Selection of Remote Phosphor Led Packages for Improving Luminous Flux

In this paper, the rst issue presented and analyzed by several experiments is the inuence of the distance between phosphor layers in the dual-layer and triple-layer remote package on luminous ux and color rendering property. During the simulation, it was realized that it was possible to create a suitable distance to create higher quality white light-emitting diodes (WLEDs) by adjusting the distance between the phosphor layers. According to the study results, 0.1 mm is the most reasonable distance between two phosphor layers so that the performance of the multi-chip white light LED (MCW LED) can get the best optimal e ect. Through a series of experiments, it has been proved that the efciency of the two-layer structure gives optical properties higher than the three-layer structure related to distance. The highest achievable lumen output is 0.6 mm for triple-layer structure and 0.1 mm for dual-layer structure. Meanwhile, the color rendering index changes insignificantly when the distance increases. The triplelayer package is not practical for high-power white LEDs due to the high cost and low conversion e ciency. The dual-layer remote phosphor package with a 0.1 mm phosphorus gap is the optimal structure of WLED in improving luminous e ciency and color rendering index.

and analyzed by several experiments is the inuence of the distance between phosphor layers in the dual-layer and triple-layer remote package on luminous ux and color rendering property. During the simulation, it was realized that it was possible to create a suitable distance to create higher quality white light-emitting diodes (WLEDs) by adjusting the distance between the phosphor layers. According to the study results, 0.1 mm is the most reasonable distance between two phosphor layers so that the performance of the multi-chip white light LED (MCW LED) can get the best optimal eect. Through a series of experiments, it has been proved that the efciency of the two-layer structure gives optical properties higher than the three-layer structure related to distance. The highest achievable lumen output is 0.6 mm for triple-layer structure and 0.1 mm for dual-layer structure. Meanwhile, the color rendering index changes insignificantly when the distance increases. The triplelayer package is not practical for high-power white LEDs due to the high cost and low conversion eciency. The dual-layer remote phosphor package with a 0.1 mm phosphorus gap is the op-

Introduction
Due to the quick development in digital illumination market, traditional lighting sources become completely obsolete, which is the reason why phosphor-converted white light emitting diodes (pc-LEDs) tend to become a promising lighting source with many opportunities to compete with the traditional ones in several applications [1][2][3]. However, available pc-LEDs still confront some imperfections that need to be improved and optimized, such as low conversion eciency and color rendering ability, and poor 118 c 2020 Journal of Advanced Engineering and Computation (JAEC) VOLUME: 4 | ISSUE: 2 | 2020 | June color uniformity. Currently, the yellow emitting phosphor of white LED structures is directly applied onto the LED chip surface, which causes the thermal degradation of phosphor material, resulting in the reduction of reliability of products [4][5][6]. Narendran with his partners demonstrated that more than half the downconverted light is backscattered and reected inside the LED, leading to a reduction of the overall light output [7]. To limit the rays-trapped phenomenon inside the LED, a new technology called remote phosphor package is discovered. In this structure, the phosphor layer is placed at a suciently large distance from the LED chip, thereby detecting the backscattered photons and improving the luminous ecacy.
Due to the existence of an air gap between the LED and the phosphor layer, the eect of heat can be reduced during the optical performance, which leads to more blue and yellow rays being converted and transmitted toward the LED surface than the conventional cases and yielding better optical properties. In development, the next generation of remote phosphor conguration is proposed, in which the dual-layer structure employs the remote phosphor package to enhance the luminous eciency of pc-LEDs [8].
This study indicated that if dual-layer remote phosphor structure uses a thin silicon layer, it will get 5% better lumen output than a conventional one at the same CCT. Similarly, several methods were included in the study in order to lessen the power of the light backward from the phosphor layer to the absorptive LED chip.
There are typically three distinct types of phosphor structure that are ring remote phosphor structure, remote phosphor package with the hemispherical dome, and remote phosphor package employing a double remote micro-patterned phosphor lm into pc-LEDs [9][10][11][12][13][14]. Moreover, another proposition also demonstrates that an air gap layer embedded in a remote phosphorus package has the advantage of luminous ux and color stability [15][16][17][18] [19].
However, these phosphor layers in this structure are placed adjacent to each other at a random distance with the LED chip, and the specied distance between the LED chip with phosphor layers has not been determined in previous studies. That's why this paper has an aim to propose the most appropriate distance from LED chip to phosphor layers for the greatest optical performance.
This article has compared the dierence in the eect of distance between phosphor layers and LED chips of two-layer and three-layer structures on optical properties, as shown in Figure  typically three distinct types of phosphor structure that are ring remote p the hemispherical dome, and remote phosphor package employing a doub LEDs [9][10][11][12][13][14]. Moreover, another proposition also demonstrates that an package has the advantage of luminous flux and color stability [15][16][17][18]. embedded white LED is less than that of the conventional one, and thus difference in phosphor material arrangement plays a significant role in double-layer remote phosphor structure with a SrO.3B 2 O 3 :Sm 2+ red pho layer can yield 17% more lumen than the mixed red and yellow phospho this structure are placed adjacent to each other at a random distance with the LED chip with phosphor layers has not been determined in previous pose the most appropriate distance from LED chip to phosphor layers for This article has compared the difference in the effect of distance betw and three-layer structures on optical properties, as shown in Figure 1, star ability. In order to achieve an optimized design for developing the hig layers within the LED package must have been determined. The effect e of blue and yellow rays in LEDs by adjusting the distance between ph results pointed out that the LEDs of the two-layer remote phosphor packa better than triple-layer one.

