Research Article Color Rendering Index Thermal Stability...

Research ArticleColor Rendering Index Thermal Stability Improvement ofGlass-Based Phosphor-Converted White Light-Emitting Diodesfor Solid-State Lighting

Chun-Chin Tsai

Department of Optoelectronic Engineering Far East University Tainan 744 Taiwan

Correspondence should be addressed to Chun-Chin Tsai tsaichunchingmailcom

Received 29 January 2014 Revised 18 March 2014 Accepted 1 April 2014 Published 5 June 2014

Academic Editor Ray-Hua Horng

Copyright copy 2014 Chun-Chin Tsai This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

High color rendering index performance has been required for phosphor-converted warm-white light-emitting diodes (PC-WWLEDs) in lighting industry The characteristics of low-temperature fabricated phosphor (yellow Ce3+YAG green Tb3+YAGand red CaAlClSiN

3Eu2+) doped glass were presented for applications to high color rendering index warm-white-light-emitting

diodes Color coordinates (x y) = (036 029) quantum yield (QY) = 556 color rending index (CRI) = 853 and correlated colortemperature (CCT) = 3923K were characterized Glass-based PC-WWLEDs was found able to maintain good thermal stability forlong-time high-temperature operation QY decay CRI remenance and chromaticity shift were also analyzed for glass- and silicone-based high-power PC-WLEDs by thermal aging at 150∘C and 250∘C for industrial test standardrsquos aging time 1008 hours Better thanthe siliconersquos thermal stability of glass-based PC-WLEDs has been improved The resulted high color rendering index (CRI) glassphosphor potentially can be used as a phosphor layer for high-performance and low-cost PC-WLEDs used in next-generationindoor solid-state lighting applications

1 Introduction

For liquid crystal displays and outdoor lightings white light-emitting diodes (WLEDs) have been extensively used asbacklight source due to their eco-friendly features compactsize and high reliability compared to conventional lightsources such as incandescent bulbs and fluorescent lamps[1ndash4] The so-called ldquowhite lightrdquo emission can be typicallygenerated by the mixture of three primary colors (redgreen and blue) or two complimentary colors (eg blue andyellow) based on the principle of additive color mixing [5ndash7] Subjected to the physical structure ofWLEDmodules thestrategy of realizing white light can be categorized into twomajor technologies (1) combination ofmultiple LEDs and (2)phosphor-converted LEDs (PC-LEDs) In the first strategyof white light emission two or three monochromatic LEDsare used to generate preferred white light Dynamic colorcontrol is achievable by electronically adjusting the drivingcurrent of each LED individually Its high quantum efficiencyis also an advantage of the multiple LEDs technique without

Stokes shift which is due to photonic energy downconversion[8 9] However cost of multiple LEDs technique is muchhigher than other techniques so multiple LEDs techniqueis only used in some special applications Therefore PC-LEDs technology dominates the market today because ofsignificantly low cost compact structure and simple drivingcircuit although the quantum efficiency of PC-LEDs isslightly lower than that of multiple LEDs PC-LEDs are ina configuration with a short-wavelength-emitting LED asthe excitation sources in the visible [10 11] andor UV [1213] spectral regimes and a wavelength converter such asphosphor which converts the light from excitation sourcesto generate white light The correlated color temperature andcolor rendering property of the PC-LEDs can be determinedupon the composition and concentration of the phosphorin the wavelength converters Full development of phosphormaterials significantly contributed to LED lightings Yellowphosphors such as broadband YAG phosphors have beenextensively studied on the integration with the complemen-tary blue LEDs to form white light However color rendering

Hindawi Publishing CorporationInternational Journal of PhotoenergyVolume 2014 Article ID 407239 6 pageshttpdxdoiorg1011552014407239

