Session: LED Phosphors Luminescent Materials for LEDs with Ultimate Efficiency y and Color Q Quality y By Prof. Dr. Thomas Jüstel Department Head Chemical Engineering Münster University of Applied Sciences Almost 20% of produced electrical energy is consumed by lighting ((source: NASA)) in 1989 “The wind of change” 21st Development of daylight white LEDs with century luminous efficiency > 120 lm/W replacement of Na and Hg low and high pressure discharge lamps 2014 “The light of change” East Berlin Na lamps West Berlin Hg lamps Outline 1. Advances in LED Technology 2. White Light Generation 3. Luminescent Materials (Phosphors) 4. Phosphor Converted LEDs (pcLEDs) 5. Towards Ultimate Efficiency and CRI 6. Conclusions and Outlook 1. Advances in LED Technology 1970 2014 (Ga,As)P < 0.1 01W < 1.0 lm < 10 lm/W < 120 °C C < 100 W/cm2 > 120 K/W Yellow red, Yellow, red NIR (Al,In,Ga)P, (In,Ga)N, (Al,Ga)N 06-5W 0.6 > 100 lm up to 303 lm/W (CREE) 120 – 200 °C C 100 – 200 W/cm2 2 – 12 K/W All colours and UV! (Al,In,Ga)P 580 nm – 700 nm Yellow Orange Red ( , ) (In,Ga)N 370 – 530 nm UV-A Blue Green (Al,Ga)N 210 – 370 nm UV-C UV-A Emission intens sity [a.u.] 1. Advances in LED Technology 0,35 0,30 0,25 0,20 0,15 , 0,10 0,05 0,00 400 450 500 550 600 650 700 750 Wavelength [nm] • • • All spectral colours by LEDs without colour filter accessible! EL of semiconductors results in emission bands with small FWHM < 30 nm But white light cannot be efficiently produced by a single LED type so far.... far 1. Advances in LED Technology Technical Status 2014 Lumen output: CRI: Liftime: Design: > 200 lm/W (cool white) > 100 lm/W (warm white) 70 – 95 > 30000 h Very flexible Presently: Retrofits für fluorescent tubes and light bulbs Advantages of LED over Incandescent lamps Higher g lifetime Higher effiziency Better robustness No IR radiation Fluorescent lamps (CFL +TL) Simpler p driving g and dimming g Higher colour rendering Better robustness No UV radiation 2. White Light Generation General concepts 1. Gl 1 Glowing i solids lid 2. Gas discharges 3. Semiconductors visible i ibl light li h + IR VUV + UV-C/B/A + visible light UV-A or visible light g or IR-A White Green colour filter Coloured light by absorption Red Blue Y or YR or RG phosphor White light by additive colour mixing (V)UV CO or RGB phosphor blend White light by luminescence 2. White Light Generation Red + Green + Blue LEDs Blue LED + yellow phosphor Blue LED + RG phosphor blend UV LED + RGB phosphor blend 2. White Light Generation 99.5 99 98 Multichip LEDs • • • Narrow band emitter – ½ = 30 nm typical 95 90 – 2 - 5 monochromatic LEDs 80 Theoretical limit 70 – 430 lm/W with 60 Source: Zukauskas, A., et. al.., 50 "Optimization of white polychromatic – CCT = 4870 K 40 semiconductor lamps", Applied y Letters 80 ((2002)) 234-6 Physics 30 – CRI = 3 (!) 