Digest Journal of Nanomaterials and Biostructures Vol. 13, No. 2, April - June 2018, p

Transcription

1 Digest Joural of Naomaterials ad Biostructures Vol. 13, No. 2, April - Jue 2018, p EFFECT OF THE GREEN-EMITTING CaF 2 :Ce 3+,Tb 3+ PHOSPHOR PARTICLES SIZE ON COLOR RENDERING INDEX AND COLOR QUALITY SCALE OF THE IN-CUP PACKAGING MULTICHIP WHITE LEDs N. H. K. NHAN a, T. H. Q. MINH a*, T. N. NGUYEN b, M. VOZNAK b, V. V. HUYNH c a Optoelectroics Research Group, Faculty of Electrical ad Electroics Egieerig, To Duc Thag Uiversity, Ho Chi Mih City, Vietam b VSB-Techical Uiversity of Ostrava, 17. listopadu 15/2172, Ostrava - Poruba, Czech Republic c Faculty of Electrical ad Electroics Egieerig, To Duc Thag Uiversity, Ho Chi Mih City, Vietam I this paper, we ivestigate the effect of the gree-emittig CaF 2 :Ce 3+, Tb 3+ phosphor particle s size o the color rederig idex (CRI) ad the color quality le (CQS) of the i-cup packagig multichip white LEDs (MCW-LEDs). For this purpose, 7000K ad 8500K i-cup packagig MCW-LEDs is simulated by the commercial software Light Tools. Moreover, tterig process i the phosphor layers is ivestigated by usig Mie Theory with Mat Lab software. Fially, the research results show that the gree-emittig CaF2:Ce 3+,Tb 3+ phosphor s size crucially iflueces o the CRI ad CQS. From that poit of view, CaF 2 :Ce 3+, Tb 3+ ca be proposed as a potetial practical directio for maufacturig the i-cup packagig phosphor WLEDs. (Received November 10, 2017; Accepted April 2, 2018) Keywords: WLEDs; Gree-emittig, CaF 2 :Ce 3+, Tb 3+ phosphor; CRI; CQS; Mie Theory 1. Itroductio I the last few years, the white light emittig diodes (LEDs) have may advatages i eergy efficiecy, log lifetime, compactess, eviromet-friedly ad desigable features i compariso with icadescet ad fluorescet lamps. I the last few decades, the efficiecy of white LEDs lightig had already exceeded that of the icadescet lamps ad was competitive with fluorescet lamps. Without a doubt, the white LEDs lightig has bee settig foot i the lightig idustry ad dramatically challeges the covetioal lightig [1-3]. Idustrial techology system of solid state lightig maily icludes four critical techological fields: epitaxy material techology, chip desig ad maufacturig (upstream idustry), packagig materials (midstream idustry) ad process techology ad system itegratio techology ad applicatios (dowstream idustry). [1 5]. I the midstream LEDs idustry, the white light cosists of trasmitted chipemitted blue rays ad phosphor-coverted yellow rays i phosphor coatig layer. Obviously, phosphor coatig structure plays a vital role i affectig illumiatio quality of WLEDs. Packagig ot oly ca esure better performace of LED devices by ehacig reliability ad optical characteristics but ca also realize cotrol ad adjustmet of the fial optical performace [6-8]. There are may studies cocetrate o improvig the color uiformity, ad the lumious efficacy of WLEDs by cotrollig the packagig process. Moreover, the lightig properties of LEDs were sigificatly improved by usig phosphors Sr 1 -xbaxsi 2 O 2 N 2 :Eu 2+ (0x1) [9] ad by usig β-sialon:yb 2+ phosphor [11], or by varyig phosphor materials ad packagig structures[10], or by Red-Emittig Phosphor Li 2 SrSiO 4 :Eu 3+, Sm 3+ [11], by addig the red or gree phosphor to YAG:Ce phosphor compoud of W-LEDs [12-15]. The the LEDs packagig ad its materials research are the critical directios i LEDs maufacturig. * Correspodig author: trahoagquagmih@tdt.edu.v