II. SIMULATION AND COM
The effect of the distance between phosphor layers with an LED chip ing 3-D ray detection simulation with LightTools software. A thin phosp far away from the LED chip by a transparent material layer. The simulati phor layers for two different configuration packages on the optical chara Each blue LED chip has a 1.16 W radiation flux at 455nm emission w square base within the cavity of the reflector. 1.8 is a uniform refractive light emitted. While the shape of the phosphor particle is spherical and th height of 2.07 nm and a bottom length of 8 nm. Each package has a conv layer. The refractive index of the material for the convex lens is 1.46 a CCT value of simulated WLED is 8500 K, the concentration of phospho stantly changing to maintain the same CCT of white LEDs during the s Figure 2, the concentration in the dual-layer package has an upward tr value stays the same afterward. Meanwhile, the concentration of the tr ranging from 0.2 -0.4 mm and slightly decreases when it continuously thickness of phosphor layers for two cases of structures are set the same.  (Title of the paper will be placed here) 2 nct types of phosphor structure that are ring remote phosphor structure, remote phosphor package with ome, and remote phosphor package employing a double remote micro-patterned phosphor film into pcover, another proposition also demonstrates that an air gap layer embedded in a remote phosphorus antage of luminous flux and color stability [15][16][17][18]. Light transmitted back to the LED chip of air-gap D is less than that of the conventional one, and thus, the lumen output was enhanced. In addition, the hor material arrangement plays a significant role in improving phosphorus conversion efficiency. A e phosphor structure with a SrO.3B 2 O 3 :Sm 2+ red phosphor layer above a YAG:Ce 3+ yellow phosphor more lumen than the mixed red and yellow phosphor package [19]. However, these phosphor layers in aced adjacent to each other at a random distance with the LED chip, and the specified distance between phosphor layers has not been determined in previous studies. That's why this paper has an aim to propriate distance from LED chip to phosphor layers for the greatest optical performance. ompared the difference in the effect of distance between phosphor layers and LED chips of two-layer ctures on optical properties, as shown in Figure 1, starting with luminous efficiency and color rendering achieve an optimized design for developing the high-efficiency LED, the right position of phosphor ED package must have been determined. The effect enhancement is due to the improvement in the use rays in LEDs by adjusting the distance between phosphor layers and the LED chip. The simulation hat the LEDs of the two-layer remote phosphor package exhibits the ability to lighten and display color yer one.

II. SIMULATION AND COMPUTATION
distance between phosphor layers with an LED chip on the light output of pc-LED was examined usn simulation with LightTools software. A thin phosphor layer of remote phosphor package is separated ED chip by a transparent material layer. The simulation about the effect of distance between two phosdifferent configuration packages on the optical characteristics of LED is performed by the 3-D model. p has a 1.16 W radiation flux at 455nm emission wavelength with a height of 0.15nm and a 1,14nm the cavity of the reflector. 1.8 is a uniform refractive index for phosphor particles at all wavelengths of the shape of the phosphor particle is spherical and the average diameter is 14.5 nm, the reflector has a nd a bottom length of 8 nm. Each package has a convex lens boned on the top surface of the phosphor e index of the material for the convex lens is 1.46 at the excitation wavelength of 460 nm. Since the lated WLED is 8500 K, the concentration of phosphor in both dual-layer and tri-layer package is conmaintain the same CCT of white LEDs during the simulation process as shown in Figure 2. Also in ntration in the dual-layer package has an upward trend with the distance from 0 to 0.1 mm and this e afterward. Meanwhile, the concentration of the tri-layer package rapidly increases in the distance 0.4 mm and slightly decreases when it continuously increases to 0.7 mm. The concentration and the or layers for two cases of structures are set the same.
) Experimented LED package, (b) Dual-layer phosphor structure, and (c) Triple-layer phosphor structure. (1) For the transmitted blue light and blue light at the boundaries of the second layer In addition, the paper demonstrated that the lighting eciency pc-LEDs in the double-layer phosphor structure enhances: In this formula, I 0 is the incident light power, L is the phosphor layer thickness (mm), and µ ext is the extinction coecient, which can be expressed as: µ ext = N r .C ext . N r is the number density distribution of particles (mm −3 ) and C ext (mm 2 ) is the extinction cross-section of phosphor particles.

