Selection of remote phosphor led packages for improving luminous flux

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In this paper, the rst issue presented and analyzed by several experiments is the in- uence 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.

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Nội dung Text: Selection of remote phosphor led packages for improving luminous flux

VOLUME: 4 | ISSUE: 2 | 2020 | June Selection of Remote Phosphor Led Packages for Improving Luminous Flux 1 1 2,∗ Ming Jui CHEN , Hsiao-Yi LEE , Doan Quoc Anh NGUYEN , 3 4 Thi Phuong Loan NGUYEN , Van Tho LE 1 Department of Electrical Engineering, National Kaohsiung University of Science and Technology, Kaohsiung, Taiwan 2 Power System Optimization Research Group, Faculty of Electrical and Electronics Engineering, Ton Duc Thang University, Ho Chi Minh City, Vietnam 3 Faculty of Fundamental 2, Posts and Telecommunications Institute of Technology, Ho Chi Minh City, Vietnam 4 Institute of Tropical Biology, Vietnam Academy of Science and Technology, Ho Chi Minh City, Vietnam Corresponding Author: Doan Quoc Anh NGUYEN (Email: nguyendoanquocanh@tdtu.edu.vn) (Received: 19-Sep-2019; accepted: 03-Feb-2020; published: 30-Jun-2020) DOI: http://dx.doi.org/10.25073/jaec.202042.259 Abstract. In this paper, the rst issue presented timal structure of WLED in improving luminous and analyzed by several experiments is the in- eciency and color rendering index. uence of the distance between phosphor layers in the dual-layer and triple-layer remote pack- age on luminous ux and color rendering prop- Keywords erty. During the simulation, it was realized that it was possible to create a suitable distance to Multi-chip white LEDs, remote phosphor create higher quality white light-emitting diodes package, luminous ecacy, color render- (WLEDs) by adjusting the distance between the ing index. 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 1. Introduction of experiments, it has been proved that the ef- ciency of the two-layer structure gives optical Due to the quick development in digital illumi- properties higher than the three-layer structure nation market, traditional lighting sources be- related to distance. The highest achievable lu- come completely obsolete, which is the reason men output is 0.6 mm for triple-layer structure why phosphor-converted white light emitting and 0.1 mm for dual-layer structure. Mean- diodes (pc-LEDs) tend to become a promising while, the color rendering index changes insignif- lighting source with many opportunities to com- icantly when the distance increases. The triple- pete with the traditional ones in several appli- layer package is not practical for high-power cations [1-3]. However, available pc-LEDs still white LEDs due to the high cost and low conver- confront some imperfections that need to be im- sion eciency. The dual-layer remote phosphor proved and optimized, such as low conversion package with a 0.1 mm phosphorus gap is the op- eciency and color rendering ability, and poor 118 c 2020 Journal of Advanced Engineering and Computation (JAEC)
VOLUME: 4 | ISSUE: 2 | 2020 | June typically three distinct types of phosphor structure that are ring remote p the hemispherical dome,with and remote phosphor 2+ color uniformity. Currently, the yellow emit- phosphor structure a SrO.3B 2 O3package :Sm employing red a doub ting phosphor of white LED structures is di- LEDs [9-14]. Moreover, phosphor layer above a YAG:Ce another proposition 3+ also demonstrates yellow phos- that an package has the advantage of luminous flux and color stability [15-18]. rectly applied onto the LED chip surface, which phor layer can yield 17% more lumen than the embedded white LED is less than that of the conventional one, and thus causes the thermal degradation of phosphor ma- mixed red and yellow phosphor package [19]. difference in phosphor material arrangement plays a significant role in terial, resulting in the reduction of reliability However, double-layertheseremotephosphor layers in phosphor structure this with structure a SrO.3B 2+ 2O3:Sm red pho of products [4-6]. Narendran with his partners are layerplaced can yieldadjacent 17% moreto each lumen other than at ared the mixed random and yellow phospho demonstrated that more than half the down- this structure distance are placed with the LEDadjacent to each chip, andother theat specied a random distance with converted light is backscattered