2 International Journal of Photoenergy

Computer system Glass phosphor

Integrating sphere

Sensor

Fiber sensor

LED tester LED-645

20W blue LED

Figure 1 The test chamber schematic for optical measurement

index (CRI) of theWLEDs is usually less than 70 which is notacceptable for general interior illumination and some speciallighting including medical applications and architecturallighting To achieve high color rendering properties multi-phosphors such as redyellow and orangeyellow have to beadded into the color conversion layer Multiphosphor-dopedsilicone as the color conversion layer of the high-CRI WLEDhas been fabricated to demonstrate the above purpose [14 15]but the poor thermal stability of the silicone matrix weakensthe superiority for high-luminance lighting applications dueto the lower glass transition temperature of silicone (150∘C)In the previous works for yellow light emission to mix withblue light from LED we have demonstrated novel glass-basedphosphorswith excellent thermal stability for the applicationsof high-power WLEDs [16] but the resulted CRI values werenormally as low as 70s with single phosphor powder

Remote phosphor was studied as an alternative technol-ogy for white light LED Kuo et al investigated patternedstructure of remote phosphor for phosphor-converted whitelight LEDs [17] This patterned structure was designed toreduce the angular-dependent correlated color temperature(CCT) Intematix Company reported polycarbonate-basedremote phosphor layer around source LED [18] though glass-based remote phosphor product could be under develop-ment

In this study we fabricated a thermally stable multi-phosphor-doped glass (MPDG) for the goal The resultsshowed that the glass-based PC-WLEDs exhibited goodthermal stability in lumen loss chromaticity shift CRI andQE characteristics Then we compared with the silicone-based high-power PC-WLEDs under thermal aging at lowertemperature of 150∘C 250∘C 350∘C and 450∘C The resultsdemonstrated that the thermal stability of glass-based PC-WLEDs outperformed the silicone-based PC-WLEDs Thenovel development of glass-based PC-WLEDs is essentiallycritical to the application of LED modules in the area whereabsolute reliability is required and where silicone simplycannot stand the heat humidity or other deteriorating factors

due to its low thermal stability The multiphosphors layer ofglass as an encapsulating material may be advanced for manyapplications where the LEDmodules with high reliability arerequired

2 Experiment and Measurement

The glass matrix was composed of SiO2 Na2CO3 Al2O3

and CaO to be mixed and then melt at 1300∘C for 1 hourin a platinum crucible The cooled cullet glass (SiO

2-Na2O-

Al2O3-CaO) was milled into powders and kept dried Yellow

(Y3Al5O12Ce3+ YAG based) green (Lu

3Al5O12Ce3+ LuAG

based) and red (CaAlSiN3Eu2+ nitride based) phosphors of

different ratio were uniformly mixed into the matrix glasspowder followed by melting at 680∘C for 6 hours labeledas Y1G0R0DG Y

1G1R1DG Y

2G1R1DG Y

1G2R1DG and

Y1G1R2DG according to the composition ratio among yel-

lowgreenred phosphor in the glass phosphors These glassphosphor samples were then polished to 05mm of thicknessafter quenching down to room temperature With 15mmin diameter and 05mm thick the solidified glass phosphorcircular disks were entirely covered over the LED and thereflective cup to form a WLED module An integratingsphere equipped with an optical fiber and a CCD detectorwas employed to measure the optical spectra of the WLEDmodule

For thermal aging tests (its setup as shown in Figure 1)eleven phosphor disk samples from low-temperature glassCeYDG were aging at 150∘C 250∘C 350∘C and 450∘Cfor 1008 hours All the samples of MPDG (Y

1G1R1DG)

with diameter thickness and chromaticity coordinates were15mm (plusmn025) 05mm (plusmn0025) and (036 plusmn 0005 029 plusmn0005) as shown in Table 1

Thermal aging tests were measured periodically in orderto characterize the degradation of phosphor materials onlumen CIE and CRI The data of all samples were obtainedthrough the LED-645 test system (Lightports) The quantumyield (QY) is one of the major parameters used as a selected