Results and discussion
To  (Title of the paper will be placed here) Figure. 3. The luminous efficiency of white LEDs at the same CCT with different distances between two phosphor structures.
The phosphor concentration of dual-layer package tends to decrease in the range 0 -0.1 mm and does not change afterward. It can be assumed that two phosphor layers placed at a short distance of 0 -0.1 mm looks like a single phosphor layer with a double thickness. As known in the previous studies, increasing the phosphor layer thickness can enhance the scattering, the absorption, and the reflection, thus causing a high color correlation temperature within the LED package. Therefore, it is necessary to reduce the phosphor concentration to ensure that this package has the same CCT during the simulation. The YAG:Ce 3+ phosphor concentration remains the same when the distance increases by more than 0.1 mm in two-layer structure and significantly increases by more than 25% when the distance is about 0.2-0.4 mm in tri-layer structure. When the distance d varies from 0.1-0.7 mm, the concentration varies slightly. Figure 3 shows the influence of the distance between phosphor layers and LED chip of remote phosphor package on the lumen output. The result pointed out that light extraction depends on the variation of the distance. For the dual-layer package, the lumen output enhances significantly and reaches the highest value in the distance of phosphor layers of 0.5 -0.6 mm. In contrast, when the distance increases more than 0.6 mm, the luminous flux tends to decrease. It seems that, as the distance d changes from 0.5 to 0.6 mm, the two phosphor layers are further separated and the probability of light rays trapped in the distance between the two layers of phosphorus will decrease. The reflected light shining directly onto the absorption LED chip can be reduced and the light passing through the phosphorus layers can be increased, thus improving the efficiency of the LED. With a distance of 0.5 -0.6 mm, heat generated by the LED chip only transfers to the substrate instead of the contact surface of two phosphor layers. The distance growth of phosphor layers may not only improve luminous flux but also create temperature stability of this multi-layer phosphor configuration, which results in more light being transmitted and extracted through phosphorus layers. For a range of 0.6 mm to 0.7 mm distance, the reduction of luminous flux is attributed to the weak photon extraction and the thermal effect of phosphor. Blue light from LED chip will encounter the first phosphor layer and convert the blue light to the yellow light. However, part of the light is lost inside the LED due to backscattering, absorption, and reflection, the rest is turned into yellow light and transmitted through the second phosphorus layer. The increasing distance makes the phosphorus layer move closer to the LED chip, and therefore more light is trapped inside the gap between this phosphorus layer and the LED chip, as well as the back-reflected light to the LED chip. This causes an increase in the junction temperature of both phosphorus and LED chips, which can produce low conversion efficiency. For the three-layer structure, the process of propagating light inside the LED has an opposite tendency. The luminous flux also increases at the beginning of the distance of 0 -0.1 mm and decreases at the position of 0.1 -0.7 mm distance. The simulation results show that the case of the double-layer package has better improvement than the three-layer package as shown in Figure 3. Pc-LEDs with the dual-layer remote phosphor package show a rapid increase of the luminous flux which is higher than that of the triple-layer phosphor package at the beginning. The photons are extract- two-layer structure and significantly increases by more than 25% when the dis ture. When the distance d varies from 0.1-0.7 mm, the concentration varies slig Figure 3 shows the influence of the distance between phosphor layers and L lumen output. The result pointed out that light extraction depends on the variat age, the lumen output enhances significantly and reaches the highest value in mm. In contrast, when the distance increases more than 0.6 mm, the luminous distance d changes from 0.5 to 0.6 mm, the two phosphor layers are further trapped in the distance between the two layers of phosphorus will decrease. T absorption LED chip can be reduced and the light passing through the phospho the efficiency of the LED. With a distance of 0.5 -0.6 mm, heat generated by instead of the contact surface of two phosphor layers. The distance growth of p nous flux but also create temperature stability of this multi-layer phosphor con transmitted and extracted through phosphorus layers. For a range of 0.6 mm to flux is attributed to the weak photon extraction and the thermal effect of phosp ter the first phosphor layer and convert the blue light to the yellow light. How due to backscattering, absorption, and reflection, the rest is turned into yello phosphorus layer. The increasing distance makes the phosphorus layer move light is trapped inside the gap between this phosphorus layer and the LED ch LED chip. This causes an increase in the junction temperature of both phospho conversion efficiency. For the three-layer structure, the process of propagatin dency. The luminous flux also increases at the beginning of the distance of 0 --0.7 mm distance. The simulation results show that the case of the double-lay three-layer package as shown in Figure 3. Pc-LEDs with the dual-layer remote the luminous flux which is higher than that of the triple-layer phosphor packag ed into the total light energy of the two-layer configuration including higher co   124 "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)."