Exellent color quality and luminous flux of wleds using triple-layer remote phosphor configuration

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This study proposed a triple-layer remote phosphor (TRP) structure to improve the color and luminous ux of white LEDs (WLEDs). TRP structure consists of 3 di erent phosphor layers: yellow YAG:Ce3+ layer below, red CaMgSi2O6:Eu2+,Mn2+ phosphor on top and green layer Ba2Li2Si2O7:Sn2+,Mn2+ phosphor in the middle.

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Nội dung Text: Exellent color quality and luminous flux of wleds using triple-layer remote phosphor configuration

VOLUME: 4 | ISSUE: 1 | 2020 | March Exellent Color Quality and Luminous Flux of Wleds Using Triple-Layer Remote Phosphor Configuration 1 1 2,∗ Min-Feng LAI , Hsiao-Yi LEE , Doan Quoc Anh NGUYEN Department of Electrical Engineering, National Kaohsiung University of Science and 1 Technology, Kaohsiung, Taiwan 2 Power System Optimization Research Group, Faculty of Electrical and Electronics Engineering, Ton Duc Thang University, Ho Chi Minh City, Vietnam *Corresponding Author: NGUYEN Doan Quoc Anh (Email: nguyendoanquocanh@tdtu.edu.vn) (Received: 21-Aug-2019; accepted: 12-Dec-2020; published: 31-Mar-2020) DOI: http://dx.doi.org/10.25073/jaec.202041.255 ment in the concentration range of 10% -14% CaMgSi2 O6 :Eu2+ ,Mn2+ , regardless of Abstract. This study proposed a triple-layer Ba2 Li2 Si2 O7 :Sn2+ ,Mn2+ concentration. LE, in remote phosphor (TRP) structure to improve particular, can also increase by more than 40% the color and luminous ux of white LEDs along with the improvement of CRI and CQS (WLEDs). TRP structure consists of 3 dierent due to the reduction of the backscattered light phosphor layers: yellow YAG:Ce3+ layer below, and the addition of green light. Research results red CaMgSi2 O6 :Eu2+ ,Mn2+ phosphor on top are a valuable reference for producers who wish and green layer Ba2 Li2 Si2 O7 :Sn2+ ,Mn2+ to improve the color quality and enhance the phosphor in the middle. Using red luminous ux of WLEDs. CaMgSi2 O6 :Eu2+ ,Mn2+ to control the red light component leads to the increase in color rendering index (CRI). Utilizing the Keywords green CaMgSi2 O6 :Eu2+ ,Mn2+ phosphor to control the green light component results in WLEDs, triple-layer structure, remote the increase in luminous ecacy (LE) of phosphor package, color quality, luminous WLEDs. Furthermore, when the concentra- ux. tion of these two phosphors increased, yellow layer YAG:Ce3+ concentration decreased to maintain average correlated color tempera- tures (ACCTs) in the range from 6000K to 1. Introduction 8500K. Besides CRI and LE, color quality scale (CQS) is also analyzed through the control Phosphor-converted white light-emitting diodes of green and red phosphors concentrations. (WLEDs) with many outstanding features such The research results show that the higher the as smallness, energy saving, cost eciency and concentration of CaMgSi2 O6 :Eu2+ ,Mn2+ is, cohesion in color have been perceived as a new the better the CRI becomes. In contrast, CRI and improved light source [1]-[4]. The comple- decreased signicantly when increasing the mentary principle of colors is applied in WLEDs concentration of Ba2 Li2 Si2 O7 :Sn2+ ,Mn2+ . as blue light from the blue chip and yellow light Meanwhile, CQS achieved notable enhance- from the phosphor layer merge in the congu- 74 c 2020 Journal of Advanced Engineering and Computation (JAEC)
VOLUME: 4 | ISSUE: 1 | 2020 | March ration [5]. It is expected that WLEDs will be The luminous eciency of the device will be low- used for solid-state lighting system; however, the ered as a result, especially at lower CCTs. Thus, luminous eciency must be improved in order the improvements in the blue and yellow light to be used for the aforementioned purpose [6]- emission and the reduction in light loss from [9]. In order to produce the white light, us- backscattering and reection are desirable tar- ing the freely dispersed coating method is the gets. most well-known one. The transparent encapsu- The triple-layer remote phosphor struc- lated resin and the phosphor powder are mixed ture WLEDs with