International Journal of Photoenergy 3

Table 1 High CRI sample counts of accelerated test

Aging temperature (∘C) 150 250 350 450Sample quantity (pcs) 11 11 11 11Chromaticity coordinates (035 028) (035 028) (035 028) (035 028)Diameter (mm) 15 15 15 15Thickness (mm) 05 05 05 05

0

5

10

15

20

Qua

ntum

yie

ld d

ecay

()

Aging time (hrs)

150∘C (MPDG)

250∘C (MPDG)

350∘C (MPDG)

450∘C (MPDG)

150∘C (MPDS)

250∘C (MPDS)

0 250 500 750 1000

Figure 2 Quantum yield decay () versus aging time for PC-WLEDs of MPDG and MPDS samples at different temperatures

criterion of luminescence materials in solid-state lightingapplications as shown in the following

QY =119873erm119873Abs (1)

where the QY of the wavelength converting materials isdefined as the ratio of the number of photons emitted (119873erm)to the number of photons absorbed from the emission of thepumping light sources (119873Abs) where the number of photonsin each wavelength119873(120582) (cpsnm) can be obtained throughdividing spectrum distribution 119875(120582) (mWnm) by photonenergy ℎ] (J) [19]

CRI remanence is defined as the measured value of CRIafter thermal degradation

The chromaticity shift is defined as

Δ119864 = radic(1199061015840119891minus 1199061015840119894)2

+ (V1015840119891minus V1015840119894)2

+ (1199081015840119891minus 1199081015840119894)2

(2)

where 1199061015840 = 4119909(3 minus 2119909 + 12119910) V1015840 = 9119910(3 minus 2119909 + 12119910) and1199081015840 = 1 minus 1199061015840 minus V1015840 The 1199061015840 and V1015840 are the uniform chromaticitycoordinates [20] the119909 and119910 are the chromaticity coordinates(CIE 1931) and the 119894 and 119891 are the chromaticity shift beforeand after test respectively A schematic diagram of the testchamber for optical measurements is shown in Figure 2The test chamber consisted of a 5W GaN blue-light LEDa heat sink a removable phosphor layer and an integral

0

20

40

60

80

100

CRI r

eman

ance

Aging time (hrs)

150∘C (MPDG)

250∘C (MPDG)

350∘C (MPDG)

450∘C (MPDG)

150∘C (MPDS)

250∘C (MPDS)

0 250 500 750 1000

Figure 3 The CRI remanence versus aging time for PC-WLEDs ofMPDG and MPDS samples at different temperatures

sphere LED and phosphor layer were integrated togetherThis setup is to ensure the thermal aging effect on phosphorlayer after thermal aging tests that can be obtained preciselyLumen degradation chromaticity shift and CRI loss at thewavelength of 460 nm were recorded and compared beforeand after each thermal test

3 Results and Discussion

Table 2 shows optical properties of the WLEDs utilizingMPDG The color coordinates and color temperature of theWLED utilizing Y1G1R1DG are (0358 0288 3923K) withhigh color rendering index up to 85 suitable for interiorlighting

31 Thermal Stability of High CRI Glass Phosphors Thethermal stability test results of both types of samples werecarried out at 150∘C 250∘C 350∘C and 450∘C for 1008 hoursDue to silicone material carbonized above 280∘C MPDSsamples can merely be characterized under this temperatureThus MPDS can only be compared with MPDG below suchcritical temperature while the characteristics of MPDG willbe still presented at 350∘C and 450∘C

311 Quantum Yield Decay To investigate the reliability ofthe high CRI phosphor with the glass and silicone QY decaywas measured as a function of aging time after thermal aging


Table 2 Optical properties of MPDG based WLED

MPDG type Top view CIE (x y) CCT (K) CRI QY ()

Y1G0R0DG (0321 0325) 6043 6858 6836

Y1G1R1DG (0358 0288) 3923 8525 5557

Y2G1R1DG (0405 0363) 3248 7396 5940

Y1G2R1DG (0375 0334) 3803 8125 5531

Y1G1R2DG (0428 0302) 2182 7016 4724

Table 3 Characteristics of MPDG and MPDS based WLED samples accelerated thermal aging after 1008 hours