and reected in- the LED chip with phosphor layers has distance between the LED chip with phosphor not been determined in previous pose the most appropriate distance from LED chip to phosphor layers for side the LED, leading to a reduction of the over- layers has not been determined in previous stud- This article has compared the difference in the effect of distance betw all light output [7]. To limit the rays-trapped ies. That's why this paper has an aim to propose and three-layer structures on optical properties, as shown in Figure 1, star phenomenon inside the LED, a new technology the most ability. appropriate In order to achievedistance from an optimized LEDfor design chip to developing the hig called remote phosphor package is discovered. In phosphor layers withinlayers the LED for the greatest package must haveoptical perfor- The effect e been determined. this structure, the phosphor layer is placed at of blue and yellow rays in LEDs by adjusting the distance between ph mance. a suciently large distance from the LED chip, results pointed out that the LEDs of the two-layer remote phosphor packa This better article than has compared triple-layer one. the dierence in the thereby detecting the backscattered photons and eect of distance between phosphor layers and improving the luminous ecacy. LED chips of two-layer and three-layer struc- II. SIMULATION AND COM Due to the existence of an air gap between the tures on optical properties, as shown in Figure 1, LED and the phosphor layer, the eect of heat starting with The effect luminous of the eciency distance between and color phosphor ren- an layers with LED chip can be reduced during the optical performance, dering ability. ing 3-D ray In simulation detection order to with achieve an optimized LightTools software. A thin phosp which leads to more blue and yellow rays be- far away for design fromdeveloping the LED chip the by a transparent high-eciencymaterialLED, layer. The simulati ing converted and transmitted toward the LED phorright the layers position for two different configuration of phosphor packages layers within on the the optical chara Each blue LED chip has a 1.16 W radiation flux at 455nm emission w surface than the conventional cases and yielding LED package must have been determined. The square base within the cavity of the reflector. 1.8 is a uniform refractive better optical properties. In development, the eect enhancement is due to the improvement light emitted. While the shape of the phosphor particle is spherical and th next generation of remote phosphor congura- in theofuse height 2.07ofnmblue and aand yellow bottom lengthrays in Each of 8 nm. LEDs by package has a conv tion is proposed, in which the dual-layer struc- adjusting the distance layer. The refractive index of between the materialphosphor lay-lens is 1.46 a for the convex ture employs the remote phosphor package to CCTand ers valuethe of simulated LED chip. WLEDThe is 8500 K, the concentration simulation results of phospho enhance the luminous eciency of pc-LEDs [8]. stantly changing pointed out thatto maintain the LEDsthe same CCTtwo-layer of the of white LEDsre- during the s Figure 2, the concentration in the dual-layer package has an upward tr This study indicated that if dual-layer remote mote phosphor package exhibits the ability to value stays the same afterward. Meanwhile, the concentration of the tr phosphor structure uses a thin silicon layer, it lighten and display color better than triple-layer ranging from 0.2 – 0.4 mm and slightly decreases when it continuously will get 5% better lumen output than a con- one. thickness of phosphor layers for two cases of structures are set the same. ventional one at the same CCT. Similarly, sev- eral 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 phos- phor structure that are ring remote phosphor (a) (b) (c) structure, remote phosphor package with the Figure 1. (a) Experimented LED package, (b) Dual-layer phosphor stru hemispherical dome, and remote phosphor pack- Fig. 1: (a) Experimented LED package, (b) Dual-layer age employing a double remote micro-patterned phosphor structure, and (c) Triple-layer phos- phosphor lm into pc-LEDs [9-14]. Moreover, phor structure. another proposition also demonstrates that an air gap layer embedded in a remote phosphorus package has the advantage of luminous ux and color stability [15-18]. Light transmitted back to 2. Simulation and the LED chip of air-gap embedded white LED is computation less than that of the conventional one, and thus, the lumen output was enhanced. In addition, The eect of the distance between phosphor lay- the dierence in phosphor material arrangement ers with an LED chip on the light output of pc- plays a signicant role in improving phospho- LED was examined using 3-D ray detection sim- rus conversion eciency. A double-layer remote ulation with LightTools software. A thin phos- c 2020 Journal of Advanced Engineering and Computation (JAEC) 119
