large portion, which means the amount of light that can escape the package is reduced [8,9].
A phosphor-in-glass (PiG) structure, fabricated by sintering glass powders and phosphor grains at a temperature under 800 0 C, was proposed to settle the problems of organic silicone encapsulation. The reason making PiG a better choice for WLED manufacture is their impressive characteristics, which includes the high durability and temperature stability, and low coecient of thermal expansion [10]- [12]. In order to suggest a potential phosphor structure for YAG:Ce 3+ PiG to achieve better performances, the triple-layer remote phosphor conguration is introduced in this research paper.

Simulation process
The illustrations in Fig. 1 show the congurations of dual-layer ( Fig.  1(a)), and triplelayer ( Fig. 1(b)) remote phosphor used in this study. In the dual-layer model, the red phosphor layer is above the yellow phosphor YAG:Ce Meanwhile, for the TL conguration, each phosphor lm has a thickness of 2h 3 and computations of its transmitted blue light and converted yellow light can be demonstrated as: (4) is the parameter indicating the yellow light transmitted through two phosphor lms.
The lighting performance of a WLED device is signicantly enhanced with the application of the triple-layer remote phosphor structure, which is even higher than the light output of the dual-layer model: The scattering properties of phosphor layers are studied through Mie-scattering theory [21], by which the computation of scattering cross section C sca for spherical particles is carried out.
The Lambert-Beer law is also utilized for the calculation of light power: In Eq. (7), the incident light power is indicated by I 0 , while L (mm) expresses the thickness of the phosphor lm. The extinction coecient µ ext is calculated through the following equation: µ ext = N r C ext , with the parameters of N r (mm −3 ) and C ext (mm 2 ) are the number density distribution and the extinction cross-section of phosphor particles, respectively. As the Eq.
(6) implied, the lumen eciency of applying the triple-layer remote phosphor structure is higher than that of using the dual-layer package. In Moreover, the remote phosphor packaging contributes signicantly to backscattering reduction in WLEDs, and as a result the lumen output is better. However, to elevate the power transmission to the highest, the phosphor concentrations must be adjusted properly, according to Eq. (7) that based on the Beer's law. Figure 7 is the demonstration of the correlated color temperature deviation (D-CCT) from the remote phosphor congurations. Obviously, the TL structure is more benecial to the color uniformity than the DL structures.
The D-CCT of the TL is greatly reduced especially at high ACCT WLEDs above 7700 K. 176 "This is an Open Access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium provided the original work is properly cited (CC BY 4.0)."