Characteristics Phosphor layer type 150∘C 250∘C 350∘C 450∘C

QY decay () MPDG 12 17 2 22MPDS 37 179 NA NA

CRI remanence MPDG 100 100 100 100MPDS 982 834 NA NA

CIE shift (10minus3) MPDG 35 42 46 55MPDS 101 1518 NA NA

at 150 and 250∘C for MPDG and MPDS shown in Figure 2at measurement period 250 hours After 1080-hour agingthe QY losses of MPDG were 12 17 2 and 22 at150∘C 250∘C 350∘C and 450∘C respectively The QY lossesof MPDS were 37 and 179 times higher thanMPDG at 150∘Cand 250∘C respectively MPDG samples maintained goodthermal stability in QY characteristic

312 Color Rendering Index Remanence CRI remanence wasmeasured as a function of aging time of the MPDG andMPDS after thermal aging at 150∘C 250∘C 350∘C and 450∘Cat measurement period 250 hours shown in Figure 3 After250-hour aging the CRI remanence of MPDS was 982 and834 at 150∘C and 250∘C respectively while CRI attenuationwas almost undetectable in the case ofMPDG indicating that


0

50

100

150

200

CIE

shift

(ΔE

) (10minus3)

Aging time (hrs)

150∘C (MPDG)

250∘C (MPDG)

350∘C (MPDG)

450∘C (MPDG)

150∘C (MPDS)

250∘C (MPDS)

0 250 500 750 1000

Figure 4 Chromaticity shift versus aging time for PC-WLEDs ofMPDG and MPDS samples at different temperatures

theMPDG samplesmaintained good thermal stability in CRIcharacteristic

313 Chromaticity Shift The chromaticity shift was mea-sured as a function of aging time of the MPDG and MPDSafter thermal aging at 150∘C 250∘C 350∘C and 450∘C asshown in Figure 4 for period of 1080 hours The chromaticityshifts of MPDG were 32 42 46 and 55 all in the order of10minus3 at 150∘C 250∘C 350∘C and 450∘C respectively After1008 hrs aging test the chromaticity shifts of MPDS were101 times 10minus3 and 1518 times 10minus3 at 150∘C and 250∘C respectivelyThe chromaticity of MPDG samples was thermally stablethan MPDSrsquos

314 Emission Spectrum The emission spectrum was mea-sured with integrating sphere spectrometer as a functionof aging time for the MPDG and MPDS after thermal agedat 150∘C 250∘C 350∘C and 450∘C (a) and (b) respectivelyshown in Figure 5 After industrial test standard 1008-hour aging better than MPDSrsquos all 4 samples of MPDGdid not have significant intensity decay as 2 and 3 at150∘C and 250∘C respectively less than 7 and 35 ofMPDS respectively This indicates that the MPDG samplemaintained good thermal stability regarding spectrum

In Table 3 for both MPDG and MPDS the acceleratedthermal aging test results of QY loss CRI remanence andCIE shift were summarized as regarding aging temperatureat 150∘C 250∘C 350∘C and 450∘C Due to a higher 119879

119892of

glass matrix it is also expected that internal strain is lessin glass materials than in silicone under similar thermalstress owing to glassrsquos lower thermal expansion coefficientSince silicone matrix material tends to be carbonized byhigher temperature aging [18] its thermal induced opticalcharacteristic deterioration such as CRI dropping and soforth will be prominent These results showed that MPDG

0

500

1000

1500

2000

2500

3000

3500

NonagingAging-150Aging-250

Aging-350Aging-450

Inte

nsity

(au

)

Wavelength (nm)

600

1500

400 450 500 550 600 650 700 750

(a) MPDG

0

500

1000

1500

2000

2500

3000

3500

Inte

nsity

(au

)


Wavelength (nm)400 450 500 550 600 650 700 750

(b) MPDS

Figure 5 Emission spectrum versus aging time for PC-WLEDs ofMPDG and MPDS samples at different temperatures

phosphor conversion layer is effective for long-time high-temperature operation and high CRI potentially for use inhighly efficient and high output power LEDs

