Digest Joural of Naomaterials ad Biostructures Vol. 12, No. 3, July - September 2017, p. 891-898 Co-DOPING GREEN-EMITTING CaF 2 :Ce 3+, Tb 3+ AND YELLOW-EMITTING PHOSPHOR PARTICLES FOR IMPROVING THE CCT DEVIATION AND LUMINOUS EFFICACY OF THE IN-CUP PHOSPHOR PACKAGING WLEDs N. H. K. NHAN a, T. H. Q. MINH a,*, T. N. NGUYEN b, M. VOZNAK b 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, 708 33 Ostrava - Poruba, Czech Republic. I last few decades, Light emittig diodes (LEDs) with a series of excellece advatages is cosidered as the ext geeratioal light source. I this research, by co-dopig the Gree-emittig CaF 2 :Ce 3+, Tb 3+ phosphor to yellow-emittig YAG:Ce phosphor compoud of the 7000K ad 8500 K i-cup packagig white LED lamps (WLEDs), a iovative solutio for improvig color uiformity ad lumious efficiecy is proposed, ivestigated, ad demostrated. By usig Mie Theory with Mat Lab ad Light Tool software, the obtaied results show that the CCT Deviatio ad lumious efficacy of the 7000 K ad 8500 K i-cup phosphor packagig WLEDs crucial are iflueced by the Gree-emittig CaF 2 :Ce 3+, Tb 3+ phosphor s cocetratio. The results show that the gree-emittig phosphor ca becosider as a potetial practical solutio for maufacturig the i-cup packagig phosphor WLEDs i the ear future. (Received Jue 29, 2017; Accepted August 28, 2017) Keywords: The i-cup phosphor packagig WLEDs, Gree-emittig CaF 2 :Ce 3+,Tb 3+ Phosphor, D-CCT, Lumious efficacy, Mie Theory 1. Itroductio Light-emittig diodes (LEDs) is the modest type of solid-state lightig, which have the greatest advacemet i the lightig idustry i the last few decades [1 3]. LEDs is a solid-state light source which emits white light based o a blue die covered by the yellow or gree-red phosphor. Such a light source has bee itesively applied to geeral lightig ad replaced most light sources i geeral lightig ad eve i special lightig (automobiles, trasportatio, commuicatio, imagig, agriculture, ad medicie) owig to its may advatages [4,5]. Geerally, LEDs have the followig advatages such as eergy savig compared to other light sources, log lifetime (over 50,000 hours or more i theory), eviromet-friedly characteristics, wide rage color temperatures (4500 K 12,000 K), wide operatio temperature ( 20 C to 85 C), ad quick startup. From this poit of view, LEDs have bee cosidered as the fourth geeratio of light sources shortly [1-4]. Nowadays, the LEDs idustry chai has three mai categories: the upstream, the midstream, ad the dowstream. The upstream is the emittig layer, claddig layer, buffer layer, ad reflector. The midstream is referred to as packagig. The dowstream is coected with the product applicatio i geeral purpose. I the midstream LEDs idustry, the blue light from the blue LEDs chip should be covert ito white light by packagig. Here, the LEDs packagig are cosidered as a essetial step from LED chip to applicatios. Packagig ot oly ca esure better performaceof LED devices by ehacig reliability ad optical characteristics but ca also realize cotrol ad adjustmet of the fial optical performace [6-9]. There are may studies cocetrate o improvig the color uiformity, ad the lumious efficacy of White LED lamps (WLEDs) by cotrollig the packagig process. I [10,11] the lightig properties of LEDs were sigificatly improved by usig phosphors Sr 1 -xbaxsi 2 O 2 N 2 :Eu 2+ (0x1) * Correspodig author: trahoagquagmih@tdt.edu.v
892 ad by usig β-sialon:yb 2+ phosphor. [9], or by varyig phosphor materials ad packagig structures[10], or by Red-Emittig Phosphor Li 2 SrSiO 4 :Eu 3+, Sm 3+ [11], or by addig SiO 2 [12,13] to YAG:Ce phosphor compoud of W-LEDs. The studies show the effect of method packagig ad materials to the lightig performace of W-LEDs. From this poit of view, research about the LEDs packagig ad its materials is the importat directio i LEDs idustry. Hollow micro-ad aostructures with their uique properties such as low desity, high surface-to-volume ratio, low coefficiets of thermal expasio, ad low refractive idex, have bee applied i drug-delivery carriers, efficiet catalysis, sesors, active-material ecapsulatio, photoic crystals, ad so o [6,7]. Microstructure solid fluoride materials based o their properties (low-eergy phoos, high ioicity, electro-acceptor behavior, high resistivity, ad aioic coductivity) are used as potetial optical applicatios. Amog them, calcium fluoride (CaF 2 ) with low refractive idex ad the wide bad gap is widely applied i optoelectroic devices. Moreover, the calcium fluoride (CaF 2 ) is well-kow as the host for lumiescet ios (Ce 3+ ad Tb 3+ ) due to its high trasparecy i a broad wavelegth rage, low refractive idex, ad low phoo eergy as show i Fig. 14 [8,9]. With sigificat advatages, gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor could be cosidered as a prospective approach i WLEDs lightig [10]. Nevertheless, there have ot bee may studies, which demostrated gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor for ehacig the lumious flux ad color quatity of the i-cup packagig WLEDs as yet. This research could fill a remaiig gap. For reachig the proposed problem, the paper ca be divided ito 3 mai sectios. I the first sectio, the physical model of the i-cup packagig WLEDs is built by the commercial software Light Tools 8.4, ad the mathematical descriptio of scatterig, backscatterig ad reduced scatterig process i the phosphor layer is preseted. The secod sectio ivestigated the ifluece of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor cocetratio o the correlated color temperature deviatio (D-CCT) ad the lume output of the i-cup packagig WLEDs by the Mat lab ad Light Tools software. Fially, some discussios ad coclusios are proposed based o the research results. The research results showed that the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor particle s cocetratio sigificatly iflueced o the optical properties of the 7000K ad 8500K i-cup packagig WLEDs. 