(Title of the paper will be placed here) inct types of phosphor structure that are ring remote phosphor structure, remote phosphor package with VOLUME: 4 | ISSUE: 2 | 2020 | June dome, and remote phosphor package employing a double remote micro-patterned phosphor film into pc- eover, another proposition also demonstrates that an air gap layer embedded in a remote phosphorus vantage of luminous flux and color stability [15-18]. Light transmitted back to the LED chip of air-gap phor layer of remote phosphor package is sepa- For the transmitted blue light and blue light ED is less than that of the conventional one, and thus, the lumen output was enhanced. In addition, the phor materialrated far away arrangement playsfrom the LED a significant role chip by a trans- in improving phosphorusat the boundaries conversion of the efficiency. A rst layer 2+ 3+ te phosphor parent structure material layer. with a SrO.3B The simulation 2O3:Sm red phosphorabout the a YAG:Ce yellow phosphor layer above % more lumeneect than the of mixed red and distance yellow phosphor between package [19]. two phosphor layersHowever,PBthese P B0 e−2αB 1 =phosphor 1h layers in (1) laced adjacent to each other at a random distance with for two dierent conguration packages on the the LED chip, and the specified distance 1 between P B0 phosphor layers has not been determined in previous studies. That’s why thisPpaper Y1 =has an aim to pro-(e−2αY1 h − e−2αB1 h ) (2) optical characteristics of LED is performed by 2 αB 1 − αY1 opriate distance from LED chip to phosphor layers for the greatest optical performance. the 3-D model. Each blue LED chip has a 1.16 compared the difference in the effect of distance between phosphor layers and LED chips of two-layer W radiation uctures on optical properties, ux at 455 as shown nm emission in Figure 1, starting wavelength For the with luminous efficiency and transmitted color rendering blue light and blue light achieve an with a height optimized design of for0.15 nm and developing the a 1.14 nm square high-efficiency LED, theatright the position of phosphor boundaries of the second layer LED packagebase within must have beenthe cavity of determined. Thethe reector. effect 1.8 isisdue enhancement a to the improvement in the use −αB2 h −αB2 h w rays in LEDs by adjusting uniform the distance refractive indexbetween layers and the PLED phosphor particles for phosphor B2 chip. = PB 0 esimulation The e = P B0 e−2αB2 h that the LEDs of the two-layer remote phosphor package exhibits the ability to lighten and display color at all wavelengths of light emitted. While the ayer one. (3) shape of the phosphor particle is spherical and 1 β2 × P B0 −2αY2 h the average diameter is 14.5 nm, the reector P Y2 = (e − e−2αB2 h ) II. SIMULATION AND COMPUTATION has a height of 2.07 nm and a bottom length of 2 αB 2 − αY 2 8 nm. Each package has a convex lens boned on −2αY2 h 1 β2 P B0 e−αB2 h e distance between × e phosphor layers with an LED chip on the light output of pc-LED was examined us- + the top surface of the phosphor layer. The re- 2 αB2 − αY2 on simulation with LightTools software. A thin phosphor layer of remote phosphor package−αY is separated fractive index of the material for the convex lens × (e 2h − e −αB2 h ) LED chip by a transparent material layer. The simulation about the effect of distance between two phos- is 1.46 at the excitation wavelength of 460 nm. o different configuration packages on the optical characteristics of LED is performed by 1 βthe 3-D model. −αB2 h 2 P B0 e ip has a 1.16Since the CCT W radiation flux value at 455nmof simulated WLED is emission wavelength 8500 with = a height of 0.15nm and a 1,14nm (e−2αY2 h − e−2αB2 h ) the cavity ofK, thethe concentration reflector. of phosphor 1.8 is a uniform in both refractive index 2 αB 2 − dual- particles at all wavelengths of for phosphor αY 2 e the shape of the phosphor particle package is sphericalisand the