4 Conclusion

The highly thermal stable phosphor-doped glass materialhas been successfully developed with both higher CRI andQY than those made of silicone CRI remanence and CIEshift in glass-based high-power PC-WLEDs outperformedsilicone base under thermal aging at 150 250 350 and 450∘Cfor industrial test standard 1008 hours The results showedthat the glass-based PC-WLEDs held better thermal stabilityin QY decay CRI remanence and chromaticity shift thanthe silicone-based PC-WLED due to higher glass transitiontemperature (119879

119892) of glass material property More thermally


stable phosphor layer of glass encapsulation material may bebeneficial for many applications where LED modules withhigh power and high reliability are demanded for the next-generation solid-state lighting industry

Conflict of Interests

The author declares that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work was supported by the Science Park Administra-tion under the Grant 102A10 the National Science Coun-cil under the Grants NSC 101-2218-E-269-001 NSC 101-2622-E-269-020-CC2 and NSC 101-3113-E-110-002-CC2 andthe Advanced Optoelectronic Technology Center NationalCheng Kung University Taiwan

References

[1] D A Steigerwald J C Bhat D Collins et al ldquoIlluminationwithsolid state lighting technologyrdquo IEEE Journal on Selected Topicsin Quantum Electronics vol 8 no 2 pp 310ndash320 2002

[2] J K Kim and E F Schubert ldquoTranscending the replacementparadigm of a solid-state lightingrdquo Optics Express vol 16 no26 pp 21835ndash21842 2008

[3] M R Krames O B Shchekin R Mueller-Mach et al ldquoStatusand future of high-power light-emitting diodes for solid-statelightingrdquo IEEEOSA Journal of Display Technology vol 3 no 2pp 160ndash175 2007

[4] S-R Lim D Kang O A Ogunseitan and J M SchoenungldquoPotential environmental impacts from the metals in incandes-cent compact fluorescent lamp (CFL) and light-emitting diode(LED) bulbsrdquo Environmental Science and Technology vol 47 no2 pp 1040ndash1047 2013

[5] J K Sheu S J Chang C H Kuo et al ldquoWhite-light emis-sion from near UV InGaN-GaN LED chip precoated withbluegreenred phosphorsrdquo IEEE Photonics Technology Lettersvol 15 no 1 pp 18ndash20 2003

[6] S Muthu F J P Schuurmans and M D Pashley ldquoRed greenand blue LEDs for white light illuminationrdquo IEEE Journal onSelected Topics inQuantumElectronics vol 8 no 2 pp 333ndash3382002

[7] K S Ramaiah Y K Su S J Chang and C H Chen ldquoAcomparative study of blue green and yellow light emitting diodestructures grown by metal organic chemical vapor depositionrdquoSolid-State Electronics vol 50 no 2 pp 119ndash124 2006

[8] J P You N T Tran and F G Shi ldquoLight extraction enhancedwhite light-emitting diodes with multi-layered phosphor con-figurationrdquo Optics Express vol 18 no 5 pp 5055ndash5060 2010

[9] R Mueller-Mach G O Mueller M R Krames and T TrottierldquoHigh-power phosphor-converted light-emitting diodes basedon III-nitridesrdquo IEEE Journal on Selected Topics in QuantumElectronics vol 8 no 2 pp 339ndash345 2002

[10] J Zhang and N Tansu ldquoImprovement in spontaneous emissionrates for InGaN quantum wells on ternary InGaN substrate forlight-emitting diodesrdquo Journal of Applied Physics vol 110 no 11Article ID 113110 2011

[11] H Zhao G Liu J Zhang J D Poplawsky V Dierolf and NTansu ldquoApproaches for high internal quantum efficiency greenInGaN light-emitting diodes with large overlap quantumwellsrdquoOptics Express vol 19 no 14 pp A991ndashA1007 2011

