Microsoft Word 00 a loinoidau(moi thang12 2016)(tienganh) docx 16 Anh Q D Nguyen, Vinh H Nguyen EFFECTS OF RED Y2O3 EU3+ PHOSPHOR IN SILICONE LENS ON THE COLOR RENDERING ABILITY OF WHITE LED LAMPS Anh[.]
16 Anh Q D Nguyen, Vinh H Nguyen EFFECTS OF RED Y2O3:EU3+ PHOSPHOR IN SILICONE LENS ON THE COLOR RENDERING ABILITY OF WHITE LED LAMPS Anh Q D Nguyen, Vinh H Nguyen Nguyen Tat Thanh University, Ho Chi Minh city, Vietnam anhkuas@gmail.com, nguyenhuuvinh3110@gmail.com Abstract - In this study, a novel compound is synthesized by adding the red Y2O3:Eu3+ dopant to formal phosphor packages, and used as a component in multi-chip white LED lamps (MCW-LEDs) It was found that this solution can enhance the color rendering index (CRI) of MCW-LEDs that have correlated color temperature (CCT) of 8500 K to the value of more than 86 Besides, the impacts of the Y2O3:Eu3+ phosphor on the attenuation of light through phosphor layers with the concentration and sizes of Y2O3:Eu3+ is also demonstrated by the Beer-Lambert law The obtained results indicate that the CRI increases Y2O3:Eu3+ concentration The larger amount Y2O3:Eu3+ powder is used, the higher lumen output is obtained These results provide important information for selecting the optimal combination of phosphor materials in MCW-LEDs for manufacturing Key words - Light-emitting diode; Red Y2O3:Eu3+ Phosphor; color rendering index; Beer-Lambert law; Mie-scattering theory Introduction In recent times, now, LEDs are considered promising products in the future owing to their superior properties for lighting technology, such as high illumination, high energy efficiency, and long lifetimes [1] Therefore, MCW-LEDs which are extensively applied in a variety of generalpurpose illumination applications have replaced traditional light sources Generally, the luminous output and the correlated color temperature uniformity are regarded as the most important factors that determine the quality of LED performance When suitable concentration of SiO2 particles is added to phosphor layer, angular CCT distribution can be optimized without considerably affecting luminous output [2] In addition, the lumen output of MCW-LEDs increases significantly with the Ce0.67 Tb0.33 MgAl11O19:Ce,Tb concentration added to MCW-LEDs phosphor [3] With the aim of improving the CRI of MCW-LED to value greater than 90, several former approaches have been introduced to reimburse the red-light of MCW-LEDs such as combining red-phosphors with phosphor layer or injecting red LEDs [4, 5] Won group combined blue LEDs, green (Ba,Sr)2SiO4:Eu2+ and red CaAlSiN3:Eu2+ phosphors with various packages to proposed great CRI value MCW LEDs [6] Chen group have executed experiments of adding the missing red part in the phosphor converted white lightemitting diodes (pc-WLEDs) [7] Nevertheless, these studies merely examine individual pc-WLED structures Furthermore, the researches simply concentrate on singlechip white LED lamps having CCT varying from 2500 K to 7500 K, but it does not really improve the color rendering ability of MCW-LED lamps and lamps with higher CCTs have not been deeply researched Europium-doped yttrium oxide (Y2O3:Eu3+) phosphor has been applied extensively in lighting technology to contribute red light [8] Due to the great properties as excellent luminescence efficiency, color purity and stability, red phosphor (Y2O3:Eu3+) have met all the requirements for a favorable red-emitting phosphor [9] However, Y2O3:Eu3+ has not been widely applied to enhance CRI yet In this paper, we review the influence of Y2O3:Eu3+ particles in CRI of MCW LEDs in conformal phosphor packages The pc-WLEDs red-light emitting can be controlled by the presence of Y2O3:Eu3+ phosphor particles As a result, the LED light distribution can be adjusted by LED packages to higher CRI region Our study progress is divided into three main steps First, the precise MCW-LED physical model with average CCT approximately 8500 K is built by Light Tools 8.1.0 program Then, Y2O3:Eu3+ particles are mixed into the