20 Possible values 10 – 360 lm/W for CRI 90, n = 3 - 4 5 – 320 lm/W l /W for f CRI 99 99, n = 5 0 Problems 300 350 400 Lumen output [lm/Welectric] – Thermal q quenching g of (Al,In,Ga)P ( ) – LED Efficiency • Red / Blue high • Green low “The The green gap gap” Colour rend C dering • 5 LED 4 LED 3 LED 2 LED 450 2. White Light Generation 440 - 490 nm LED Chip 440 - 490 nm Luminescent Screen LED Chip 440 - 490nm Luminescent Screen 300 – 350 lm/Wopt. 250 – 300 lm/Wopt. 280 – 330 lm/Wopt. CRI = 70 – 85 CRI = 85 – 95 CRI = 80 – 85 low CRI at low Tc high CRI at low Tc but decreases with Tc CRI ~ independent of Tc single phosphor screen phosphor blend phosphor blend 2. White Light Generation Blue band emitter + green + red converter 90 100 88 98 86 96 84 CR RI Luminous e L efficacy [lm m/W] 102 82 94 80 92 78 90 440 450 460 470 480 490 Wavelength [nm] Conclusion: Blue LEDs emitting in the range 460 – 470 nm yield best compromise between CRI and luminous efficacy 2. White Light Generation Emission of lines or narrow bands in the blue and or red desired…. InGaN LED / Eu2+ Eu2+/ Eu3+/Mn4+ Lumen output of a light source Strongly dependent on emission spectrum • Optimal for pure 555 nm radiation – V() = 683 lm/W ( = 100%) • Luminous L i flux fl – 1000 lm for 555 nm requires solely 1.5 W radiation – „green light“ li ht“ • Blue and red radiation – V() < 70 lm/W (<10%) – reduces lumen equivalent – is required for generating white light with high CRI Lumen output [ lm/W ] • [ nm ] 3. Luminescent Materials (Phosphors) Definition An (inorganic) luminescent material (phosphor) is a material which converts t absorbed b b d energy into i t electromagnetic l t ti radiation di ti beyond b d thermal equilibrium Emission Excitation Heat Heat Heat D A S Layer of Y3Al5O12:Ce µ-particles ET ET A Emission Heat ET ET A Heat Average particle size ~ 1 – 10 µm 3. Luminescent Materials (Phosphors) Type of converter materials Norm malised emission n intensity 1. Inorganic phosphors Microscale powders SrYSi4N7:Ce (Ba,Sr)2SiO4:Eu (Ca,Sr,Ba)Si2N2O2:Eu SrYSi4N7:Eu (Y,Gd,Tb,Lu)AG:Ce CaAlSiN3:Ce (Ca,Sr)2SiO4:Eu (Ca,Sr)S:Eu (Ca,Sr,Ba)2Si5N8:Eu 1,0 (Ca,Sr)AlSiN3:Eu Nanoscale powders 0,8 ((Y,Gd,Tb,Lu)AG:Ce , , , ) Quantum dots 0,6 (Zn,Cd)(S,Se), (In,Ga)(P,As), 2. Organic dyes 0,4 Polycyclic aromatic compounds Perylenes 0,2 Coumarines Metal complexes 0,0 Ln3+-complexes Ln = Tm, Tb, Eu 300 R and Rud Ir-complexes I l 400 500 600 Wavelength [nm] 700 800 3. Luminescent Materials (Phosphors) Garnets • (Y,Tb)3Al5O12:Ce • Lu3Al5O12:Ce • Lu3(Ga,Al)5O12:Ce • (Lu,Y)3Sc2Al3O12:Ce • ((Y,Lu) , u)3((Al,Mg,Si) , g,S )5O12:Ce Ce • Ca(Y,Lu)2Al4SiO12:Ce Ortho-silicates • (Ca,Sr,Ba)2SiO4:Eu • (Ca,Sr,Ba)3SiO5:Eu (Oxy)Nitrides • (Sr,Ca,Ba) (Sr Ca Ba)2Si5N8:Eu • (Sr,Ca,Ba)Si2N2O2:Eu • (Ca,Sr)AlSiN3:Eu • (Ca,Sr,Ba)SiN (Ca Sr Ba)SiN2:Eu • La3Si6N11:Ce • Ba3Si6O12N2:Eu • ,ß-SiAlONes:Eu ß SiAlONes:Eu Selection criteria for LED phosphors • Patent situation • Price and access • (Photo)Chemical stability • Colour point stability • Conversion efficiency (IQA and EQA) • Thermische quenching • Absorption strength • Saturation/Linearity • Environmental issues „2-5-8 2-5-8“ „1-2-2-2“ „1-1-1-3“ „1-1-2 1-1-2“ „3-6-11“ 4. Phosphor Converted LEDs High Power LEDs low thermal resistance ~ 2-3 K/W typical phosphor contact plastic lens InGaNsemi- gold wire conductor cooling element (Cu) (In,Ga)N semiconductor + phosphor (converter) Bl 420 – 480 nm Blue Y ll Yellow Yellow + Red Green + Red N Near UV 370 – 420 nm Bl + Green