[12] E Rangel E Matioli Y-S Choi C Weisbuch J S Speck andE L Hu ldquoDirectionality control through selective excitation oflow-order guided modes in thin-film InGaN photonic crystallight-emitting diodesrdquo Applied Physics Letters vol 98 no 8Article ID 081104 2011

[13] Y-K Ee P Kumnorkaew R A Arif H Tong J F Gilchrist andN Tansu ldquoLight extraction efficiency enhancement of InGaNquantumwells light-emitting diodes with polydimethylsiloxaneconcave microstructuresrdquo Optics Express vol 17 no 16 pp13747ndash13757 2009

[14] R-J Xie N Hirosaki N Kimura K Sakuma and M Mit-omo ldquo2-phosphor-converted white light-emitting diodes usingoxynitridenitride phosphorsrdquo Applied Physics Letters vol 90no 19 Article ID 191101 2007

[15] S Nizamoglu G Zengin and H V Demir ldquoColor-convertingcombinations of nanocrystal emitters for warm-white lightgeneration with high color rendering indexrdquo Applied PhysicsLetters vol 92 no 3 Article ID 031102 2008

[16] C-C TsaiW-CCheng J-K Chang et al ldquoUltra-high thermal-stable glass phosphor layer for phosphor-converted white light-emitting diodesrdquo IEEEOSA Journal of Display Technology vol9 no 6 pp 427ndash432 2013

[17] H-C Kuo C-W Hung H-C Chen et al ldquoPatterned structureof remote phosphor for phosphor-converted white LEDsrdquoOptics Express vol 19 no 14 pp A930ndashA936 2011

[18] INTEMATIX Report ChromaLit Remote Phosphor for Down-light Applications 2013

[19] S Fujita A Sakamoto and S Tanabe ldquoLuminescence charac-teristics of YAG glass-ceramic phosphor for white LEDrdquo IEEEJournal on Selected Topics in Quantum Electronics vol 14 no 5pp 1387ndash1391 2008

[20] J-S Wang C-C Tsai J-S Liou et al ldquoMean-time-to-failureevaluations of encapsulation materials for LED package inaccelerated thermal testsrdquo Microelectronics Reliability vol 52no 5 pp 813ndash817 2012

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal of


Journal of

Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


Computer system Glass phosphor

Integrating sphere

Sensor

Fiber sensor

LED tester LED-645

20W blue LED

Figure 1 The test chamber schematic for optical measurement

index (CRI) of theWLEDs is usually less than 70 which is notacceptable for general interior illumination and some speciallighting including medical applications and architecturallighting To achieve high color rendering properties multi-phosphors such as redyellow and orangeyellow have to beadded into the color conversion layer Multiphosphor-dopedsilicone as the color conversion layer of the high-CRI WLEDhas been fabricated to demonstrate the above purpose [14 15]but the poor thermal stability of the silicone matrix weakensthe superiority for high-luminance lighting applications dueto the lower glass transition temperature of silicone (150∘C)In the previous works for yellow light emission to mix withblue light from LED we have demonstrated novel glass-basedphosphorswith excellent thermal stability for the applicationsof high-power WLEDs [16] but the resulted CRI values werenormally as low as 70s with single phosphor powder

Remote phosphor was studied as an alternative technol-ogy for white light LED Kuo et al investigated patternedstructure of remote phosphor for phosphor-converted whitelight LEDs [17] This patterned structure was designed toreduce the angular-dependent correlated color temperature(CCT) Intematix Company reported polycarbonate-basedremote phosphor layer around source LED [18] though glass-based remote phosphor product could be under develop-ment