phosphor layers These particles which interact with transmitted light result in the latter weakened Lastly, we examine the impacts of Y2O3:Eu3+ phosphor concentration on MCW-LEDs CCT The simulation results demonstrate that the proposed approach can increase the CRI substantially In previous studies, the optimal size ranking from µm to µm can be applied for manufacturing MCW-LEDs having high lumen [11, 12] The larger size of phosphor powder is used, the higher luminous flux is accomplished Besides, to enhance CRI, the smaller size (< µm) should be used [12] Correspondingly, the Y2O3:Eu3+ size region from µm to µm have been applied in this paper Experiment and Simulation PC-WLED models built with Light Tools software are covered by a flat silicone These MCW-LED model are set up based on the products information of Siliconware Precision Industries Co., Ltd., Taiwan [10] PC-WLEDs building and phosphor size adjustment are main works in this study The formal phosphor package (CPP) PCWLEDs structures is constructed with average CCT values of 8500 K as presented in Figure 1(a) (a) (b) Figure An actual 8500 K MCW-LED with CPP (a) and its illustration with the red Y2O3:Eu3+ phosphor particles (b) As displayed in Figure 1(b), the reflector has a bottom ISSN 1859-1531 - THE UNIVERSITY OF DANANG, JOURNAL OF SCIENCE AND TECHNOLOGY, NO 12(109).2016 length of mm, a height of 2.07 mm and a length of 9.85 mm at its top surface The conformal phosphor structure, whose thickness is fixed at 0.08 mm, covers nine chips Each LED chip with the square base area of 1.14 mm2 and the height of 0.15 mm is attached to the cavity of the reflector The radiant flux of each blue chip is 1.16 W, and the light emitting wavelength is 453 nm The nine LEDs are formally coated by phosphor layer of CPP The YAG:Ce, Y2O3:Eu3+ particles and the silicone matrix phosphor layers, whose refractive indexes are chosen to be 1.83, 1.93, and 1.50, respectively are key components of phosphor layer The radii of phosphor particles are the same as real particle size, 7.25 µm In order to authenticate the CRI property enhancement of MCW-LED by using Y2O3:Eu3+ phosphor, we fix the average CCT of 8500 K and vary the size of phosphor particles as well as the percentages of Y2O3:Eu3+ Results and Discussion Firstly, the emission spectra of the conformal phosphor compounding are verified with various Y2O3:Eu3+ size and 8% wt Y2O3:Eu3+ Figure indicates that red-lightspectrum-region can be enhanced significantly with small Y2O3:Eu3+ size Indeed, the smaller Y2O3:Eu3+ size is added, the higher red-light-spectrum-region is obtained, resulting in higher CRI The peak wavelengths of the blue chips, the yellow YAG:Ce phosphor and the red Y2O3:Eu3+ phosphor are in turn 453 nm, 555 nm and 680 nm The red Y2O3:Eu3+ phosphor absorb blue light from LED chip for emitting red light The red light spectrum grows with the concentration of Y2O3:Eu3+ phosphor added To maintain the average CCT of 8500K, YAG:Ce wt should be reduced with the addition of Y2O3:Eu3+ in pc-WLEDs The total weigh percentage of pc-WLEDs can be expressed as ∑ W pl = Wyellow phosphor + Wsilicone + Wred phosphor = 100% where the Wsilicone , Wyellow phosphor and Wred phosphor (1) are the weight percentage of the silicone glue, the yellow YAG: Ce phosphor and the red Y2O3:Eu3+ phosphor, respectively 17 Figure The color rendering index at average CCTs of 8500 K with various Y2O3:Eu3+ parameters and with CPP geometry Yellow light (555 nm) is mixed with blue light (453 nm) and red light (680 nm) for emitting white The scattering ability of small size particles is better than that of large size particles, resulting in better absorption ability to blue-light [2] Therefore, the smaller particles are employed, the higher the emission peaks are presented Nevertheless, this can cause a reduction in the transmitted blue-light and the absorption ability of YAG:Ce phosphor Therefore, the emission spectra of 680nm increase while those of 453nm and 555nm decrease The light scattering effect caused