averagechang- diameter is 14.5 nm, the reflector has a (4) layer and tri-layer constantly and a bottoming length to of 8 nm. Eachthe maintain package samehas CCTa convex lens boned of white LEDson the top surface of the phosphor ve index of the material for the convex lens is 1.46 at the excitation wavelength whereofh 460 is the nm. notation Since the of the thickness of each during the simulation process as shown in Fig- ulated WLED is 8500 K, the concentration of phosphor in both dual-layer and layer, while tri-layer the subscript package is con- 1 and 2 are used to ure 2. Also in Figure 2, the concentration in the o maintain the same CCT of white LEDs during the simulation process asdescribe shown in theFigurerst and in 2. Also the second phosphor layer, entration in dual-layer the dual-layerpackage package hashas ananupward upward trend trend withwith the the distanceβfrom 0 to 0.1 mm represents theand this conversion coecient for blue me afterward.distance Meanwhile, fromthe 0concentration to 0.1 mmofand this value the tri-layer stays package rapidly lightincreases in the distance converting to yellow light, γ is reection – 0.4 mm andthe coecient, ρv is the particle density; PB, PY samedecreases slightly afterward.when Meanwhile, it continuouslythe concentra- increases to 0.7 mm. The concentration and the hor layers fortion two cases of structures of the tri-layer arepackage set the same. rapidly increases are the intensities of blue light and yellow light in the distance ranging from 0.2 0.4 mm and respectively. α, β are parameters describing the slightly decreases when it continuously increases fractions of the energy loss of blue and yellow to 0.7 mm. The concentration and the thickness lights. of phosphor layers for two cases of structures are set the same. In addition, the paper demonstrated that the lighting eciency pc-LEDs in the double-layer (b) (c) phosphor structure enhances: a) Experimented LED package, (b) Dual-layer phosphor structure, and (c) Triple-layer phosphor structure. (P B2 + Y P2 ) − (P B1 + P Y1 ) >0 (5) P B1 + P Y1 The simulation result and the theoretical cal- culation verify that the transmitted light in- creases and the backscattering light (by the phosphor layer) degrades in the structure of double-layer package, which improves the light- extraction eciency of white LED. By using the Mie theory [20, 21], the scat- tering of phosphor particles was analyzed. Ad- Fig. 2: The concentration of YAG:Ce3+ phosphor with ditionally, in the following expression by using dierent distances between two phosphor struc- the Mie theory, the scattering 2 cross section Csca tures at the same CCT of white LED. for spherical particles can be calculated. The 120 c 2020 Journal of Advanced Engineering and Computation (JAEC)
VOLUME: 4 | ISSUE: 2 | 2020 | June transmitted light power can be computed by the remains the same when the distance increases by Lambert-Beer law: more than 0.1 mm in two-layer structure and sig- nicantly increases by more than 25% when the I = I0 exp(−µext L) (6) distance is about 0.2-0.4 mm in tri-layer struc- ture. When the distance d varies from 0.1-0.7 In this formula, I0 is the incident light power, mm, the concentration varies slightly. L is the phosphor layer thickness (mm), and Figure 3 shows the inuence of the distance µext is the extinction coecient, which can be between phosphor layers and LED chip of re- expressed as: µext = Nr .Cext . Nr is the num- mote phosphor package on the lumen output. −3 ber density distribution of particles (mm ) The result pointed out that light extraction de- and Cext (mm2 ) is the extinction cross-section of pends on the variation of the distance. For the phosphor particles. dual-layer package, the lumen output enhances signicantly and reaches the highest value in the distance of phosphor layers of 0.5 0.6 mm. In 3. Results and discussion contrast, when the distance increases more than 0.6 mm, the luminous ux tends to decrease. To enhance light eciency and LED color qual- It seems that, as the distance d changes from ity, as well as benet the thermal management of 0.5 to 0.6 mm, the two phosphor layers are fur- remote phosphor, a remote phosphor simulation ther separated and the probability of light rays model was developed. This model allows adjust- trapped in the distance between the two layers ing the phosphor position to nd the optimal of phosphorus will decrease. The reected light distance between the phosphor layers