[6]

Available online at www.sciencedirect.com

Journal of the European Ceramic Society 30 (2010) 17071715

Luminescent properties of rare earth (Er, Ybgar es

nnof Scd Techber 22010

Abstract

Yttrium alum stratenitrates. The posthermal ana t of tpacked nano tingup-conversio stigaup-conversion emissions arising due to 4S3/2 4I15/2 and 4F9/2 4I15/2 transitions, respectively for Er3+ ion were observed. Photoluminescenceand radiative life-times of the exited states of Er3+ in the visible and near IR ranges are also reported. 2010 Elsevier Ltd. All rights reserved.

Keywords: YAG; Solgel process; Films; Optical properties

1. Introdu

Yttriumused in numaterials aYAG demoductivity asYAG is dopemits lightcan conver

multiphotothe light haproperties oand concenand surface

The conmethod, bu

CorresponE-mail ad

0955-2219/$doi:10.1016/jction

aluminium garnet (YAG, Y3Al5O12) ceramics aremerous applications as structural and engineeringnd as host for solid state lasers and phosphors.19nstrates a high chemical stability, low electrical con-well as high resistance to creep.6,7,1012 Moreover,

ed with trivalent erbium (Er3+) and ytterbium (Yb3+)in UV, visible and IR spectrum. Also, Er3+ and Yb3+t photons from the infrared (IR) to the visible light byn absorption processes, which could be attractive forrvesting applications. The photoluminescence (PL)f phosphors strongly depend on the host lattice, typetration of activator ion,13 crystallite and particle size,morphology.14

ventional route to YAG is the solid state synthesist in order to achieve a large degree of homogeneity,

ding author. Tel.: +47 735 94084; fax: +47 735 91105.dress: [email protected] (T. Grande).

small particle size and thin film soft chemistry techniques aredesired. YAG and rare earth doped YAG thin films and powdershave been produced by various techniques, such as electrochem-ical synthesis,15 spray-inductively coupled plasma,16 plasmaspray process,17 pulsed laser deposition (PLD),18 solgel1921and metal-organic chemical vapour deposition (MOCVD).22 Inorder to achieve desirable properties of the thin films, precisecontrol of phase homogeneity, particle size and morphology isnecessary. Thus, the synthesis method is important for con-trolling the properties, the cost and possible applications ofthe films.4,6,16,21,22 Wu et al. reported film synthesis by thesolgel method using acetate and alkoxide precursors.20,21 Jiaet al. reported synthesis of thin films by Pechini solgel dip-coating method using citric acid and polyethylene glycol (PEG)as chelating and cross-linking agents, respectively.23

Lanthanide ions with luminescent properties are readilyincorporated in host materials as the f-electrons constituting thephotoactive center is well shielded.2426 However, in order tocontrol parasitic quenching mechanisms as well as introduc-ing more sophisticated photo-activity, some kind of organiccage or complex is needed, as shown e.g., for dendrimers,2729

see front matter 2010 Elsevier Ltd. All rights reserved..jeurceramsoc.2010.01.001net thin films and bulk samples synthtechnique

Edita Garskaite a, Mikael Lindgren b, Mari-Aa Department of Materials Science and Engineering, Norwegian University

b Department of Physics, Norwegian University of Science anReceived 22 June 2009; received in revised form 2 Decem

Available online 25 January

inium garnet (YAG) powders and thin films deposited on silicon subsolgel process resulted in an amorphous gel, and the thermal decom

lysis and X-ray diffraction. Powders were prepared by heat treatmen-crystalline particles were obtained on silicon substrates by dip-coan (anti-stoke emission) of Er, Yb co-doped YAG phosphors were inve) doped yttrium aluminiumised by an aqueous solgel

Einarsrud a, Tor Grande a,ience and Technology, 7491 Trondheim, Norwaynology, 7491 Trondheim, Norway009; accepted 4 January 2010

s were prepared by an aqueous solgel route using metalition and successive crystallization were characterized byhe amorphous gel, while crack-free thin films of denselytechnique. Photoluminescence (PL) properties as well asted. Green (555 nm) and red (650 nm) photoluminescence

1708 E. Garskaite et al. / Journal of the European Ceramic Society 30 (2010) 17071715

two-photonporphyrin pperformancmaterials corganometstate absorpwith high t

Aqueoutage that thlower comever, clustemoleculesquench lumthanides emHere we reppowders anusing yttriucomplexingMoreover,Fig. 1. Scheme of dip-coating sol, thin films, po

absorbing sensitized lanthanide complexes30 andhoto-chemistry.31,32 It was recently shown that high-e multi-functional hybrid organicinorganic hybridan be obtained by a solgel procedure; here an

allic platinum complex with strong triplet excitedtion was introduced into a laser hardened bulk matrix

emperature performance.33s based solgel methods have the additional advan-e environmental and health risks are considerably

pared to methods based on organic solvents. How-rs at high doping concentrations or water and similarwith vibration overtones in the NIR are known toinescence and shorten excited state life-times of lan-itting in this wavelength region, such as Er3+ ion.34ort the preparation of YAG and Er/Yb co-doped YAGd thin films by aqueous chemical solution depositionm and aluminium nitrates as precursors, acetic acid asagent and ethylene glycol as polymerization agent.