In this study we fabricated a thermally stable multi-phosphor-doped glass (MPDG) for the goal The resultsshowed that the glass-based PC-WLEDs exhibited goodthermal stability in lumen loss chromaticity shift CRI andQE characteristics Then we compared with the silicone-based high-power PC-WLEDs under thermal aging at lowertemperature of 150∘C 250∘C 350∘C and 450∘C The resultsdemonstrated that the thermal stability of glass-based PC-WLEDs outperformed the silicone-based PC-WLEDs Thenovel development of glass-based PC-WLEDs is essentiallycritical to the application of LED modules in the area whereabsolute reliability is required and where silicone simplycannot stand the heat humidity or other deteriorating factors

due to its low thermal stability The multiphosphors layer ofglass as an encapsulating material may be advanced for manyapplications where the LEDmodules with high reliability arerequired

2 Experiment and Measurement

The glass matrix was composed of SiO2 Na2CO3 Al2O3

and CaO to be mixed and then melt at 1300∘C for 1 hourin a platinum crucible The cooled cullet glass (SiO

2-Na2O-

Al2O3-CaO) was milled into powders and kept dried Yellow

(Y3Al5O12Ce3+ YAG based) green (Lu

3Al5O12Ce3+ LuAG

based) and red (CaAlSiN3Eu2+ nitride based) phosphors of

different ratio were uniformly mixed into the matrix glasspowder followed by melting at 680∘C for 6 hours labeledas Y1G0R0DG Y

1G1R1DG Y

2G1R1DG Y

1G2R1DG and

Y1G1R2DG according to the composition ratio among yel-

lowgreenred phosphor in the glass phosphors These glassphosphor samples were then polished to 05mm of thicknessafter quenching down to room temperature With 15mmin diameter and 05mm thick the solidified glass phosphorcircular disks were entirely covered over the LED and thereflective cup to form a WLED module An integratingsphere equipped with an optical fiber and a CCD detectorwas employed to measure the optical spectra of the WLEDmodule

For thermal aging tests (its setup as shown in Figure 1)eleven phosphor disk samples from low-temperature glassCeYDG were aging at 150∘C 250∘C 350∘C and 450∘Cfor 1008 hours All the samples of MPDG (Y

1G1R1DG)

with diameter thickness and chromaticity coordinates were15mm (plusmn025) 05mm (plusmn0025) and (036 plusmn 0005 029 plusmn0005) as shown in Table 1

Thermal aging tests were measured periodically in orderto characterize the degradation of phosphor materials onlumen CIE and CRI The data of all samples were obtainedthrough the LED-645 test system (Lightports) The quantumyield (QY) is one of the major parameters used as a selected




0

5

10

15

20

Qua

ntum

yie

ld d

ecay

()

Aging time (hrs)

150∘C (MPDG)

250∘C (MPDG)

350∘C (MPDG)

450∘C (MPDG)

150∘C (MPDS)

250∘C (MPDS)

0 250 500 750 1000



QY =119873erm119873Abs (1)




Δ119864 = radic(1199061015840119891minus 1199061015840119894)2

+ (V1015840119891minus V1015840119894)2

+ (1199081015840119891minus 1199081015840119894)2

(2)


0

20

40

60

80

100

CRI r

eman

ance

Aging time (hrs)

150∘C (MPDG)

250∘C (MPDG)

350∘C (MPDG)

450∘C (MPDG)

150∘C (MPDS)

250∘C (MPDS)

0 250 500 750 1000










Y1G0R0DG (0321 0325) 6043 6858 6836

Y1G1R1DG (0358 0288) 3923 8525 5557

Y2G1R1DG (0405 0363) 3248 7396 5940

Y1G2R1DG (0375 0334) 3803 8125 5531

Y1G1R2DG (0428 0302) 2182 7016 4724









0

50

100

150

200

CIE

shift

(ΔE

) (10minus3)

Aging time (hrs)

150∘C (MPDG)

250∘C (MPDG)

350∘C (MPDG)

450∘C (MPDG)

150∘C (MPDS)

250∘C (MPDS)

0 250 500 750 1000






119892of


0

500

1000

1500

2000

2500

3000

3500


Aging-350Aging-450

Inte

nsity

(au

)

Wavelength (nm)

600

1500

400 450 500 550 600 650 700 750

(a) MPDG

0

500

1000

1500

2000

2500

3000

3500

Inte

nsity

(au

)


