白光led与荧光粉之特性探讨Properties of white light LED and phosphors.docx
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白光led与荧光粉之特性探讨Properties of white light LED and phosphors.docx
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白光led与荧光粉之特性探讨PropertiesofwhitelightLEDandphosphors
白光led与荧光粉之特性探讨(PropertiesofwhitelightLEDandphosphors)
PropertiesofwhitelightLEDandphosphors
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Lighting(Lighting)anddisplay(Display)isthetwomostphotovoltaicindustryisanimportantareaofdevelopment,whiletheglobalfossilenergyexhaustionandenvironmentalpollutionhavebecomeincreasinglyserious,whiteLEDcanalsomeetthedoublecharacteristicof"energysaving"and"environmentalprotection"(LightEmittingDiode),thelightinganddisplayapplicationsthedevice,inrecentyearsattractedmuchattentionandhighpriority.
WhiteLEDbecauseofhavingthecharacteristicsofbothenergysavingandenvironmentalprotection,generallywillbearevolutionarylightsourcetoreplacethehotlampandfluorescentlamp;andthefluorescentmaterialsarethekeymaterialsoflightinganddisplaydevice,especiallysincetherapiddevelopmentofhighbrightnessLED,andagainattractedmuchattention.ThewhiteLEDhasmadeanumberoffeasibleways,whichmadebyfluorescentpowderforwhiteLED,hastheadvantagesofsimplemanufacture,lowcostandeasydrivingetc,onthefutureoflightinganddisplayapplications,whichwillplayanimportantrole.
Atpresent,therearethreewaystomakemorecommonwhiteLED,thefirstoneisthered,greenandbluecolor,dolightmixingsecondkinds;istheuseofultravioletLEDlightandfluorescentpowderbyred,greenandblue,andmixedwhitelight;thethirdistousetheblueonyellowphosphor.Mixedwhitelight.TheuseofmultiplecurrentphosphidehighbrightnessLEDmajority(suchasInGaAlP)ornitride(InGaN)semiconductormaterialsproducedbythelightcolorduetotheluminescencemechanismandmaterialgapconstraints,thereforetheyallbelongtothenarrowwidthofthemonochromaticlight.Asforlightinganddisplayapplications,mostofthemneedtousewhitelightsource.IfweuseLEDtomakewhitelightsource,wemustapplythetechnologyofcombinationoflightandcolortoachievethepurposeofobtainingwhitelight.AtpresentallkindsoffeasibletechnologyportfoliointhecolorofwhiteLED,usingsinglechipLED(Single-chipLED)combinedwithvarioustypesoffluorescentmaterialtochangecolorandlightmixingeffect,itisoneofthemostconvenientandmostcost-effectiveway,andtheapplicationofinorganicphosphor(Phosphor)whiteLEDproduced.GeneralalsocalledPC-White-LED(Phosphor-convertedwhite-LED).
LED(Blue-LED+Yellowphosphor),adocumentpointedoutthatthecurrentradiationsuchwhiteLEDspectra,bluebandpartsaccountedforabout31%andthetotalwhitelight,theyellowlightphosphorwhitelightoccupiesaproportionof69%ofthetotal.
Ontheotherhand,ifthewhiteLEDfluorescentpowderproducedwithUV-LED(UV-LED+R/G/Bphosphors),UV-LEDfromUVallthroughthephosphorconversionisformedbyvisiblelight,solightphosphor,almostwhitelight100%.totalaccordingtotheaboveanalysis,wecanclearlyunderstandtheimportanceandstatusthefluorescentpowderwhichholdsinthesinglechipwhiteLED.
WhitelightLED
WhiteLEDistheearliestintheblueLEDcollocation"YAG"(YAG:
Ce3+YttriumAluminumGarnetdopedwithCe3+;activator)ofyellowfluorescentpowdermadefromsuchwhiteLEDlaunchattractedglobalattention,
AneweraofLEDapplicationshasalsobegun.Infact,inadditiontothewhiteLEDblueLEDandyellowfluorescentpowdermakingwayoutside,stillcanaddgreen/blueLEDredfluorescentpowderorothercombinations,orbyUV-LEDplusblue/Green/redfluorescentpowderorothercombinationsmade.
ItalsocanbedirectlyappliedtoanumberofdifferentcolorLEDchipmadeofmonomer(Single-chip)whiteLED,orisadirectapplicationofanumberofdifferentcolorcombinationsofLEDandwhiteLEDmodule(LEDmoduleorarray/array),althoughitsdrivingcircuitisrelativelycomplex,relativelyhighcost,butinthedisplaybacklight.Intermsofperformance,canobtaingoodcolorsaturationorcolorgamutcharacteristicsof[7],andthewhiteLEDwithfluorescentpowder,withdifferentconsiderationsinapplication.
ThefluorescentpowderintheLEDapplication,inadditiontothewhiteLED,forasingleLEDchipcan'tobtaincolorsuchasredandpurple"isnotsaturatedlightandcolorgamutrangeofcolor,orasingleLEDchiplightemittingefficiencyispoorcolorsuchasgreen,yellowlightpart(about520~590partofnmbandoflightcolor)andhaveapplicationvalue.Asforlightemittingdiodesmadewithphosphors,possibleapplicationsincludelighting,backlight,andinstructions/decorations.AsforthewhiteLEDinlightinganddisplayimportantcharacteristicsofbacklightapplicationsthatneedtobeconsideredinclude:
luminousefficiency,servicelife,colortemperature,colorrenderingandcolor/colorsaturationcoefficient,theimportantcharacteristicsofthepresent,isalsoactivelydraftingorformulaterelevantspecificationsandtestingstandards.AsfortheimportantfeaturesandrequirementsofwhitelightLED,thefollowingaredescribedbelow.