color temperatures from and then dispersed on the phosphor package to 6000K to 8500K are proposed in this study. fabricate the white light in the process. This The TRP structure consists of three dif- procedure may allow better control over phos- ferent phosphor layers with green phos- phor layer thickness and signicantly lower the phor layer Ba Li Si O :Sn ,Mn between expenses; however, it cannot support the pro- yellow phosphor layer YAG:Ce and red 2 2 2 7 2+ 2+ duction of high-quality WLEDs [10]-[12]. There- CaMgSi O :Eu ,Mn phosphor layer. The 3+ fore, a method that helps to distribute the color 2+ 2+ green phosphor layer adds green light compo- 2 6 homogeneously and has angular homogeneity of nents to improve the luminous ux emitted while correlated color temperature (CCT) such as the the red light component is supplemented by red conformal coating method is used as a substitu- phosphor layer to improve color quality. The re- tion [13]. The luminous eciency of the confor- sults show that when there is a balance between mal phosphor structure, however, decreases due 3 colors of yellow, green, and red the color qual- to the backscattering eect this structure has. ity can reach the highest value, and the luminous The idea of separating the chip and the phos- ux of WLEDs is reduced only by an insigni- phor layer in remote phosphor structures are cant amount. presented in previous studies [14]-[16]. The extraction eciency benets from the polymer hemispherical shell lens with an interior phos- phor coating that enhances the light extraction 2. Computational inside of the reection structure. Moreover, the luminous eciency is also improved because simulation the air-gap embedded structure reects the light downward. 2.1. Preparation of phosphor In 2018, Nhan's team used the red-emitting materials α−SrO·3B O :Sm for increasing the optical The rst idea of the study is to use the green 2+ properties of single-remote phosphor. By vary- 2 3 ing α−SrO·3B O :Sm concentration from 2% phosphor Ba Li Si O :Sn ,Mn to enrich the 2+ 2+ green light component in WLEDs and enhance 2+ to 24%, the obtained results proposed that color 2 3 2 2 2 7 uniformity, color rendering index (CRI), color luminous ux. The second idea is to use the quality scale (CQS), and luminous ecacy could red phosphor layer CaMgSi O :Eu ,Mn to 2+ 2+ be improved signicantly [17]. With the tar- boost the red light in WLEDs, leading to an 2 6 get of the improvement of CRI and CQS, in increase in CRI and CQS. The paper also de- 2019, Lee's team has applied the red-emitting tails the chemical composition of these phos- Mg TiO :Mn phosphor in the dual-layer re- phor materials that inuences the optical prop- erties of WLEDs. The chemical composition of 4+ mote geometry [18, 19]. However, the luminous 2 4 ux is a disadvantage in these studies. CaMgSi O :Eu ,Mn are presented in detail 2+ 2+ as in Tab. 1. 2 6 The concentration of phosphor, along with To produce CaMgSi O :Eu ,Mn , a proce- the package structure, is also a critical element dure consisting of 6 steps, from mixing, drying, 2+ 2+ that aects the luminous ux. When the phos- 2 6 phor concentration increases, it will cause the double ring, to washing and then drying again, re-absorption loss in the phosphor layer to rise. is required and must be performed following a strict order to achieve the best result. All of c 2020 Journal of Advanced Engineering and Computation (JAEC) 75
VOLUME: 4 | ISSUE: 1 | 2020 | March Tab. 1: Composition of red-emitting CaMgSi O :Eu ,Mn phosphor. 2 6 2+ 2+ By Mole Mole Ingredient Mole (%) weight (mol) Ions (mol) (g) CaO 45.69 150 2.67 Ca 2.67 2+ MgO 16.95 40 0.99 Mg 0.99 2+ SiO 35.82 126 2.10 Si 2.10 4+ Eu O 0.17 3.5 0.01 O 8.13 2 2− MnCO 1.37 9.2 0.08 Eu 0.02 2 3 2+ NH Cl 5.4 Mn 0.08 3 2+ 4 Tab. 2: Composition of green-emitting Ba Li Si O :Sn ,Mn phosphor. 