by Y2O3: Eu3+ is determined by using Mie-scattering theory [11, 12] with the support of MATLAB as a computation tool Recall that the scattering coefficient μsca(λ) can be calculated with the following equations: (2) , where: - N(r) is the number of Y2O3:Eu3+ particles (per cubic millimeter) - Csca is the scattering cross sections (in square millimeter) Figure Scattering coefficients of Y2O3:Eu3+ in proportion to wavelengths of 453nm, 555nm and 680nm Figure Emission spectra of multiple phosphors with various Y2O3:Eu3+ sizes Next, Figure illustrates the impact of concentration and size of Y2O3:Eu3+ on CRI It can be observed that the CRI grows in accordance with the weight percentage of Y2O3:Eu3+ phosphor in a continuous range from 0% to 16 % 18 Anh Q D Nguyen, Vinh H Nguyen 3+ The higher Y2O3:Eu wt involved, the higher CRI obtained This cause is the enhancement of scattering and absorption ability for Y2O3:Eu3+, see Figure That is also likely for the smaller Y2O3:Eu3+ particles It means that the smaller the size of Y2O3:Eu3+ particles is applied, the higher the CRI is accomplished Indeed, the color rendering index achieved exceeds 86 at 16% wt and 1µm Nevertheless, the transmission ability of blue-light from chips has a less tendency with the higher wt and the smaller size, causing the decrease of lumen output Thus, Y2O3:Eu3+ particle affects a change in both CRI and lumen output, significantly The obtained results in Figure also indicate that the CRI has a decreasing tendency in correlation with the increase of the concentration and size of Y2O3:Eu3+ beyond a point where the red-light starts to be over-dominant, causing color rendering ability to be reduced A proper control of Y2O3:Eu3+ wt and size is very necessary for pc-WLEDs, according to requirements of manufacturing Figure The lumen output and the calculated extinction coefficient of CPP As presented in Figure 5, the lumen output increases with the size of Y2O3:Eu3+ because of the decline of extinction coefficient values The light deterioration is measured by the Beer – Lambert law: I = I0exp(-µextL) (3) Where I is the transmitted light power, I0 is the incident light power, µext = N.Cext is the extinction coefficient, L is the path length and N is the number of particles per cubic millimeter According to Mie-scattering theory, the extinction cross section Cext of phosphor particles can be described by the latter equation: C ext = 2π a x2 ∞ ∑ (2 n + 1) Re( a n + bn ) (4) Here, x = 2πa/λ is the size parameter; an and bn are the expansion coefficients with even symmetry and odd symmetry, respectively The parameters an and bn are defined as: n =1 an ( x, m) = ψ n' (mx)ψ n ( x) − mψ n (mx)ψ n' ( x) ψ n' (mx)ξ n ( x) − mψ n (mx)ξ n' ( x) (5) bn ( x, m) = mψ n' (mx )ψ n ( x ) −ψ n (mx)ψ n' ( x) mψ n' (mx )ξ n ( x ) −ψ n (mx)ξ n' ( x ) (6) Where a which is the spherical particle radius, is the relative scattering wavelength, m is the refractive index of scattering particles, and are the Riccati - Bessel functions Two distinct wavelengths, 555 nm and 453 nm are used to determine the extinction coefficient of the red Y2O3:Eu3+ These wavelengths are chosen because they are corresponding to the emission peaks of the YAG:Ce phosphor and the LED chips, respectively The alteration of these parameters related to the Y2O3:Eu3+ particle sizes as reported by the above equations are performed in Figure It is shown that at the lower Y2O3:Eu3+ particle size is, the lower the lumen output is, which correlates to the higher extinction coefficient values These results can be applied to evaluate the impact of Y2O3:Eu3+ both concentration and size on the lumen output generated by the pc-WLEDs Conclusion This paper has demonstrated the influence of Y2O3:Eu3+ particle size on the CRI as well as the lumen output of MCW-LEDs The simulation results had proved that the CRI value can be enhanced by choosing Y2O3:Eu3+ particle size at small size regime Higher CRI can be achieved while by reducing the size of Y2O3:Eu3+ phosphor applied The highest