the luminescent properties of Er/Yb:YAG thin films

and bulk saEr/Yb dopcussed. It iobtained invia sequen

2. Experim

2.1. Synthe

A scheEr/Yb:YAGFig. 1. YttAldrich),98.5%, R(Er(NO3)3pentahydraused as cawas first dwder synthesis.

mples are also reported and the relationship betweening concentration and PL emission intensity is dis-s also demonstrated that the long excited life-timesthese systems can be used to harvest light at 980 nm

tial multiphoton absorption processes.

ental

sis of the sols, gels and powders

me for the synthesis route of the YAG andsols, gels, powders and thin films is presented in

rium nitrate hexahydrate (Y(NO3)36H2O, 99.9%,aluminium nitrate nonahydrate (Al(NO3)39H2O,iedel-de Haen), erbium nitrate pentahydrate5H2O, 99.9%, Aldrich) and ytterbium nitratete (Yb(NO3)35H2O, 99.999%, Aldrich) weretion precursors. Y(NO3)36H2O (7.66 g, 0.02 mol)issolved in 20 mL of CO2-free deionised water

E. Garskaite et al. / Journal of the European Ceramic Society 30 (2010) 17071715 1709

and a stochiometric amount of Al(NO3)39H2O (12.492 g,0.03 mol) dissolved in 20 mL of CO2-free deionised water wasadded. The60 mL ofyttriumalustirred forof ethylenemixture as1:1.75) andget a clear

A part oform transpfor 24 h andfurther ann30 C/h) foannealing t

PowdersY2.97Er0.02Er0.01Yb0.0Y2.4Er0.6Amolar ratioto EG correare labelled(1%), Y3AY3Al5O12:(20%) in thing rate 60calcined po200 C/h) f

2.2. Thin

The solto produceof 3% polMerckSchagent in orvolume ratiand Y/Al/Ewas 0.25 M

Pure anon as rece

Germany)nology, Co5 mm/min.single-dipplayer is cadip-coatingdeposited athe depositthen calcinheating ratannealed a3 h using 30at 600 C fosition the fiheating rate

2.3. Morphology and structure characterization

rmowi

rateis wr witlite sXRDM) o, and1 1),4 2)bro

opicy anltra

s deden

ed atanolets w(LVS

umin

e-reH 50nm

M).as u

stemon mNIR700 ncattewan

time(M

ratioing rbtai

s, reng thmea

sorptTho

we

alyz747

ults

rysta

calcalysiacetic acid (CH3COOH, glacial, Acros Organics;0.2 M) was added as complexing agent to theminium aqueous solution and the mixture was30 min at 6065 C. In the following step, 2 mLglycol (EG, 99%, Aldrich) was supplied to the

polymerisation agent (Y3+ to EG molar ratio wasthe final solution was further stirred for 30 min to

homogeneous precursor sol.f the YAl precursor sols was evaporated at 65 C toarent gels, which were further dried at 110115 Ccalcined at 600 C (heating rate 30 C/h) for 3 h and

ealed at 700, 750, 800, 850 and 900 C (heating rater 5 h in air with intermediate grinding between eachemperature.

with the compositions Y2.94Er0.03Yb0.03Al5O12,Yb0.01Al5O12, Y2.97Er0.015Yb0.015Al5O12, Y2.972Al5O12, Y2.85Er0.15Al5O12, Y2.7Er0.3Al5O12 andl5O12 were prepared by an optimised route using aof Me3+ (Y3+, Al3+, Er3+ and Yb3+) to acetic acid andsponding to 1:1.2 and 1:5, respectively. The samplesY3Al5O12:Er,Yb (1:1) (2%), Y3Al5O12:Er,Yb (2:1)

l5O12:Er,Yb (1:1) (1%), Y3Al5O12:Er,Yb (1:2) (1%),Er (5%), Y3Al5O12:Er (10%) and Y3Al5O12:Ere following. The gels were calcined at 600 C (heat-C/h) for 3 h. Isostatically compressed pellets of thewder were fired at 800 and 1200 C (heating rateor 5 h.