2. Physical Model WLEDs ad Mathematical Descriptio 2.1. Physical Model WLEDs To demostrate the ifluece of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor cocetratio o the correlated color temperature deviatio (D-CCT) ad the lume output of the i-cup packagig WLEDs, the physical model is ecessary to build by Light Tools. I this sectio, the i-cup packagig 7000 K, 8500 K WLEDs is simulated by usig the commercial Light Tools software based o the Mote Carlo ray-tracig method (Fig. 1). I this physical model of WLEDs, key parameters of the i-cup packagig WLEDs are defied as below: 1) The reflector: 8 mm bottom legth, a 2.07 mm height, ad a 9.85 mm legth. 2) The i-cup phosphor layer: thickess of 0.08 mm covers the 9 LED chips. 3) The LED chip: 1.14 mm square base ad a 0.15 mm height. The radiat flux of each blue chip is 1.16 W at wavelegth 455 m. I this simulatio, the cocetratio of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor particle was chaged cotiuously from 0% to 1.8%. The optical properties of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor particles are details built by usig the Light Tools 8.4 software. The refractive idex of the gree-emittig ad yellow-emittig phosphors are set at 1.80 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. The diffusioal particle desity is varied to fix the average CCT value. If the weight percetage of the diffusers is icreased, the weight percetage of YAG:Ce phosphor is ecessary to reduce to maitai the average CCT value 7000K ad 8500 K.
893 Fig. 1. The i-cup packagig WLEDs physical structure 2.2. Mathematical Descriptio of Scatterig Process For more uderstadig the scatterig process of the phosphor layer, the mathematical descriptio is ecessary to propose ad demostrate. I this sectio, applyig Mie theory [21], the coefficiets of the scatterig process of the phosphor layer of the i-cup packagig WLEDs ca be calculated as the below expressios: 1. The scatterig coefficiet μ sca (λ): ( ) N( r) C (, r) dr (1) sca Where N(r) (mm 3 ) is the distributio desityof diffusioal particles. N(r) is composed of the diffusive particle umber desity N dif (r) ad the phosphor particle umber desity N phos (r) ca be preseted as: sca N( r) N ( r) N ( r) K.[ f ( r) f ( r)] (2) dif phos N dif phos Moreover, C sca (mm 2 ) is the scatterig cross sectios. I Mie theory, C sca ca be obtaied by the followig expressio: 2 2 2 sca 2 k 0 C (2 1)( a b ) (3) Here λ (m) is the light wavelegth, ad r (µm) is the radius of diffusioal particles. 2. The aisotropy factor g(λ), 1 g( ) 2 p(,, r) f ( r)cosd cos dr (4) Where p(θ,λ,r) is the phase fuctio, f(r)) is the size distributio fuctio of the diffuser i the phosphor layer, θ ( ) is the scatterig agle. 3. The reduced scatterig coefficiet δ sca (λ): I these equatios, f(r) ad N(r) ca be calculated by: 1 (1 ) (5) sca sca g f ( r) f ( r) f ( r) (6) dif Where 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: phos
894 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. Where k = 2π/λ, ad a ad b are calculated by: ( mx) ( x) m ( mx) ( x) a ( x, m) ( mx) ( x) m ( mx) ( x) (9) m ( mx) ( x) ( mx) ( x) b ( x, m) m ( mx) ( x) ( mx) ( x) (10) Where x = k.r, m is the refractive idex, ad () x ad ( x) are the Riccati - Bessel fuctio. The below equatio ca express the phase fuctio: 4 (,, r) p(,, r) (11) (, r) 2 k Csca Where (,, r), S 1 (θ) ad S 2 (θ) are calculated by below equatios: 1 2 2 (,, r) [ S1( ) S2( ) ] 2 (12) 2 1 a( x, m) (cos ) S1 1 ( 1) b( x, m) (cos ) (13) S 2 2 1 a( x, m) (cos ) 1 ( 1) b( x, m) (cos ) (14) I equatios (13) ad (14), ad are the agular depedet fuctios [17-23]. 3. Results ad discussio I Fig. 2, the scatterig coefficiet of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor at wavelegths of 453m, 555m crucial grew with icreasig the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor s cocetratio. It meas that the white-light quality ca be ehaced by cotrollig the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor particle s cocetratio. The gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor has a great absorptio ability for the blue light from LED. O the aother had, the reduced scatterig coefficiet of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor at wavelegths 453m, 555m are the same with each other i depedig o the cocetratio (Fig 3). Itidicated that the scatterig 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 scatterig amplitudes of the i-cup packagig WLEDs at wavelegths 453m, 555m. From the figure, we ca see the huge ifluece of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor s cocetratio o the agular scatterig amplitudes. The agular scatterig amplitudes at wavelegths 453m are larger tha at wavelegths 555m. From the aalysis the scatterig 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. 895 Fig. 2. The scatterig coefficiet of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor at wavelegths of 453m, 555m. Fig. 3 The reduced scatterig coefficiet of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor at wavelegths of 453m, 555m. Fig. 4 The agular scatterig amplitudes of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor at wavelegths of 453m, 555m.
