Solid StateCommunications,Vol. 23,pp. 193—195,1977. PergamonPress. Printedin GreatBritain

DECAYMODESOF THE3000A EMISSIONBAND IN KC1 : Tl~

S. Aiello, S. BenciandM. Manfredi

Istituto di Fisica,UniversitI di Parma,Parma,Italyand

GruppoNazionaledi StrutturadellaMateria,CNR, Italy

(Received21 February 1977by R.Fieschi)

The time behaviorof the 3000A luminescencesignalsof KG:Ti ciystalsis complex.Threedifferentcomponentscanberesolvedin the temperaturerangeinvestigated(80—340K). Theseresultsthatare typicalfor theA~emissionof phosphorslike KI : fl4 andKG:Pb24,cannotbe explainedwith the availabletheoreticalmodelsforKG : Ti system.

PREVIOUSlifetime measurementsof theA~emission accuracythestudyof the shapeof theluminescencein systemslike KI : TI4 [1] , Na!:Tl4~[2] andKG: P’o24 signalof the 3050emissionin KC1 : W. Ourpurposeis[3] evidentiatedthe existenceof threecomponentsin to understandtheorigin andthe natureof the thirdthe decayspectra.Two of thesecomponentscan be componentof lifetime found in the otherphosphors.explainedconsideringtheradiativetransitionsfrom the The experimentalapparatususedhasbeenpreviouslyJahn—Tellerminimaon 3T

1~and3A

114 APESto the described[1]. ThemeasuredTl4 concentrationsranged

groundstate.The minimaon the 3A1~APESshouldbe between6 x l0’

6/cc and6 x 10’7/cc.For selectingtheresponsiblefor the componentwith lifetime dependent excitationandemissionlight bothinterferencefilterson the temperature,while theminima on the3T

1~ andmonochromatorhavebeenused.WehavestudiedAPESshouldbe responsiblefor thecomponentwith the theluminescencesignalsfiltering boththe light emittedfastestlifetime. The third componentis not completely atabout3200A (right partof the emissionband)andunderstood;sometentativeexplanationsinvoke tunneling thelight emittedatabout3000A (left partof theprocessesbetweennot equivalentminima, suchastunnel- emissionband).The luminescencesignalshavebeening from the minimaresponsiblefor theAT emissionto obtainedexcitingthesamplesin theA (2450A), BtheA~minima(K! andNa!) or tunnelingbetweenthe (2100A) andC(1950A)absorptionbands.Thesameminima shiftedin energyby thepresenceof thevacancy behaviourwith the temperaturefor lifetimesandrelative(KG:Pb

2~). intensitieshasbeenobservedforexcitationin all theMost emissionresultson KG: Ti4 crystalswith low threeabsorptionbands.The resultswewill discussin

concentrationof impuritieshavenot evidentiatedtwo the following refer to the datatakenwith excitationindistinct emissionbandsafterA light excitation,con- theA band,andare representedin thefigures.nectedwith two groupsof not equivalentminima on the The decaysignals(at3200A andalsoat3000A)3T

1,,, APES.Theseresultshaveatheoreticalsupportin show a complexshapewith threecomponentseachonetheanalysisof Kristofel [4] andFukuda[5] , who characterizedby adifferentlifetime.The lifetime offoundthatoneof thesupposedminimaon the

3T~ the componentcalledr3 is stronglytemperature

APESis a saddlepoint. dependentwhile thelifetime of theother two corn-Measurementsof Gebhardtandco-workers[6] ponents(calledTi andr2) is practicallyconstantin the

confirmthattheminima on3T

11,APESareequivalent, temperaturerangewherethey arepresent.only slightly shiftedin the Q2Q~spacewith respectto Figure 1 showsthe temperaturedependenceof the3A

1~APESminima.In thelight of theseinformations lifetime of the r3 componentin therange 80—340K.onecanexpectfor the 3050A emissionin KG: Ti

4 The behaviourof theintensityof thiscomponentwithcrystalsadecaysignalwith two components,as measured the temperatureis the samealreadymeasuredby otherby Lllingworth [7] andTomuraeta!. [8]. authors[8].