and LED shining directly onto the absorption LED chip chips to build the optical properties of the LED. can be reduced and the light passing through During the simulation, the position of the mid- the phosphorus layers can be increased, thus im- dle phosphorus layers must be adjusted while proving the eciency of the LED. With a dis- the top phosphorus layer should be xed. How- tance of 0.5 - 0.6 mm, heat generated by the ever, the reection, absorption, scattering, con- LED chip only transfers to the substrate instead version, and transmission of light in LED can of the contact surface of two phosphor layers. lead to the variation of the correlated color tem- The distance growth of phosphor layers may not perature of LED according to the location and only improve luminous ux but also create tem- arrangement of the phosphor layers in both dual- perature stability of this multi-layer phosphor layer and tri-layer package. Therefore, the phos- conguration, which results in more light be- phor concentration needs to change with the dis- ing transmitted and extracted through phospho- tance between the phosphor and LED chips, as rus layers. For a range of 0.6 mm to 0.7 mm shown in Figure 2, to be able to preserve the distance, the reduction of luminous ux is at- CCT of this package. tributed to the weak photon extraction and the thermal eect of phosphor. Blue light from LED The phosphor concentration of dual-layer chip will encounter the rst phosphor layer and package tends to decrease in the range 0 - 0.1 convert the blue light to the yellow light. How- mm and does not change afterward. It can be as- ever, part of the light is lost inside the LED due sumed that two phosphor layers placed at a short to backscattering, absorption, and reection, the distance of 0 - 0.1 mm looks like a single phos- rest is turned into yellow light and transmit- phor layer with a double thickness. As known ted through the second phosphorus layer. The in the previous studies, increasing the phosphor increasing distance makes the phosphorus layer layer thickness can enhance the scattering, the move closer to the LED chip, and therefore more absorption, and the reection, thus causing a light is trapped inside the gap between this phos- high color correlation temperature within the phorus layer and the LED chip, as well as the LED package. Therefore, it is necessary to re- back-reected light to the LED chip. This causes duce the phosphor concentration to ensure that an increase in the junction temperature of both this package has the same CCT during the simu- phosphorus and LED chips, which can produce 3+ lation. The YAG:Ce phosphor concentration c 2020 Journal of Advanced Engineering and Computation (JAEC) 121
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 outputVOLUME: enhances 4significantly | ISSUE: 2 |and 2020 | June 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 low conversion eciency. For the three-layer trapped cases of in multi-layer the distance between phosphorus the twoconguration layers of phosphorus is will decrease. T structure, the process of propagating light in- absorption the same,LED chipbe it can canobserved be reduced and the that the light CRIpassing of the through the phospho side the LED has an opposite tendency. The the efficiencyphosphor dual-layer of the LED.conguration With a distanceisofbetter0.5 - 0.6 mm, heat generated by than luminous ux also increases at the beginning of instead of the contact surface of two phosphor that of the tri-layer one as shown in Figure 4. In layers. The distance growth of p nous flux but also create temperature stability of this multi-layer phosphor con the distance of 0 - 0.1 mm and decreases at the conclusion, the change in position, as well as the transmitted and extracted through phosphorus layers. For a range of 0.6 mm to position of 0.1 - 0.7 mm distance. The simu- amount of phosphorus in the remote phosphorus flux is attributed to the weak photon extraction and the thermal effect of phosp lation results show that the case of the double- package, ter the first signicantly phosphor layer aected and convert thetheluminous blue lightux, to the yellow light. How layer package has better improvement than the CRI. due The best luminous to backscattering, absorption,ux andand CRI can reflection, be is turned into yello the rest three-layer package as shown in Figure 3. Pc- achieved at phosphorus theThe layer. optimal distance increasing distanceof