Wavelength (nm)400 450 500 550 600 650 700 750

(b) MPDS



4 Conclusion







Acknowledgments


References






























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




0

5

10

15

20

Qua

ntum

yie

ld d

ecay

()

Aging time (hrs)

150∘C (MPDG)

250∘C (MPDG)

350∘C (MPDG)

450∘C (MPDG)

150∘C (MPDS)

250∘C (MPDS)

0 250 500 750 1000



QY =119873erm119873Abs (1)




Δ119864 = radic(1199061015840119891minus 1199061015840119894)2

+ (V1015840119891minus V1015840119894)2

+ (1199081015840119891minus 1199081015840119894)2

(2)


0

20

40

60

80

100

CRI r

eman

ance

Aging time (hrs)

150∘C (MPDG)

250∘C (MPDG)

350∘C (MPDG)

450∘C (MPDG)

150∘C (MPDS)

250∘C (MPDS)

0 250 500 750 1000










Y1G0R0DG (0321 0325) 6043 6858 6836

Y1G1R1DG (0358 0288) 3923 8525 5557

Y2G1R1DG (0405 0363) 3248 7396 5940

Y1G2R1DG (0375 0334) 3803 8125 5531

Y1G1R2DG (0428 0302) 2182 7016 4724









0

50

100

150

200

CIE

shift

(ΔE

) (10minus3)

Aging time (hrs)

150∘C (MPDG)

250∘C (MPDG)

350∘C (MPDG)

450∘C (MPDG)

150∘C (MPDS)

250∘C (MPDS)

0 250 500 750 1000






119892of


0

500

1000

1500

2000

2500

3000

3500


Aging-350Aging-450

Inte

nsity

(au

)

Wavelength (nm)

600

1500

400 450 500 550 600 650 700 750

(a) MPDG

0

500

1000

1500

2000

2500

3000

3500

Inte

nsity

(au

)


Wavelength (nm)400 450 500 550 600 650 700 750

(b) MPDS



4 Conclusion







Acknowledgments


References






























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




Y1G0R0DG (0321 0325) 6043 6858 6836

Y1G1R1DG (0358 0288) 3923 8525 5557

Y2G1R1DG (0405 0363) 3248 7396 5940

Y1G2R1DG (0375 0334) 3803 8125 5531

Y1G1R2DG (0428 0302) 2182 7016 4724









0

50

100

150

200

CIE

shift

(ΔE

) (10minus3)

Aging time (hrs)

150∘C (MPDG)

250∘C (MPDG)

350∘C (MPDG)

450∘C (MPDG)

150∘C (MPDS)

250∘C (MPDS)

0 250 500 750 1000






119892of


0

500

1000

1500

2000

2500

3000

3500


Aging-350Aging-450

Inte

nsity

(au

)

Wavelength (nm)

600

1500

400 450 500 550 600 650 700 750

(a) MPDG

0

500

1000

1500

2000

2500

3000

3500

Inte

nsity

(au

)


Wavelength (nm)400 450 500 550 600 650 700 750

(b) MPDS



4 Conclusion







Acknowledgments


References






























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0

50

100

150

200

CIE

shift

(ΔE

) (10minus3)

Aging time (hrs)

150∘C (MPDG)

250∘C (MPDG)

350∘C (MPDG)

450∘C (MPDG)

150∘C (MPDS)

250∘C (MPDS)

0 250 500 750 1000






119892of


0

500

1000

1500

2000

2500

3000

3500


Aging-350Aging-450

Inte

nsity

(au

)

Wavelength (nm)

600

1500

400 450 500 550 600 650 700 750

(a) MPDG

0

500

1000

1500

2000

2500

3000

3500

Inte

nsity

(au

)


Wavelength (nm)400 450 500 550 600 650 700 750

(b) MPDS



4 Conclusion







Acknowledgments


References






























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





Acknowledgments


References






























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

Research Article Color Rendering Index Thermal Stability...

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