EdgertonandTeegarden[9] , howeverevidentiated The componentr~showsalifetime of about30nsecthatthe dependencefrom thetemperatureof the peak andthebehaviourof theintensityI~of thiscomponentpositionandthe shapeof the 3050emissionbandcan is shownin Fig. 2. Thiscomponentis no longer detect-indicatethat two emissionscouldbeinvolved, able for temperatureshigherthan200K. At about200K

We haveundertakenwith betterresolutionand athird component(T2) startsto appearandits intensity

193

194 DECAY MODES OF THE 3000A EMISSIONBAND IN KG : TI4 Vol. 23,No.3

3

2 ~.

12E

Vci — .•~ 16

0-Vv .

V

V LU 0 I I— 220 300 380-i VV

2 V Temperature (oK)V V

V V ~

3 Fig.3. Behaviourof the intensity12 of the r2 corn-

10 I I ~ V ponentasafunction of the temperature.60 140 220 300

Temperature (‘K) consideringthe transitionsfrom theminima on3Ti~

and3A iu APESto theground staterespectively.TheFig. 1. Behaviourof the T

3 lifetime with thetemperature componentT2, thaton thelight of the theoreticalin therange80—340K. modelsup tonow developedfor KG : W crystalscan-

not beexplained,is a surprisingresultandseemstoimposesomenewtheoreticalinvestigationson thelevelschemafrom which theA emissiontakesplace.‘2

In fact our resultscanbeexplainedif we supposeIiinterestedin theA emissiona newenergylevel (differentfrom

3T~and3A~,,APES)from which thetransitionE

with r2 time constanttakesplaceor if we supposethat

• • • alsoin this caseon the3Ti~APES theminima arenot

~ 1.6 - . equivalent.0-~ U Observingtheresultsof Fig. 2 we cannotice that

the disappearanceof theT1 componentis connected

I I with the risingof the intermediatecomponentT2, asif60 140 220 the depopulationof theminima of ~Tj~APES(that is

theminima with the shortestlifetime)correspondstoTemperature (‘K)thepopulationof anotherlevel with differentlifetime.

Fig. 2. Behaviourof the intensityI~of the ri corn- Finally the resultsof lifetime andof emissionponentas a functionof the temperature. intensityof the differentcomponentsvs temperature

point out that the levelschemaof the excitedrelaxedversustemperatureis representedin Fig. 3;the lifetime statesof KC1 : Ti

1’ crystalsis like to that of KCI : Pb2~of the T

2 componentis temperatureindependentand its crystals,ratherthan to thatof TI dopedNal andKIvalueis 300 nsec. crystals.

The samelifetime valuesandthesametemperaturebehaviourfor the intensitieshavebeenobservedat3200andat 3000A, howeverthe T3 componentismore Acknowledgements— Someof theusedcrystalshaveintense,with respectto thecomponentswith shorter beenkindly furnishedby A. Ranfagniandco-workerslifetime, at 3200A than at 3000A. of theIROE—CNR,Firenze,Italy. Thetechnicalassist-

Thetwo componentsri and73 are explained anceof Mr. R Valentiis greatlyappreciated.

REFERENCES

BENCI S., FONTANA M.P. & MANFREDI M., Solid StateCommun. 18, 1423(1976).

2. BENCI S., FONTANA M.P. & MANFREDI M., Phys.StatusSolidi(in press).

3. BENCI S., CAPELLETfl R., FERMI F. & MANFREDI M., SecondEurophysicalTopical ConferenceonLatticeDefectsin Ionic Crystals.Berlin (1976);J. dePhys. (in press).

4. KRISTOFELN., Opt. Spectr.9, 324(1960).

Vol. 23,No.3 DECAY MODES OF THE 3000A EMISSIONBAND IN KG :W 195

5. FUKUDA A.,Thys.Rev.BI,416l (1970).

6. GERHARDT V. & GEBHARDT W,Thys.StatusSolidi(b) 59, 187 (1973).

7. ILLINGWORTH R.,Thys.Rev. 136A, 508(1964).

8. TOMURAM.&NISHIMURAH.,J. Phys.Soc.Japan20,1536(1965).

9. EDGERTON R. & TEEGARDEN K.,Thys.Rev. 169,129(1962).