2 346 I this research, we ivestigate the ifluece of the gree-emittig CaF 2 :Ce 3+, Tb 3+ phosphor particle s size o the color rederig idex (CRI) ad the color quality le (CQS) of the i-cup packagig MCW-LEDs. The mai cotributios of this paper ca be summarized as the followigs: 1) The gree-emittig CaF 2 :Ce 3+, Tb 3+ phosphor particle s size sigificatly affects the color uiformity of the MCW-LEDs. 2) The CRI ad CQS of MCW-LEDs ca be icreased from 58 to 66 ad 55 to 65, respectively. The rest of this research ca preset as below. The secod sectio simulates the physical model MCW-LEDs ad proposes the mathematical descriptio of the proposed model. The simulatio results are preseted, ad some discussios are proposed i the third sectios. Fially, sectio IV cocludes this paper. 2. Research Model MCW-LEDs ad Mathematical Descriptio 2.1. Physical Model WLEDs I this sectio, we simulate the real 7000K, ad 8500K MCW-LEDs by the commercial software Light Tools based o the Mote Carlo ray-tracig method (Fig. 1). I this physical model of MCW-LEDs, the reflector has a bottom legth of 8 mm, a height of 2.07 mm ad a legth of 9.85 mm at its top surface. The remote phosphor layer with a fixed thickess of 0.08 mm covers the 9 LED chips. Each LED chip with a square base of 1.14 mm ad a height of 0.15 mm is boud i the cavity of the reflector show i Fig. 1. The radiat flux of each blue chip is 1.16 W at wavelegth 455 m [12-14]. I this sectio, the size of the gree phosphor particle was chaged from 2µm to 10µm i purpose to ivestigate the effect of the gree phosphor size to the optical performace of the MCW-LEDs. I the simulatio stage i the Light Tools, we set the refractive idex of the gree ad yellow phosphors at 1.42 ad 1.83, respectively. The average radius of the phosphor particles is 7.25 μm, ad the refractive idex of the silicoe glue was chose 1.5. [12-15]. (a) (b) Fig. 1.The physical structure of the i-cup packagig WLEDs 2.2. Mathematical Descriptio of Scatterig Process For more uderstadig the tterig process of the phosphor layer, the mathematical descriptio is ecessary to propose ad demostrate by applyig Mie theory [16-22]. The tterig coefficiet μ (λ) (mm -1 ), the absorptio coefficiet μ abs (λ) (mm -1 ), aisotropy factor g(λ) (mm -1 ), ad reduced tterig coefficiet δ (λ) (mm -1 ) ca be computed by the below expressios (1), (2), (3), ad (4): ( ) N( r) C (, r) dr (1) ( ) N( r) C (, r) dr (2) abs abs

3 347 1 g( ) 2 p(,, r) f ( r)cosd cosdr (3) 1 (1 ) (4) g I these equatios, N(r) idicates the distributio desity of diffusioal particles (mm 3 ). C abs ad C is the absorptio ad tterig cross sectios (mm 2 ), p(θ,λ,r) is the phase fuctio, λ is the light wavelegth (m), r is the radius of diffusioal particles (µm), ad θ is the tterig agle ( ), ad f(r)) is the size distributio fuctio of the diffuser i the phosphorous layer. Moreover, f(r) ad N(r) ca be calculated by: f ( r) f ( r) f ( r) (5) dif phos N( r) N ( r) N ( r) K.[ f ( r) f ( r)] (6) dif phos N dif phos N(r) is composed of the diffusive particle umber desity N dif (r) ad the phosphor particle umber desity N phos (r). I these equatios, f dif (r) ad f phos (r) are the size distributio fuctio data of the diffusor ad phosphor particle. Here K N is the umber of the uit diffusor for oe diffuser cocetratio ad ca be calculated by the followig equatio: c K M () r dr (7) N Where M(r) is the mass distributio of the uit diffuser ad ca be proposed by the below equatio: 4 3 M ( r) r [ dif fdif ( r) phos f phos ( r)] (8) 3 Here ρ diff (r) ad ρ phos (r) are the desity of diffuser ad phosphor crystal [26-30]. I Mie theory, C ad C abs ca be obtaied by the followig expressios: (2 1)( ) 2 k 0 2 Cext a 2 b k 1 C a b (9) C (2 1)Re( ) (10) C C (11) abs ext Where k = 2π/λ, ad a ad b are the expasio coefficiets with eve symmetry ad odd symmetry, respectively. They ca be calculated by: ( mx) ( x) m ( mx) ( x) a ( x, m) ( mx) ( x) m ( mx) ( x) m ( mx) ( x) ( mx) ( x) b ( x, m) m ( mx) ( x) ( mx) ( x) (12) (13) Where x = k.r, m is the refractive idex, ad ( x ) ad ( x) are the Riccati - Bessel fuctio. Moreover, the phase fuctio p(,, r) ca be calculated accordig to:

4 348 4 (,, r) p(,, r) 2 k C (, ) (14) r Here (,, r) is the dimesioless tterig fuctio, which is obtaied by the tterig amplitude fuctios S ( ) ad S ( ) S2 ( ) (1/ 2)[ S ( ) ( ) ] (15) P(cos ) dp(cos ) S1( ) [ a b ] (16) ( 1) si d P(cos ) dp(cos ) S1( ) [ b a ] (17) ( 1) si d 1 Where P 1 (cos ) is the associated Legedre polyomial [16-22]. 3. Results ad discussios I this sectio, the ifluece of the gree phosphor size to the CRI ad CQS of the MCW- LEDs is preseted ad ivestigated. I the first stage, the tterig, reduce tterig, ad backtterig coefficiets of the gree phosphor i coectio with its size is simulated by the Mat Lab software. Fig. 2 illustrate the tterig coefficiet of the gree phosphor versus the particle s size. It is foud that the tterig at wavelegths of 453m, 555m crucial grew with icreasig the particle. The research results show that the quality of the white light from MCW- LEDs ca be ehaced by varyig the size of the gree phosphor particle. This ca be based o the excellet absorptio ability for the blue light from LED by the gree phosphor particle. Moreover, Fig. 3 shows the same reduced tterig coefficiet of the gree phosphor at wavelegths 453m, 555m. It idicated that the tterig stability of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor showed the great uses for cotrollig the color quality of the i-cup packagig WLEDs. Fig. 5 showed the ifluece of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor s cocetratio o the agular tterig amplitudes of the i-cup packagig WLEDs at wavelegths 453m, 555m. From the figure, we ca see huge massive ifluece of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor s cocetratio o the agular tterig amplitudes.the agular tterig amplitudes at wavelegths 453m more extesive larger tha at wavelegths 555m. From the aalysis the tterig process i the phosphor layer of the i-cup packagig WLEDs, the results idicated that the ivolvemet of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor ito the phosphor compoudig could play a major role i cotrollig the optical properties of the i-cup packagig WLEDs [15]. Fig. 2 The tterig coefficiet of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor at wavelegths of 453m, 555m.

5 349 Fig. 3 The reduced tterig coefficiet of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor at wavelegths of 453m, 555m. Fig. 4 The agular tterig amplitudes of the gree-emittig CaF 2 :Ce 3+,Tb 3+ Phosphor Fig. 5. The CQS of the 7000 K i-cup packagig MCW-LEDs by addig the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor particles Fig. 6. The CQS of the 8500 K i-cup packagig MCW-LEDs by addig the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor particles

6 350 Fig. 7. The CRI of the 7000 K i-cup packagig MCW-LEDs by addig the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor particles Fig. 8. The CRI of the 8500 K i-cup packagig MCW-LEDs by addig the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor particles Furthermore, we use the commercial Light Tools software to ivestigate the ifluece of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor s size o CQS ad CRI of the 7000K, ad 8500K icup packagig WLEDs. The size of the gree phosphor is icreased from 1µm to 10 µm cotiuously. Fig. 4 ad 5 illustrate the CQS of the 7000K, ad 8500K i-cup packagig WLEDs o the icreasig the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor s size, respectively. Furthermore, Fig. 6 ad 7 preset the ifluece of particle size o CRI of the 7000K ad 8500K i-cup packagig WLEDs. These results idicated that the CRI ad CQS crucially icreased while the size of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor rose cotiuously from 1µm to 10 µm. I this results, the ttered light of each particle i PC-LEDs is differet, resultig i varyig the optical properties of W-LEDs.. From the results, the ivolvemet ad the tterig process of the greeemittig CaF 2 :Ce 3+,Tb 3+ phosphor could be playig a essetial role i ehacig the optical properties of the i-cup packagig WLEDs. 4. Coclusios I this paper, we ivestigate the effect of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor s size o CRI ad CQS of the 7000K, 8500K i-cup packagig MCW-LEDs.From research results, the CQS ad CRI were sigificatly icreased while the size of the gree-emittig phosphor varied from 2 to 10 µm. The CRI ad CQS ca obtai the optimal value at 67 ad 65, respectively. The simulatio results ad the theoretical aalysis agreed well with each other. This research ca play the primary role i the developmet of the maufacturig MCW-LEDs i the future time.