2 2 2 7 2+ 2+ By Mole Mole Ingredient Mole (%) weight (mol) Ions (mol) (g) BaCO 25.04 185 0.94 Ba 0.94 2+ Li CO 14.82 41 0.55 Li 1.11 3 + SiO 29.34 66 1.10 Si 1.10 2 3 4+ SnO 13.48 6.8 0.50 O 7.62 2 2− MnCO 3.95 1.7 0.15 Sn 0.5 2+ NH Br 13.36 49 0.5 Mn 0.15 3 2+ 4 these steps are critical and based on the step(s) mity. Then dry the mixture in the condition before them. The rst step is mixing the mate- of air to reduce it to powder form. The powder rials by dipping into methanol with a few cubic will be fried with N in capped quartz tubes for 1 centimeters of water. Second, let it dry in a con- hour. After that, turning the product to powder 2 dition of air. After the materials are dried, re and put it through the ring process one more them in the capped quartz tubes and fused with time in open quartz boats under 850 C temper- 0 N at the condition of 1000 C for 1 hour and 0 ature but for about 16 hours (overnight). Once then continue to fry the powdery products in the previous step is done, store the nal powder 2 capped quartz tubes but with CO instead of N product in a well-closed container. in an hour at a temperature of 1150 C. The next 2 0 step is to pick up the product and wash it sev- eral times with water. Finally, leave them to dry and we will have the CaMgSi O :Eu ,Mn . 2 6 2+ 2+ 2.2. Simulation of TRP Similar to CaMgSi O :Eu ,Mn the chemi- 2+ 2+ The simulation of RP-WLEDs with the average cal composition for Ba Li Si O :Sn ,Mn are 2 6 2+ 2+ CCT of 8500K, 7700K, 7000K, 6600K, 5600K, presented in Tab. 2. The steps to material- 2 2 2 7 and the remote phosphor structure are sup- ize Ba Li Si O :Sn ,Mn are demonstrated 2+ 2+ ported by the commercial software LightTools as follows. 2 2 2 7 8.1.0 that based on the Monte Carlo ray-tracing We start by mixing BaCO + Li CO + SiO method. In Fig. 1, there is the 3D stimulated using the dry grinding or milling method. Af- 3 2 3 2 physical model WLEDs used to demonstrate ter the rst step, we continue to re the mixture optical simulations of remote package WLEDs. in open boats under 850 C for an hour while The physical model of WLEDs contains a re- 0 adding in H . We will then proceed with SnO + ector that is 8 mm of the bottom length, 2.07 MnCO + NH Br by soaking them in methanol 2 mm in height and 9.85 mm for the top surface and stirring the mixture until it reaches unifor- 3 4 length. The remote phosphor structure with ex- actly 0.08 mm thickness for each phosphor lm 76 c 2020 Journal of Advanced Engineering and Computation (JAEC)
VOLUME: 4 | ISSUE: 1 | 2020 | March overlays on 9 LED chips with the measurements of 1.14 mm bottom square and 0.15 mm height that are embedded in the gaps on the reector. These blue chips emit a radiant ux of 1.16 W at 455 nm wavelength. Even though the concentra- tion of phosphor particles are constantly chang- ing from 2% to 24%, the control over YAG:Ce 3+ wt keeps the average CCT values remain static (a) (b) in their cases. Furthermore, the spectra values of YAG:Ce including absorption spectrum and 3+ emission spectrum are presented in Fig. 1(e). Meanwhile, the excitation spectrum and emis- sion spectrum of CaMgSi O :Eu ,Mn are 2+ 2+ displayed in Fig. 1(f). 2 6 3. Results and discussion (c) (d) Figure 2 shows the CRI values varying with the concentration of red phosphor and green phos- phor from 2% to 20%. The CRI gradually in- creases with the addition of red phosphor con- centration and reaches the maximum value at 20% concentration. On the other hand, the in- crease in green phosphor does not benet CRI, due to the fact that when the concentration of green phosphor rises from 2% to 20%, CRI con- tinuously decreases regardless of the improve- ment in red phosphor or the changes in aver- age correlated color temperature (ACCT). From (e) the results of Fig. 2, it is clear that the red light component in WLEDs, which comes from the red phosphor layer CaMgSi O :Eu ,Mn , 2+ 2+ needs improvement in order to boost the value 2 6 of CRI. When green phosphor Ba Li Si O :Sn ,Mn concentration in- 2+ 2+ creases, the green light component prevails, 2 2 2 7 and that is a disadvantage for CRI because the energy conversion in red phosphorous layer decreases as the concentration of green phos- (f) phor increases. According to TRP structure, the green phosphor layer is below the red Fig. 1: (a) WLEDs, (b) its parameters, (c) Illustra- phosphor layer, which means the light reaches tion of triple-layer remote phosphor congura- tion, (d) the simulation of WLEDs, (e) the mea- the green phosphor layer rst, before going sured spectra of the yellow-emitting YAG:Ce3+ through the red layer. So, green phosphor phosphor, (f) the measured spectra of the red- Ba Li Si O :Sn ,Mn concentration should 2+ 2+ emitting CaMgSi2 O6 :Eu2+ ,Mn2+ phosphor. be reduced as much as possible, if the target is 2 2 2 7 CRI. CRI is the only factor to evaluate color quality as it has the ability to reect the color c 2020 Journal of Advanced Engineering and Computation (JAEC) 77