Blue G + Red R d Colour temperature range cooll white hit warm white cool and warm white cooll and d warm white hit 4. Phosphor Converted LEDs Luminescent screen (In,Ga)N LED Yellow/orange phosphor 70 3+ Em mission inte ensity Tc = 4490 K CRI = 79 Yelllow Converterr 50 0,6 0,4 0,2 , 0,0 400 Tc = 5270 K CRI = 82 60 0,8 Blue OLED B Emission intensity [a.u.] 2+ Ce or Eu Phosphor 1,0 450 500 550 600 Tc = 4110 K CRI = 76 40 Tc = 3860 K CRI = 73 30 Tc = 3540 K CRI = 70 20 10 650 Wavelength [nm] 700 750 800 0 400 500 600 Wavelength [nm] Status quo cool white pcLEDs @ 2014 • Phosphor (Y,Gd,Tb,Lu)3Al5O12:Ce3+ (Ca,Sr,Ba)2SiO4:Eu2+ • Luminous efficacy LE = 303 lm/W! (WPE ~ 80%) • Colour rendering index CRI ~ 70 - 80 • Corr. Corr colour temperature Tc > 5000 K 700 800 4. Phosphor Converted LEDs Yellow Converters Ortho-Silicates A2SiO4:Eu, Sr2LiSiO4:Eu Oxynitrides y ((Ca,Sr)Si ) 2N2O2:Eu -SiAlONes -SiAlON:Eu Garnets Oxynitrides Nitrides A3B2B’3O12:Ce (Sr1-xBax)2SiO4:Ce,N La3Si6N11:Ce Sr2Si5N8:Ce Gd2(CN2)3:Ce C C Cyanamides id 470 – 525 nm 560 nm 535 nm 540 nm UCSB Mitsubishi Philips U iTübi UniTübingen/Münster /Mü t 3+ 3+ Gd2(CN2)3:Ce 6 Gd2(CN2)3:Ce 6 3+ Ce 4f-5d (412 nm) 540 nm 5 Intensity [10 counts] 4 5 Intensitty [105 counts] 5 3 2 3 2 1 1 0 250 4 275 300 325 350 375 400 Wavelength [nm] 425 450 475 500 Sample: 174b 0 400 425 450 475 500 525 550 575 Wavelength [nm] 600 625 650 675 Sample: 174b 4. Phosphor Converted LEDs CRI Enhancement and colour temperature reduction of pcLEDs 4 LUXEON LEDs (Philips Lumileds) (I G )N LED Y3Al5O12:Ce (In,Ga)N C 1.2 4 R d phosphor Red h h JAZZ 3300K 4 BB 3300K 4 1 4 4 08 0.8 4 0.6 4 5 0.4 0 400 0.2 450 500 550 600 650 nm 700 750 0 400 450 500 550 600 650 700 750 nm 800 Wavelength [nm] black body 3600 K Status quo warm white pcLEDs @ 2014 fluorescent, CCT=3600 K • Red phosphor Eu2+ activated • Luminous efficacy LE 80 - 150 lm/W • Colour rendering index CRI 85 – 95 • Corr. colour temperature Tc 2500 - 4000 K R. Mueller-Mach, G.O. Mueller, P.J. Schmidt, T. Jüstel, R dD Red Deficiency fi i Compensating C ti Phosphor Ph h LED , Light Li ht Emitting E itti D Device, i US P Patent t t 20030006702 400 450 500 550 600 650 700 750 nm 800 4. Phosphor Converted LEDs Red emitting LED phosphors Eu2+ doped nitrides 585 nm 625 nm 650 nm Ba2Si5N8:Eu Sr2Si5N8:Eu CaAlSiN3:Eu 1,0 Emiss sion intensity y [a.u.] Ba2Si5N8:Eu Sr2Si5N8:Eu C 2Si Ca S 5N8:Eu (Ca,Sr)AlSiN3:Eu CaAlSiN3:Eu 0,8 0,6 04 0,4 0,2 0,0 500 550 600 650 Wavelength [nm] 700 750 800 4. Phosphor Converted LEDs 1,0 Emission spectrum Excitation spectrum ### 1,0 Emission intensity y [a.u.] Blue LED + Green + Red (band emitter) CRI will only y slightly g y depend p on Tc 0,8 0,6 0,4 0,8 0,0 200 300 400 500 600 700 800 0,4 0,2 0,0 400 Emission spectrum Excitation spetrum 1,0 0,8 Relative intensity 0,6 Red Converrter Green Conv G verter Wavelength (nm) Blue LED Emission intensity [a.u.] 0,2 0,6 0,4 0,2 450 500 550 600 650 700 Wavelength [nm] 750 800 0,0 200 300 400 500 600 700 800 Wavelength [nm] Green emitter G itt ortho-Silicates th Sili t (AE = Ca, Sr, Ba) Oxynitrides ß-SiAlONes Garnets CaSi2N2O2 - SrSi2N2O2 Solid AE2SiO4:Eu E AESi2N2O2:Eu solution