makes 0.1 mm the in a phosphorus layer move LEDs with the dual-layer remote phosphor pack- light is trapped two-layer insidephosphorus remote the gap between this phosphorus package. The two- layer and the LED ch age show a rapid increase of the luminous ux LED layerchip. This causes package oersan increase great in the junction advantages temperature of both phospho in bringing which is higher than that of the triple-layer phos- conversion efficiency. For the three-layer high luminous ux and CRI. The blue light and structure, the process of propagatin dency. The luminous flux also increases at the beginning of the distance of 0 - phor package at the beginning. The photons yellow light must pass through three layers of - 0.7 mm distance. The simulation results show that the case of the double-lay are extracted into the total light energy of the phosphorus in the three-layer package, so there three-layer package as shown in Figure 3. Pc-LEDs with the dual-layer remote two-layer conguration including higher content is still the a large luminous possibility flux which is higherthatthan athat rayof of the light is triple-layer phosphor packag than the three-layer conguration. lost ed intoinside these the total light three energy layers of the (Title ofpaper phosphorus. two-layer of the configuration will including higher co be placed here) Figure. 3. The luminous efficiency of white LEDs at the same CCT with different distances between two phosphor structures. Fig. 3: The luminous eciency of white LEDs at the Figure 4. The color rendering index (CRI) value of white LEDs with different distance same CCT with dierent distances between two Fig. 4: The color rendering index (CRI) value of white The phosphorphosphor structures.of dual-layer package tends to decreaseLEDs concentration with in the dierent range 0 - 0.1distance mm andbetween two does not phos- after- change ward. It can be assumed that two phosphor layers placed at a short distance phor layers of 0at -the 0.1same mm CCT. looks like a single phosphor layer Inwithaddition, a double thethickness. eect Asof known in the previous the distance between studies, increasing the phosphor layer thickness can enhance the scattering, the absorption, and the reflection, two layers of phosphorus on the color rendering thus causing a high color correlation temperature within the LED package. Therefore, it is necessary to reduce the phosphor index was studied. For both types of multi-layer concentration to ensure that this package has the same CCT during the simulation. The YAG:Ce3+ phosphor concentration remains the4. same when Conclusion the distance increases by more than 0.1 mm in congurations, when the distance is appropri- two-layer structure and significantly increases by more than 25% when the distance is about 0.2-0.4 mm in tri-layer struc- ate, the probability of the transition intensity ture. When the distance d varies from 0.1-0.7 mm, the concentration varies slightly. and the transmission intensity of blue light and In this study, several experiments were carried Figure 3 shows the influence of the distance between phosphor layers and LED chip of remote phosphor package on the yellow light increase. The heat generated by out in order to analyze and demonstrate the in- lumen output. The result pointed out that light extraction depends on the variation of the distance. For the dual-layer pack- age,LED chips output the lumen often enhances transferssignificantly into the substrate and reaches in-the uence of the highest value indistance the distancebetween phosphor of phosphor layers layers of 0.5 – 0.6 mm. stead of phosphor, In contrast, when thewhich helps distance avoid more increases the chemi- than 0.6 mm,andthe LED chip as luminous fluxwell tendsastothe number decrease. phosphor It seems that, as the cal change distance of phosphor d changes from 0.5 as wellmm, to 0.6 as the the destruction two phosphor layerslayersare onfurther the pc-LED separatedoptical and thecharacteristics probability of lightat rays of LEDs trapped in thedue to heat distance problems. between the twoThislayersprovides a of phosphorus the willsame CCT. decrease. TheThe suitable reflected lightposition of phos- shining directly onto the absorption LED chip spectrum wider emission can be reduced and location at this the light passing of thethrough phor the phosphorus layer in remote layers can be increased, phosphor package thus which improving is