VOLUME: 4 | ISSUE: 1 | 2020 | March (a) (a) (b) (b) (c) (c) Fig. 2: CRI of TRP as a function of red Fig. 3: CQS of TRP as a function of red CaMgSi2 O6 :Eu2+ ,Mn2+ phosphor and CaMgSi2 O6 :Eu2+ ,Mn2+ phosphor and green Ba2 Li2 Si2 O7 :Sn2+ ,Mn2+ phosphor: (a) green Ba2 Li2 Si2 O7 :Sn2+ ,Mn2+ phosphor: (a) 6000K; (b) 7000K; (c) 8500K 6000K; (b) 7000K; (c) 8500K 78 c 2020 Journal of Advanced Engineering and Computation (JAEC)
VOLUME: 4 | ISSUE: 1 | 2020 | March nates are two important criteria that CRI does not have access to. However, color quality scale (CQS) can eval- uate the combination of three factor: CRI, the preference of the viewer and the color coordi- nates for white light. Hence, in a compari- son between CRI and CQS, CQS value stands out as a more important and dicult target to achieve. The remaining question is how to im- prove the CQS value of WLEDs? Does it only require the enhancement in the red light com- (a) ponent to improve the CRI? To nd answers to these questions, CQS values are also presented in Fig. 3. In general, CQS increases with red CaMgSi O :Eu ,Mn phosphor. 2 6 2+ 2+ However, unlike the CRI, the CQS experiences a small change when the concentration of the green phosphor layer Ba Li Si O :Sn ,Mn 2+ 2+ varies. From the results shown in Fig. 3, it 2 2 2 7 is possible to conrm that both the green phos- phor and the red phosphor contribute to the im- provement of CQS. The balance between 3 col- ors: yellow, green and red is the key to enhance CQS. When the concentration of red phosphor (b) or green phosphor increases, yellow phosphor concentration decreases to maintain the ACCT. The reduced yellow phosphor concentration causes the yellow light component to decrease, and this has two benets. The rst one is re- ducing the amount of backscattered light to the LED chip so that the luminous ux improves signicantly. Another benet of reducing yel- low phosphor concentration is to lower the yel- low light component and replace the yellow light component with the red and green light com- ponents. Gaining control over CQS is the key to manage these 3 color components. CQS (c) increases gradually when the green phosphor Luminous ux of TRP as a function of red Ba Li Si O :Sn ,Mn concentration moves 2+ 2+ phosphor and green from 2% to 10% and then gradually decreases. Fig. 4: 2 2 2 7 CaMgSi O :Eu ,Mn Ba Li Si O :Sn ,Mn phosphor: (a) 6000K; The highest CQS values are obtained when 2+ 2+ 2 6 2+ 2+ Ba Li Si O :Sn ,Mn is from 10% to 14%. 2 2 2 7 (b) 7000K; (c) 8500K 2+ 2+ When the green phosphor concentration is low 2 2 2 7 (2% to 10%), the yellow light component still dominates, therefore, the light transmission en- more correctly in the human eyes when there is ergy is lost due to backscattering, which leads to CQS not reaching its maximum. When the a lighting eect. However, besides the true color of objects, the green and phosphor concentration is between 10% 14%, the green light component is enough preference of the viewers and the color coordi- c 2020 Journal of Advanced Engineering and Computation (JAEC) 79