CRI value is greater than 86 However, the lumen output begin to decrease at small size regime as a result of the increase of extinction coefficient On the contrary, it is obvious that the lumen output can be improved by adding Y2O3:Eu3+ with large size regime The paper demonstrates that Y2O3:Eu3+ phosphor application is an auspicious measure for improving the pc-WLEDs, and consequently, for MCW-LEDs production Acknowledgements This research is funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 103.03-2015.62 REFERENCES [1] N D Q Anh, M F Lai, H Y Ma, H Y Lee, “Enhancing of correlated color temperature uniformity for multi-chip white-light LEDs by adding SiO2 to phosphor layer”, J Chin Inst Eng 38(3), Taylor & Francis, 2015, (297-303) [2] M F Lai, N D Q Anh, H Y Ma, H Y Lee, “Scattering effect of SiO2 particles on correlated color temperature uniformity of multichip white light LEDs”, J Chin Inst Eng 39(4), Taylor & Francis, 2016, (1-5) [3] M F Lai, N D Q Anh, H Y Ma, H Y Lee, “Effects of Ce0.67 Tb0.33 MgAl11 O19:Ce,Tb phosphor on optical performance of multi-chip white LEDs”, Proceedings of Optics & Photonics of Taiwan International Conference, OPTIC, 2014 [4] L Lohaus, E Leicht, S Dietrich, R Wunderlich and S Heinen, “Advanced color control for multicolor LED illumination systems with parametric optimization”, In Proceedings of International Conference on Industrial Electronics Society, IEEE, 2013, (3305- 3310) [5] M Zheng, W Ding, F Yun, D Y Xia, Y P Huang, Y K Zhao, W H Zhang, M Y Zhang, M F Guo and Y Zhang, “Study of High CRI White Light-emitting Diode Devices with Multichromatic Phosphor”, In Proceedings of International Conference on Electronic Components & Technology, IEEE, 2014, (2236-2240) [6] Y H Won, H S Jang, K W Cho, Y S Song, D Y Jeon and H K Kwon, “Effect of phosphor geometry on the luminous efficiency ISSN 1859-1531 - THE UNIVERSITY OF DANANG, JOURNAL OF SCIENCE AND TECHNOLOGY, NO 12(109).2016 of high-power white light-emitting diodes with excellent color rendering property”, Opt Lett 34, 2009, (1-3) [7] K J Chen, C C Lin, H V Han, C Y Lee, S H Chien, K Y Wang, S H Chiu, Z Y Tu, J R Li, T M Chen, X Li, M H Shi and H C Kuo, “Wide-Range Correlated Color Temperature Light Generation From Resonant Cavity Hybrid Quantum Dot Light-Emitting Diodes”, IEEE J Sel Top Quantum Electron, 21(4), IEEE, 2015 [8] V V Bakhmetyev, M M Sychov, L A Lebedev, A B.Vlasenko, S P Bogdanov, E P Sheshin, H Kominami, “Synthesis and characterization of finely dispersed Y2O3:Eu cathodoluminescent phosphors”, In Proceedings of International Conference on Vacuum Electron Sources Conference, IEEE, 2014, (1-2) 19 [9] M Zhang, X H Li, Z X Wang, Q Y Hu, H J Guo, “Synthesis of Y2O3:Eu3+ phosphors by surface diffusion and their photoluminescence properties”, Trans Nonferrous Met Soc China, 20, ScienceDirect, 2010, (115-118) [10] Siliconware Precision Industries Co., Ltd., http://www.spil.com.tw [11] Shuai Y., N T Tran, J P You, F G Shi, “Phosphor size dependence of lumen efficiency and spatial CCT uniformity for typical white LED emitters”, In Proceedings of International Conference on Electronic Components and Technology Conference, IEEE, 2012, (2025-2028) [12] S Liu and X B Luo, LED Packaging for Lighting Applications: Design, Manufacturing and Testing, John Wiley & Sons, 2011 (The Board of Editors received the paper on 08/06/2016, its review was completed on 15/9/2016) ... Figure indicates that red-lightspectrum-region can be enhanced significantly with small Y2O3:Eu3+ size Indeed, the smaller Y2O3:Eu3+ size is added, the higher red-light-spectrum-region is obtained,... beyond a point where the red-light starts to be over-dominant, causing color rendering ability to be reduced A proper control of Y2O3:Eu3+ wt and size is very necessary for pc-WLEDs, according to requirements... (NAFOSTED) under grant number 103.0 3-2 015.62 REFERENCES [1] N D Q Anh, M F Lai, H Y Ma, H Y Lee, “Enhancing of correlated color temperature uniformity for multi-chip white-light LEDs by adding SiO2 to