without miscibility gap fine-tuning of green emission ß-SiAlON:Eu band position possible Lu3Al5O12:Ce 4. Phosphor Converted LEDs First all nitride LED demonstrated in 2005 (QE > 0.9, QErel(200 °C) > 0.95) (In,Ga)N LED + SrSi2N2O2:Eu + (Sr,Ca,Ba)2Si5N8:Eu Colour rendering index > 88 Excellent colour point stability with drive is achieved Drive at 25 °C 2.50E-06 1.11E-01 4.75E-01 2.00E-06 1.92E+00 1.50E-06 2.78E+00 4 09E+00 4.09E+00 1.00E-06 5.01E-07 CCT, K 1.30E+00 5000 4500 4000 3500 3000 2500 2000 1500 1000 500 0 99 97 95 93 91 89 87 85 0 1.00E-09 380 Ra 3.00E-06 1 2 3 4 5 Current , A (pulsed) 430 480 530 580 630 680 730 780 CCT_25C CCT_125C Ra_25C R. Mueller-Mach, G.O. Mueller, M.R. Krames, H.A. Höppe, F. Stadler, W. Schnick, T. Jüstel, P.J. Schmidt, All Nitride White Light Emitting Diodes, Phys. Stat. Sol. A 202 (2005) 1727 Ra_125C 4. Phosphor Converted LEDs Eu2+ and Yb2+ Phosphors Emission at 1,0 490 nm 540 nm 565 nm 580 nm 610 nm 630 nm 650 nm 650 nm Relative e intensity Phosphor Eu2+ [Xe]4f7 BaSi2N2O2:Eu SrSi2N2O2:Eu CaSi2N2O2:Eu Ba2Si5N8:Eu Sr2Si5N8:Eu (Ca,Sr)AlSiN3:Eu Ca2Si5N8:Eu CaAlSiN3:Eu Excitation and emission spectrum of SrSi2N2O2:Yb2+ Band edge d 0,8 0,6 14 0,4 13 1 4f - 4f 5d 0,2 0,0 100 Yb2+ [Xe]4f14 Cam/2Si12 12-m-n m nAlm m+n nOnN16 16-n n:Yb 550 nm SrSi2N2O2:Yb 615 nm 200 300 400 500 600 700 800 Wavelength [nm] M. Mitomo, K. Uheda et al., J. Phys. Chem. B 109 (2005) 9490 Problem: Thermal quenching V. Bachmann,, T. Jüstel,, A. Meijerink, j , C.R. Ronda,, P.J. Schmidt,, J. Luminescence (2006) ( ) 4. Phosphor Converted LEDs Thermal quenching of a typical LED converter material 2+ Mitsubishi CaAlSiN3:Eu (0,7%) 350 K 400 K 450 K 500 K 550 K 600 K 650 K 700 K 750 K 500000 400000 2+ SSL-EX-037 CaAlSiN3:Eu 70000000 Boltzmann fit of Data14_B Emissions sintegral [counts] 600000 Intensität [a.u.] 2+ Mitsubishi CaAlSiN3:Eu (0,7%) 300000 200000 100000 60000000 Chip-Tempe eratur-Bereich 700000 50000000 40000000 30000000 20000000 10000000 0 0 500 600 Wellenlänge [nm] 700 800 300 400 500 600 700 800 Temperatur [K] • Thermal quenching is a reversible process and occurs for all kind of phosphors • The quenching temperature is a strong function of the activator, host, and its interaction 5. Towards Ultimate Efficiency and CRI Eu2+ Tb3+ Ln3+ Mn2+ Mn4+ Causes for the reduction in luminous efficacy Spectral interaction due to re re-absorption absorption 2. Reduction in lumen equivalent y [ lm/W ] 1 1. „Waste“ [ nm ] Band width [nm] 90 - 120 Position (nm) 635 LE (lm/W) Red LED Phosphor 257 (Ca,Sr)S:Eu (Ca,Sr,Ba)2Si5N8:Eu (Ca,Sr)AlSiN3:Eu 20 – 30 655 278 Mg2TiO4:Mn4+ 20 – 30 620 320 Ln3+ activated (Ln = Pr, Sm, Eu) Mn4+ activated 50 – 60 655 269 Eu2+- activated 50 – 60 620 300 Eu2+- activated A. Zukauskas et al., Appl. Phys.Lett. 93 (2008) 051115 5. Towards Ultimate Efficiency and CRI Narrow-band red-emitting Sr[LiAl3N4]:Eu2+ as a next-generation LED-phosphor material material” W. Schnick et al., Nature Materials (2014) 1-6 Appeared on-line June 22nd Synthesis LiAlH4 + (1-x) SrH2 + x EuF3 + 2 AlN + N2 (S (Sr1-x ux)[ )[LiAl3N4] + 3 3x HF + (3 (3-x)) H2 1 xEu RF-furnace, 1000 °C Optical p Properties p max = 