VOLUME: 4 | ISSUE: 1 | 2020 | March for CQS to reach the highest level. However, number of layers, single layer or double-layer re- if the concentration of Ba Li Si O :Sn ,Mn 2+ 2+ mote phosphor package. The conversion coe- keep going up, the green light components be- cient for blue light converting to yellow light is 2 2 2 7 come excessive, causing a color imbalance among illustrated as β, and γ is the reection coe- the 3 primary colors green, red and yellow. cient of the yellow light. The intensities of blue Therefore, the increase in green phosphor con- light (PB) and yellow light (PY) are the light in- centration from that point onward will cause the tensities from the blue LED, indicated by PB . CQS to decrease. αB; αY are parameters which indicate the pro- 0 Controlling the color quality of remote phos- portions of blue and yellow lights' energy loss phor structures is more complex than that of during the scattering process in the phosphor conformal phosphor or in-cup phosphor struc- layer. tures. It is even more dicult with WLEDs that The lighting eect of pc-LEDs with the have ACCTs from 7000K - 8500K. Nonetheless, double-layer phosphor structure improved signif- the results showed that with the TRP structure icantly in comparison with a single layer struc- the higher the ACCTs, the greater the CQS. In ture: addition to reducing the amount of backscat- tered light, the TRP structure also supports the (P B + P Y ) − (P B + P Y ) 2 2 >0 1 (5) 1 scattering of light inside WLEDs. This enhance- PB + PY 1 1 ment in scattering is benecial to the mixing By using the Mie-theory [20], the scattering of of light components, resulting in a high-quality phosphor particles was studied, and the scatter- white light. However, does this enhancement in ing cross section C for spherical particles is the scattering process reduces the light trans- also computed. The Lambert-Beer law [21] can sca mission energy? calculate the transmitted light power: The focus of the next part is the mathemati- (6) cal model used to calculate the transmitted blue I = I exp (−µ L) 0 ext light and converted yellow light in the double- I is the incident light power, L is the phos- layer phosphor structure, which is an area that phor layer thickness (mm), and µ is the ex- 0 can generate important changes for the LED ef- tinction coecient which can be expressed as ext ciency. The formulas for transmitted blue light µ = N C , where N is the number density and converted yellow light in single layer remote distribution of particles (mm ). Cext (mm ) ext r ext r −3 2 phosphor package with the phosphor layer thick- is the extinction cross-section of phosphor par- ness of 2h are as follows: ticles. (1) Equation (5) certies that the use of addi- PB = PB × e 1 0 −2αB1 h tional phosphor layers enhances the luminous emission of WLEDs. The increase in luminous (2) emission aects red phosphor and green phos- P Y1 = 1 β1 × P B0 −2αY 1 h (e − e−2αB1 h ) phor concentrations, causing them to rise. To 2 αB1 − αY 1 preserve the ACCTs when the concentrations of The transmitted blue light and converted yellow red phosphor and green phosphor increase, the light for double layer remote phosphor package yellow phosphor concentration decreases. The with the phosphor layer thickness of h are ex- vital point in reducing the yellow phosphor con- pressed as follow: centration is to prevent light loss due to the (3) backscattering characteristic. Furthermore, a PB = PB × e −2αB2 h reduced yellow phosphor concentration makes light transmission energy become stronger, ac- 2 0 cording to Lambert-Beer's Law in Equation P Y2 = 1 β2 × P B0 −2αY 2 h (e (4) − e−2αB2 h ) (6). Therefore, the higher the concentrations 2 αB2 − αY 2 of the phosphor layer Ba Li Si O :Sn ,Mn 2+ 2+ The h is the thickness of each phosphor layer or CaMgSi O :Eu ,Mn are, the more pow- 2 2 2 7 2+ 2+ while the subscripts "1" and "2" indicate the erful the luminous ux emitted. However, this 2 6 80 c 2020 Journal of Advanced Engineering and Computation (JAEC)
VOLUME: 4 | ISSUE: 1 | 2020 | March is unfavorable for CQS as that red or green light red light component in WLEDs can be manipu- components exceed a certain limit as this will lated to improve CRI. Researched results show cause color imbalance, which reduces the ob- that the balance of the three colors yellow, green, tained CQS. and red together with the reduction of backscat- According to results available in Fig. 4, tering from the yellow YAG:Ce will provide 3+ phosphor layer Ba Li Si O :Sn ,Mn allows 2+ 2+ the highest color quality and luminous ux. luminous emission (LE) to rise up to more 2 2 2 7 than 40%, regardless of the phosphor concen- tration CaMgSi O :Eu ,Mn due to the in- 2+ 2+ References crease in green light component and the re- 