7 351 Ackowledgmets The authors appreciate the support of Professor Hsiao-Yi Lee, Departmet of Electrical Egieerig, Natioal Kaohsiug Uiversity of Applied Scieces, Kaohsiug, Taiwa. Refereces [1] LED Packagig for Lightig Applicatios, Desig of LED Packagig Applicatios p doi: / ch6. [2] Gibey, Elizabeth, Nature 514(7521), 152 (2014). [3] Liu, Zog-Yua, Sheg Liu, Kai Wag, Xiao-Big Luo, IEEE Trasactios o Compoets ad Packagig Techologies 33(4); 680 (2010).. [4] X. Luo, R. Hu, Chip packagig: Ecapsulatio of itride LEDs. Nitride Semicoductor Light- Emittig Diodes (LEDs), (2014). [5] Luo, Xiaobig, Ru Hu, Sheg Liu, Kai Wag, Progress i Eergy ad Combustio Sciece 56, 1 (2016). [6] Y. Shuai, Y. He, N. T. Tra, F. G. Shi, IEEE Photoics Techology Letters 23(3): 137 (2011), doi: /LPT [7] Fu Xig, Huai Zheg, Sheg Liu, ad Xiaobig Luo, Frotiers of Optoelectroics 5(2) 153 (2012). [8] Yu, Reyog, Shagzhog Ji, Sogyua Ce, Pei Liag, IEEE Photoics Techology Letters 22(23), 1765 (2010). [9] S. Markus, T. Rosethal, O. Oecklera, W. Schick, Critical Reviews i Solid State ad Materials Scieces 39(3), 215 (2014). [10] L. Liu, R. J. Xie, N. Hirosaki, T. Takeda, C. Zhag, J. Li, X. Su, Sciece ad Techology of Advaced Materials 12(3), (2011). [11] H. Yu, W. W. Zi, S. La, H. F. Zou, S. C. Ga, X. C. Xu, G. Y. Hog, Materials Research Iovatios, 16(4): 298 (2012). [12] Mih, Tra Hoag Quag, Nguye Huu Khah Nha, Nguye Doa Quoc Ah, Hsiao-Yi Lee. Joural of the Chiese Istitute of Egieers 40(4), 313 (2017). [13] Mih, Tra Hoag Quag, ad Le Ah Vu. Lecture Notes i Electrical Egieerig AETA Recet Advaces i Electrical Egieerig ad Related Scieces: Theory ad Applicatio, 213 (2017). [14] Mih, Tra Hoag Quag. Iteratioal Joural of Automatio ad Smart Techology 8(1), 35 (2018). [15] Nguye Huu Khah Nha, Tra Hoag Quag Mih, Ta N. Nguye, Miroslav Vozak. Digest Joural of Naomaterials ad Biostructures 12(3), (2017). [16] Zhao, Bei, Digyi She, Qiyue Ta, Jiafeg Tag, Xiaju Zhou, Shasha Hu, Ju Yag. Joural of Materials Sciece 52(10), 5857 (2017). [17] Guo, Hai, Yue Guo, Hyeo Mi Noh, Byug Kee Moo, Sug Heum Park, Jug Hyu Jeog, Kwag Ho Kim, Joural of Naosciece ad Naotechology 16(1), 1146 (2016). [18] Zhao, Bei, Digyi She, Qiyue Ta, Jiafeg Tag, Xiaju Zhou, Shasha Hu, Ju Yag. Joural of Materials Sciece 52(10), 5857(2017). [19] Mishcheko, Michael I., Larry D.Travis, ad Adrew A. Lacis Scatterig, Absorptio, ad Emissio of Light by Small Particles. Cambridge: Cambridge Uiversity Press. [20] Zhog, Jiajia, Migyua Xie, Zhigui Ou, Rui Zhag, Mi Huag, Fuli Zhao. Mie Theory Simulatio of the Effect o Light Extractio by 2-D Naostructure Fabricatio. Symposium o Photoics ad Optoelectroics (SOPO) [21] Sommer, Christia, Frak Reil, Joachim R. Kre, Paul Hartma, Peter Pachler, Has Hoschopf, Fraz P. Wezl. Joural of Lightwave Techology 29(15), 2285 (2011). [22] Joasz, Miroslaw, Georges R. Fourier. Geeral Features of Scatterig of Light by Particles i Water. Light Scatterig by Particles i Water, p. 87, 2007.