651 nm for 5% Eu2+ FWHM = 1180 cm-1 QE(200 °C) > 95% of QE(RT) Decay time Eu2+ ~ 1.1 µs Exc. @ 410 nm Photoionisation! Strong re-absorption of YAG/LuAG PL 5. Towards Ultimate Efficiency and CRI LED Converter (GE Patent US2006/0169998) Problems: Blue 420 – 480 nm Chip p Yellow (Y,Gd,Tb,Lu)Al5O12:Ce Red Mn4+- phosphor Tb3Al5O12:3%Ce + K2[TiF6]:Mn4+ Absorption strength, decay time and stability of red line emitter 5. Towards Ultimate Efficiency and CRI CaAlSiN3:Eu (Mitsubishi Chemicals) Reduced re-absorption to increase package gain 6 1 [Xe]4f 5d 7 - [Xe]4f 0,8 0,6 0,4 0,2 Emission spectrum Excitation spectrum 0,0 300 400 500 600 700 800 Wavelength [nm] 3+ Red emitting ion Eu2+ Eu3+ Sm3+ Pr3+ Mn4+ Cr3+ Fe3+ LE [lm/Wopt.] 80 - 200 220 – 360 240 – 260 200 – 220 80 – 150 < 100 < 100 NaGdW2O8:Eu (60%) Emission spectrum Excitation spectrum 1,0 Norma alised intensity [a a.u.] • 1,0 Norm malised intensity [[a.u.] Challenges • Red narrow band or line emitter to increase lumen equivalent QE465 = 48.1% RQ465 = 75.8% QE394 = 54.8% 0,8 RQ394 = 63.5% 0,6 x = 0.668 y = 0.331 LE = 268 lm/W max = 616 nm 0,4 centroid= 627 nm 0,2 0,0 300 400 500 600 Wavelength [nm] 700 800 5. Towards Ultimate Efficiency and CRI Eu3+ doped Molybdates, e.g. LiLaMo2O8:Eu and Tb2Mo3O12:Eu Luminescence spectra 10 1,0 T-dependent integral emission intensity Emission spectrum Excitation spectrum 5% 6 0,6 0,4 0,2 0,0 250 300 350 400 450 500 550 600 650 700 750 Wavelength [nm] 1,0 Normalized Intensity 100% Eu3+ • Integral intensity Emisssion maxima [Cou unts] Normalised d intensity 0,8 6 5x10 Eu3+ 4x10 6 3x10 6 2x10 6 1x10 0 100 200 300 400 500 Temperature [K] 0,5 0,0 250 300 350 400 450 Wavelength [nm] 500 550 600 QE465 ~ 100% R465 = 75% R395 = 60% CIE x = 0.665 CIE y = 0.333 LE = 269 lm/Wopt max = 614 nm centroid = 623 nm 1/e = 0.39 ms (0.2 x Y2O3:Eu) d50 = 4.2 µm • Patent Application Publication US2007/0090327, “Novel red fluorescent powder”, Industrial Technology Research Institute, Taiwan • M. Rico, U. Giebner, et.al, “Growth, spectroscopy, and tunable laser operation of the disordered crystal LiGd(MoO4)2 doped with ytterbium”, J. Opt. Soc. Am. B 22 (2006) 1083 5. Towards Ultimate Efficiency and CRI 465 nm InGaN LED 0,5 1,0 0,5 Tb3+ 0,0 400 Normaliz zed Intensity [~counts] 465 nm LED + Tb2Mo3O12:Eu3+ (40%) ceramic 465 nm LED 450 1,0 500 550 400 380 nm LED 450 500 550 Wavelength [nm] 600 650 700 750 0,0 800 1,0 380 nm LED + Tb2Mo3O12:Eu3+ (40%) ceramic 0,5 0,5 0,0 360 380 400 420 350 400 450 500 Wa elength [nm] Wavelength 550 600 650 700 750 0,0 800 Norma alized Intensity [[~counts] 380 nm InGaN LED Full conversion LED poss possible be 1,0 Normalized Inten N nsity [~counts] Normalized In ntensity [~counts s] Phosphor converted LED comprising Tb2Mo3O12:Eu 5. Towards Ultimate Efficiency and CRI LE and CRI calculations of warm-white phosphor converted LEDs Tb2Mo3O12:Eu gives 20% higher LE compared to SrLiAl3N4:Eu The reduced rere absorption in Eu3+ phosphor comprising i i LEDs LED gives potentially higher package gain as well ….. 