896 Fig. 5. The CCT deviatio 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 CCT deviatio of the 8500 K i-cup packagig MCW-LEDs by addig the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor particles Fig. 7. The lumious flux 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 lumious flux of the 8500 K i-cup packagig MCW-LEDs by addig the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor particles
I this sectio, we use the commercial program Light Tools 8.4 to ivestigate the effect of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor s cocetratio o the optical properties (D-CCT ad lumious flux) of the 7000K ad 8500K i-cup packagig WLEDs. The cocetratio of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor is icreased from them 0% to 1,8 % cotiuously. Fig. 4 ad 5 showed the D-CCT of the 7000K ad 8500K i-cup packagig WLEDs o the icreasig the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor s cocetratio, respectively. The D-CCT decreased from 4000K to 1250 K for the 7000K WLEDs cases, ad from 9600K to 2100K for the 8500K WLEDs. I this situatio, the D-CCT could be decreased more tha 3 times. Furthermore, Fig. 6 ad 7 showed the ifluece of particle cocetratio o lumious efficacy of the7000k ad 8500K i-cup packagig WLEDs. These results idicated that the lumious flux crucially icreased while the cocetratio of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor rose cotiuously from 0% to 1.8%. The lumious flux rose from 800 lm to 1600 lm i the 7000K WLEDs, ad from 900 lm to 1700 lm i the 8500K WLEDs. The results provided that the lumious efficacy ca ehace more tha 2 times whe we added the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor to the phosphor compoudig. I this results, the scattered light of each particle i PC-LEDs is differet, resultig i varyig the optical properties of W-LEDs. I this situatio, the CCT deviatio ca be reduced sigificatly i coected with the scattered blue light is ehaced eough iside. From the results, the ivolvemet ad the scatterig process of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor could be playig a importat role i ehacig the optical properties of the i-cup packagig WLEDs [17]. 897 4. Coclusios I this research, the ifluece of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor s cocetratio o the D-CCT ad the lumious efficacy of the 7000K ad 8500K i-cup packagig WLEDs was proposed ad demostrated totally. From results ad theory aalysis, some coclusios ca be proposed: 1) CCT deviatio ca be decreased more tha 3 times with risig cocetratio of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor particles. 2) The lumious efficacy had a icrease more tha 2 times i coectig with risig cocetratio of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor particles. This study provided a potetial techical implicatio for W-LEDs maufacturig ad material developmet for WLEDs applicatios i theear future. I the future work, the ifluece of both size ad cocetratio of the gree-emittig CaF 2 :Ce 3+,Tb 3+ phosphor particles o the optical properties of WLED with differet packagig is ecessary to propose ad demostrate. Ackowledgemets 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. 2011. Desig of LED Packagig Applicatios, 215 315. doi:10.1002/9780470827857.ch6. [2] Elizabeth Gibey, Nature 514(7521), 152 (2014). [3] Zog-Yua Liu, Sheg Liu, Kai Wag, Xiao-Big Luo, IEEE Trasactios o Compoets ad Packagig Techologies 33(4), 680 (2010). [4] Chig-Cherg Su, Yu-Yu Chag, Tsug-Hsu Yag, Te-Yua Chug, Cheg-Chie Che, Tsug-Xia Lee, Du-Ru Li, et al. Joural of Solid State Lightig 1(1), 19 (2014). [5] E. F. Schubert, Sciece 308(5726), 1274 (2005). [6] X. Luo, R. Hu, Chip packagig: Ecapsulatio of itride LEDs. Nitride Semicoductor
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