1luminousefficiency
Luminousefficiencyisoneofthemostimportantcharacteristicsoflightsourceproducts.TheefficiencyofwhiteLEDoritsluminairesystemisusuallyillustratedbyluminousefficiency(Luminous,efficacy,Lumens,per,Watt,LPW,lm/W).
AccordingtotheUnitedStatesinSeptember2007announcedthesolidstatelightsourcelightingequipment"EnergyStar(ENERGYSTAR?
)",whichisaClassA(Near-termapplications),accordingtotherequirementsandapplicationofdifferentlightingequipment(suchasindoororoutdoor)provided,betweenthelightemittingefficiencybetween20~35LM/WandBrequirements(Future;performancetargets)fortheluminousefficiencyofnotlessthan70lm/W.
2.Servicelife
AtpresentmostoftheLED(Lumendepreciation)thenumberoflumenattenuationdegreetodefinelife,usuallychoosethenumberoflumensattenuationtotheoriginal50%or70%ofthetime(withL50orL70representative),asthelifeindexofLEDlightsource.FortheLEDmodule/array(Module/Array),thecurrentU.S.EnergyStarspecificationforindoorapplicationsofL70homefor25000hours,thehomeofL70foroutdoorapplicationsmorethan25000hours,andalltheL70commercialapplicationformorethan35000hours.AnotherliferelatedpropertyistheLED(Color)ofwhitelightmaintenance.TheenergystaroftheUnitedStatesiscurrentlyspecifiedduringtheaforementionedservicelife,
ChangesintheCIE1976chromaticitycoordinatesofallsolidstatelightsourceluminairemustbelessthan0.007.
3,colortemperature
Thecolortemperatureofblackbodyisbasedonheating,whenthetemperaturerisestoaboveacertainlevel,thelightcolorwillbegintograduallychange,whicharecorrespondingtothevariouscolortemperaturetotheabsolutetemperatureK(Kelvin)thatisthecolortemperature,colortemperaturecurvecommonlycalledPlanckcurve(Plankianlocus).
AsforthePlanckcurveinchromaticitycoordinate,usuallychoosecurveclosesttorepresentthecolortemperature,colortemperatureiscalledtheAssociation(Correlatedcolortemperature;CCT),iso-CCTlines(generalcanintersectwiththePlanckcurveofeachline)toassistintheidentification,theAmericanEnergyStarspecificationforallsolidstatelightsourcelightingequipment(Allluminaries),isthe2500K7000Ktemperaturerange,thechromaticitycoordinatesystem(suchasCIE1931)withinthecurvealongthePlanck,dividedinto2700K,3000K,and3500K,4000K,4500K,5000K,5700Kand6500Keightstandardcolortemperature(NominalCCT)theeightquadrilateralblocks(Quadrangles)asshowninfigure4-3-4,alsohasacleardefinitionforthecoordinatesofeachblockvertices,i.e.ifthecolorofwhiteLEDsolidlightsourcecoordinatesAllofthemneedtofallintotheeightquadrilateralblocks.AnotherfeaturerelatedtocolortemperatureisSpatialUniformity(Color),wherethechangesinCIE1976chromaticitycoordinatesfromdifferentanglesmustbelessthan0.004.
4,colorrenderingcoefficient
CRI(Colorrendition)isakindoflightsourcecanshowcolorfidelityabilitycharacteristicsofobjects,usuallyincolorcoefficient(Colorrenderingindex;CRI)astheindex,themeasurementstandardisthestandardlightsource(hotlamporD65standardlightsource)hasdefinedcolorilluminatedobjectsis100(100%truecolor),thepercentageofthetruedegreeofcolorinadditiontonumericaltestshowsthelightsourceobject(suchas75;75%truecolor),colorasthecoefficientsofthetestlightsource.Themeasurementandcalculationofthecolorcoefficient[13]isbasedonfourteenstandardcolorsamples(14,selected,Munsell,samples)toobtainthecolorvaluesofeachstandardcolor.TheenergystaroftheUnitedStatescurrentlydefinesthecolorrenderingas"allsolidstatelightsourcesforindooruse."thecolorfactoroftheluminaireshallnotbelessthan75(Note:
"CRI"and"Ra").
5colorgamut/colorsaturation
Colorreferstothecolordisplay,candisplaythecolornumber(todisplaycanbedisplayedontheCIEcolorcoordinatesystemontherangeofcolorsorfields)apracticalcharacteristicindex,alsoknownascolorsaturation.
Relativetotheimportanceofcolorrenderinginlightsources,thegamutisanimportantindicatorofthecolorcapabilityofthedisplay.Inessence,asinglewhiteLEDisunabletodiscussitsgamutpropertiesbecauseitalonedoesnothaveagamutofthischaracteristicindex.
However,whenwhitelightLEDapplicationsareusedasbacklightsourcesofdisplayssuchasTFT-LCD,
Throughthecolorfilterfilmwillbedecomposedintored/Green/blue(R/G/B)andotherprimarycolors,eachpixelthrough
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