thephosphorus efficiency of layer the LED.andWith makesa distance the colorof 0.5 - 0.6 mm, quality of heat generatedvia discovered by several the LEDexperiments chip only transfers to the the can have substrate instead of the contact the LED and the surface CRI of two phosphor better at the samelayers.time. The distance growth luminous uxof and phosphor colorlayers may notindex rendering only improve of LED lumi- nous flux but also create temperature stability of this multi-layer phosphor configuration, When the distance is too large or the rst phos- signicantly bettered. In addition, the luminous which results in more light being transmitted and extracted through phosphorus phorus layer is very close to the LED chip, the layers. For a range of 0.6 mm to 0.7 mm distance, ux remarkably enhances and reaches the max- the reduction of luminous fluxblue is attributed to the weak photon extraction and the thermal effect of phosphor. rays are scattered back and trapped inside imum value at the distance of 0.6 mm for the Blue light from LED chip will encoun- ter the first phosphor layer and convert the blue light to the yellow light. However, part of the light is lost inside the LED the LED package. Consequently, the light qual- case of trial-layer package and 0.1 mm for dual- due to backscattering, absorption, and reflection, the rest is turned into yellow light and transmitted through the second ity becomes worse and hence the color rendering layer package. Meanwhile, with the distance phosphorus layer. The increasing distance makes the phosphorus layer move closer to the LED chip, and therefore more index is low. Although the CRI trend for both ranging from 0.1 mm to 0.7 mm of dual-layer 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 ten- dency. 122 The luminous flux also increases at the beginning of the distance of 0 - 0.1 mm and decreases at the position of 0.1 c 2020 Journal of Advanced Engineering and Computation (JAEC) - 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-
VOLUME: 4 | ISSUE: 2 | 2020 | June package, the lumen output and the color qual- [7] Yu, S. D., Li, Z. T. Liang, G. W. Tang, Y. ity of LEDs have a slight downward tendency. Yu, B. H., & Chen, K. H. (2016). Angu- The increase of the trapping, the absorption, the lar color uniformity enhancement of white re-scattering of light in LED package, and the light-emitting diodes by remote micro- chemical change of the heated phosphor layer patterned phosphor lm. Photonics Re- are the main reason for this issue. Therefore, the search, 4(4), 140-145. key issue of this scientic paper is how to nd [8] Jeon, S. W., Kim, S. H. Choi, J. N. Jang, an appropriate space between phosphor layers in I. S. Song, Y. H. Kim, W. H., & Kim, J. remote phosphor package in designing pc-LEDs P. (2018). Optical design of dental light us- with outstanding eciency. ing a remote phosphor light-emitting diode package for improving illumination unifor- mity. Applied Optics, 57(21), 5998-6003. References [9] Xie, B., Chen, W. Hao, J. N. Wu, D. Yu, X. J. Chen, Y. H. Hu, R. Wang, K., & [1] Anh, N. D. Q., Le, P. X., & Lee, H. Y. Luo, X. B. (2016). Structural optimization (2019). Enhanced luminous ux of white for remote white light-emitting diodes with LED using at dual-layer remote phosphor quantum dots and phosphor: packaging conguration. Journal of Advanced Engi- sequence matters. Optics Express, 24(26), neering and Computation, 3(2), 426-432. A1560-A1570. [2] Li, C. N., Rao, H. B. Zhang, W. [10] Li, J. S., Li, Z. T. Liang, G. W. Yu, S. Zhou, C. Y. Zhang, Q., & Zhang, K. D. Tang, Y., & Ding, X. R. (2016). Color (2016). Self-Adaptive ConformalRemote uniformity enhancement for COB WLEDs Phosphor Coating of Phosphor-Converted using a remote phosphor lm with two White Light Emitting Diodes. Journal of freeform surfaces. Optics Express, 24(21), Display Technology, 12(9), 946-950. 