2 6 duction of backscattering eect. The ob- [1] Tang, Y., Li, Z., Liang, G., Li, Z., Li, J., tained results are important references, paving & Yu, B. (2018). Enhancement of luminous the way for manufacturers to choose the ap- ecacy for LED lamps by introducing poly- propriate level of concentration for these two acrylonitrile electrospinning nanober lm. phosphor types to reach their goals. Specif- Optics express, 26(21), 27716-27725. ically, if the target is to achieve high value in CQS and LE, it is optimal to keep the [2] Cho, H., Joo, C. W., Lee, J., Lee, H., Moon, concentrations of Ba Li Si O :Sn ,Mn from 2+ 2+ J., Lee, J. I., ... & Cho, N. S. (2016). De- 10% to 14%, and CaMgSi O :Eu ,Mn at sign and fabrication of two-stack tandem- 2 2 2 7 2+ 2+ 20%. Moreover, LE also increased slightly type all-phosphorescent white organic light- 2 6 with CaMgSi O :Eu ,Mn concentrations at 2+ 2+ emitting diode for achieving high color ren- 6000K and 7000K ACCTs. At ACCT 8500 K, dering index and luminous ecacy. Optics 2 6 LE is almost unchanged in the range of 2% - 14% express, 24(21), 24161-24168. ACCTs. Then, if the green phosphor concentra- tion reaches 20%, LE decreases slightly. [3] Peng, Y., Wang, S., Li, R., Li, H., Cheng, H., Chen, M., & Liu, S. (2016). Luminous ecacy enhancement of ultraviolet-excited white light-emitting diodes through multi- 4. Conclusions layered phosphor-in-glass. Applied optics, In conclusion, the TRP structure with two 55(18), 4933-4938. phosphor layers Ba Li Si O :Sn ,Mn and 2+ 2+ [4] Tang, Y. R., Zhou, S. M., Yi, X. Z., Lin, CaMgSi O :Eu ,Mn was proposed to im- H., & Zhang, S. (2015). Microstructure op- 2 2 2 7 2+ 2+ prove the CRI, CQS, and LE of WLEDs. As timization of the composite phase ceramic 2 6 a result, not only can TRP structure improve phosphor for white LEDs with excellent the color quality, it also improved LE, which luminous ecacy. Optics letters, 40(23), is a new achievement that has never obtained 5479-5481. before. In order to have those results hap- pened, balancing the yellow, green, and red [5] Siao, C. B., Wang, K. W., Chen, H. S., light in these phosphor layers by controlling Su, Y. S., & Chung, S. R. (2016). Ul- the concentration of Ba Li Si O :Sn ,Mn 2+ 2+ tra high luminous ecacy of white Zn x and CaMgSi O :Eu ,Mn is required. The Cd 1-x S quantum dots-based white light 2 2 2 7 2+ 2+ key for controlling the green light compo- emitting diodes. Optical Materials Express, 2 6 nent in WLEDs, which can benet the lu- 6(3), 749-758. minous ux, is to manage the green phos- phor Ba Li Si O :Sn ,Mn . Furthermore, 2+ 2+ [6] Kim, S. H., Song, Y. H., Jeon, S. R., Jeong, the use of multiple phosphor layers is more fa- T., Kim, J. Y., Ha, J. S., ... & Park, 2 2 2 7 vorable for the luminous ux than using one H. J. (2013). Enhanced luminous ecacy single layer. In the meantime, if the control in phosphor-converted white vertical light- over the concentration of red phosphor layer emitting diodes using low index layer. Op- CaMgSi O :Eu ,Mn is gained, it means the 2 6 2+ 2+ tics express, 21(5), 6353-6359. c 2020 Journal of Advanced Engineering and Computation (JAEC) 81
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VOLUME: 4 | ISSUE: 1 | 2020 | March Electrical Engineering, National Kaohsiung Uni- Doan Quoc Anh NGUYEN was born versity of Science and Technology, Kaohsiung, in Khanh Hoa province, Vietnam. He has Taiwan. His research interest is optical material. been working at the Faculty of Electrical and Electronics Engineering, Ton Duc Thang Hsiao-Yi LEE was born in Hsinchu city, Tai- University. Quoc Anh received his PhD degree wan. He has been working at the Department from National Kaohsiung University of Science of Electrical Engineering, National Kaohsiung and Technology, Taiwan in 2014. His research University of Science and Technology, Kaoh- interest is optoelectronics. siung, Taiwan. His research interest is optics science. "This is an Open Access article distributed under the terms of the Creative Commons Attribution License, 83 which permits unrestricted use, distribution, and reproduction in any medium provided the original work is properly cited (CC BY 4.0)."