5. Towards Ultimate Efficiency and CRI Powder/polymer composites Ceramics Variable layer thickness Strong scattering High thermal resistance Drop-Stop Homogeneous layer thickness Little scattering Low thermal resistance Pick & Place Blue LED + inorganic luminescent powder in epoxy- or silicon resin Blue LED + ceramic converter (Lumiramic or c2) 5. Towards Ultimate Efficiency and CRI Eu3+ doped molybdates as red colour converter in white-emitting pcLEDs Useful in near UV emitting LEDs (380 - 420 nm) Conversion C i off red d emitting itti powders d into i t ceramics i 1,0 LiEuMo2O8 LED Max = 394 nm LED Max= 464 nm Intensity [a.u u.] 0,8 0,6 0,4 0,2 0,0 250 300 350 400 450 Wavelength [nm] 500 550 6. Summary and Outlook LiEuMo2O8, Li3Ba2Eu3Mo8O32, Tb2Mo3O12:Eu (Sm) - Are these luminescent converters applicable in white light emitting pcLEDs? + + + + + Cost effective and scalable synthesis routes ~ 20% higher lumen equivalent than Eu2+ doped sulphides and nitrides Quantum yield at ambient temperature close to unity Less than 20% thermal quenching upon heating to 150 °C Reasonable absorption strength between 370 and 410 nm - Narrow a o width dt of o absorption abso pt o 4f-4f line e multiplets u t p ets Diffuse reflectance at 465 and 535 nm still 70 - 80% Useful in pcLEDs comprising a near UV emitting (In (In,Ga)N Ga)N die (370 – 410 nm) as a pump source Further optimisation by ceramic preparation or multiple activator ion sites, as inTb2MoO6:Eu 6. Summary and Outlook Warm white LEDs Blue chip p Ln3Al5O12:Ce CaS:Eu/Sr2Si5N8:Eu CaAlSiN3:Eu Red line emitters Eu3+ doped molybdates/tungstates • Strong absorption at 395, 465, 535 nm • Quantum efficiency ~ 100% • Problem: Absorption strength in the blue weak compared to CaS:Eu and Sr2Si5N8:Eu Warm White LEDs (near UV) Blue/cyan y luminescent material Ln3Al5O12:Ce CaS:Eu/Sr2Si5N8:Eu/CaAlSiN3:Eu Eu3+-doped doped molybdates LiLaMo2O8:5%Eu 1,0 0,8 Relative intensity Cool white LEDs 1. Blue chip p 2. Ln3Al5O12:Ce 3. None 3+ 5 Emission spectrum Excitation spectrum Reflection spectrum QE465 = 41% 7 D0 - FJ RQ465 = 65% 0,6 04 0,4 0,2 0,0 150 Next steps Wavelength [nm] • Increase average particle size to enhance absorption strength • Final goal: Transparent ceramics? • Development of further stable green green, yellow and red line phosphors with high luminous efficiency 200 250 300 350 400 450 500 550 600 650 700 750 Sample DU084-06 6. Summary and Outlook Increase of the power density 8000 lm module (CREE) Further p power density y increase will require phosphors with improved linearity Optical power density o of LED [W W/cm2] 1000 100 10 1 0.1 0.01 0.001 1960 1970 1980 1990 2000 Year Development of the power density of LED (source: fairchildsemi.com) fairchildsemi com) 2010 Acknowledgement • Research Group “Tailored Optical Materials“ for synthesis, photographs, spectroscopy, and so on…. • University Tübingen, Germany Prof. Jürgen Meyer for inspiring discussions on solid state chemistry • Universiteit Utrecht, The Netherlands Prof. Andries Meijerink for fruitful discussions on luminescence physics • FEE Idar-Oberstein for crystal growth and fr itf l collaboration on laser gain media fruitful • Merck KGaA Darmstadt for generous financial support pp
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