23685-23696. [3] Anh, N. D. Q, Le, P. X., & Lee, H. Y. [11] Shih, B. J., Chiou, S. C. Hsieh, Y. H. Sun, (2019). Selection of a Remote Phosphor C. C. Yang, T. H. Chen, S. Y., & Chung, T. Conguration to Enhance the Color Qual- Y. (2015). Study of temperature distribu- ity of White LEDs. Current Optics and tions in pc-WLEDs with dierent phosphor Photonics, 3(1), 78-85. packages. Optics Express, 23(26), 33861- 33869. [4] Li, Z. T., Wang, H. Y. Yu, B. H. Ding, X. [12] Guo, Z. Q., Lu, H. L. Shih, T. M. Lin, R., & Tang, Y. (2017). High-eciency LED Y. Lu, Y. J., & Chen, Z. (2016). Spectral COB device combined diced V-shaped pat- Optimization of Candle-Like White Light- tern and remote phosphor. Chinese Optics Emitting Diodes With High Color Render- Letters, 15(4). ing Index and Luminous Ecacy. Journal of Display Technology, 12(11), 1393-1397. [5] Ying, S. P., & Shen, J. Y. (2016). Con- centric ring phosphor geometry on the [13] Ma, R., Ma, C. Y., Zhang, J. T., Long, luminous eciency of white-light-emitting J. Q., Wen, Z. C., Yuan, X. Y., & Cao, diodes with excellent color rendering prop- Y. G. (2017). Energy transfer properties erty. Optics Letters, 41(9), 1989-1992. and enhanced color rendering index of chro- maticity tunable green-yellow-red-emitting [6] Chiang, C. H., Tsai, H. Y. Zhan, T. S. Lin, 3+ 3+ Y3 Al5 O12 :Ce ,Cr phosphors for white H. Y. Fang, Y. C., & Chu, S. Y. (2015). light-emitting diodes. Optical Materials Ex- Eects of phosphor distribution and step- press. 7(2), 454-467. index remote conguration on the perfor- mance of white light-emitting diodes. Op- [14] Anh, N. D. Q., Vinh, N. H., & Lee, tics Letters, 40(12), 2830-2833. H. Y. (2017). Eect of Red-emitting c 2020 Journal of Advanced Engineering and Computation (JAEC) 123
VOLUME: 4 | ISSUE: 2 | 2020 | June Sr2.41 F2.59 B20.03 O74.8 :Eu0.12 ,Sm0.048 Phos- [21] Lee, H. Y., Le, P. X., & Anh, N. D. phor on Color Rendering Index and Lumi- Q. (2019). The Impacts of Red-emitting 4+ nous Ecacy of White LEDs. Current Op- Mg2 TiO4 :Mn Phosphor on Color Quality tics and Photonics, 1(2), 118-124. of Dual-layer Remote Phosphor Congura- tion. Journal of Advanced Engineering and Computation, 3(3), 464-470. [15] Li, N. Q., Zhang, Y. Quan, Y. W. Li, L. Ye, S. H. Fan, Q. L., & Huang, W. (2018). High- eciency solution-processed WOLEDs with About Authors very high color rendering index based on a macrospirocyclic oligomer matrix host. Op- Ming Jui CHEN was born in Tainan tical Materials Express, 8(10), 3208-3219. city, Taiwan. He has been working at the Department of Electrical Engineering, National [16] Li, Y. Y., Chen, J. J. Feng, H. H. Chen, Kaohsiung University of Science and Technol- H., & Wang, Q. M. (2014). Rugate lters ogy, Kaohsiung, Taiwan. His research interest used in slit-lamp delivery to improve color is optical material. rendering of illumination for retinal photo- coagulation. Applied Optics, 53(15), 3361- Hsiao-Yi LEE was born in Hsinchu city, Tai- 3369. wan. He has been working at the Department of Electrical Engineering, National Kaohsiung University of Science and Technology, Kaoh- [17] Ou, Y. Y., Corell, D. D., Dam-Hansen, siung, Taiwan. His research interest is optics C. Petersen, P. M., & Ou, H. Y. (2011). science. Antireective sub-wavelength structures for improvement of the extraction eciency Doan Quoc Anh NGUYEN was born and color rendering index of monolithic in Khanh Hoa province, Vietnam. He has white light-emitting diode. Optics Express, been working at the Faculty of Electrical 19(S2), A166-A172. and Electronics Engineering, Ton Duc Thang University. Quoc Anh received his PhD degree from National Kaohsiung University of Science [18] He, G. X., & Tang, J. (2015). Study on the and Technology, Taiwan in 2014. His research correlations between color rendering indices interest is optoelectronics. and the spectral power distributions: com- ment. Optics Express, 23(3), A140-A145. Thi Phuong Loan NGUYEN was born in Da Nang province. In 2006, She received her master degree from University of Natural Sci- [19] Hung, P. C., & Tsao, J. Y. (2013). Max- ences. Her research interest is optoelectronics. imum White Luminous Ecacy of Radi- She has worked at the Faculty of Fundamental ation Versus Color Rendering Index and 2, Posts and Telecommunications Institute of Color Temperature: Exact Results and a Technology, Ho Chi Minh City, Vietnam. Useful Analytic Expression. Journal of Dis- play Technology, 9(6), 405-412. Van Tho LE was born in Thanh Hoa province, Vietnam. In 2019, he received his master degree from the University of Science [20] Huyal, I. O., Ozel, T. Koidemir, U. Vietnam National University. His research Nizamoglu, S. Tuncel, D., & Demir, V, H. interest is optoelectronics. He has worked at (2008). White emitting polyuorene func- Institute of Tropical Biology, Vietnam Academy tionalized with azide hybridized on near- of Science and Technology. UV light emitting diode for high color ren- dering index. Optics Express, 16(2), 1115- 1124. 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)."