lms processing by dip-coating

s described in the previous paragraph were usedthin films by dip-coating. An aqueous solution

yvinyl alcohol (PVA, molecular weight = 72,000,uchardt) was added to the precursor sol as wettingder to improve the wettability of the substrate. Theo of the precursor sol and PVA solution was 1:1. Y/Alr/Yb ion concentration in the aqueous dip-coating sol.d Er/Yb-doped thin films of YAG were depositedived Si substrates (1 1 1), p-type (Crystal GmbH,using dip-coating technique (DC Mono, Nima Tech-ventry, UK) with an immersion and withdrawal rate ofFor pure YAG films, five layers were deposited by aing process. In a single dipping process the depositedlcined before a second layer is deposited by a new

step. For the ErYb doped YAG film 30 layers werelso by single-dipping method. Before annealing, alled films were dried at room temperature for 23 h,ed at 300 and at 350 C for 1 h, respectively withe of 30 C/h. After final deposition, the films weret 600 C for 1 h, at 800 C for 3 h and at 900 C forC/h heating rate. The deposited films were calcinedr 15 min with heating rate 300 C/h. After final depo-lms were annealed at 900 C for 1 h using 600 C/h.

Theformedheatinganalystometecrystaltion, d(FWH(6 4 0)the (2and (6mentalanisotrphologZeiss UIn-Len

Theanneal2-propof pellscope

2.4. L

Timan IBwith 1(5000lamp wThe sydetectimatsu9001block sing undecayscalingfor opeincludwere o

lengthscanni

Forton ablaser (spectraand an(type C

3. Res

3.1. C

TheTG angravimetrical analysis of the precursor gel was per-th a Netzsch STA 449C Jupiter in air using aof 10 C/min up to 800 C. X-ray diffraction (XRD)

as performed on a Bruker AXE D8 Focus diffrac-h a LynxEye detector using CuK radiation. Averageize of the films was estimated by the Scherrer equa-= K/ cos , using the full-width at half maximumf the (4 2 0), (4 2 2), (4 3 1), (5 2 1), (5 3 2), (4 4 4),(6 4 2) reflections and for the powder samples of

(4 0 0), (4 2 0), (4 2 2), (5 2 1), (5 3 2), (4 4 4), (6 4 0)reflections. The FWHM was corrected for instru-

adening. The FWHM data did not give evidence forcrystallite shapes or crystallographic strain. Mor-

d thickness of the films were observed using FE-SEM55 field emission scanning electron microscope withtector.sity of the Er and Yb doped Y3Al5O12 pellets1200 C was measured by Archimedes method using. Morphology and grain size of the fracture surfaceere studied by low vacuum scanning electron micro-EM) (Hitachi S-3400N, Hitachi, Japan).

escence measurements

solved fluorescence decays were recorded using00 U fluorescence lifetime spectrometer systemresolved excitation and emission monochromatorsThe IBH 5000XeF sub-microsecond xenon flash-sed for multi-channel scaling (MCS) measurements.

was equipped with a TBX-04 picosecond photonodule for detection in the UV/visible and a Hama-PMT module (H9170-5) for detection in the rangem. Melles Griot coloured glass filters were used tored light from the excitation source as well as block-

ted light from the laser source. The luminescences were measured and analyzed using multi-channelCS) along with the IBH Data Station v 2.1 softwaren of the spectrometer and analysis of the decay traceseconvolution-fits. Excitation and emission spectraned by locking the emission and excitation wave-spectively, monitoring the detector response whilee appropriate monochromator.suring the luminescence upon sequential multipho-ion, the films were excited with a 980 nm cw dioderlabs), focused on the film surface. Luminescencere collected by a lens coupled to an optical fibered by a Hamamatsu Photonic Multichannel Analyzer3).

llisation and phase purity of bulk powders

ination temperature of the YAG was evaluated froms of the YAlO gel powders. The TG curve pre-


Fig. 2. Thermogravimetrical analysis of the decomposition of the YAlO pre-cursor gel.

sented in Fig. 2 demonstrates that the decomposition of theorganic part of the gel occurred around 300 C, while a minorweigh loss ders anneathe gel waposes to anoxide powdcompletely(XRD). Futallite grow

XRD oftions afterand no impEr2O3 or Ythe powderand the denoretical. That 1200 Cobtained.

Fig. 3. X-rayYAlO gel a

Fig. 4. X-raY3Al5O12:Er(5%), Y3Al5Oat 1200 C.

hin

sur

deted fiy pac(d)).in thdippO12:(e))rystaonfi

.

BrafilmlineS Nases such as YAP and YAM were observed. The averagelite size of the deposited films was estimated to beis observed until 800 C. XRD of YAlO gel pow-led at different temperatures (Fig. 3) confirmed thats amorphous (not shown) and that the gel decom-amorphous oxide at around 300 C. The amorphouser starts to crystallize at 700 C and at 850 C it iscrystallized with crystallite size of about 70 5 nm

rther annealing at higher temperature resulted in crys-th.Er/Yb:YAG powders confirmed that all composi-

heat treatment at 1200 C (Fig. 4) were phase pureurity phases such as YAlO3 (YAP), Y4Al2O9 (YAM),b2O3 were observed. The average crystallite size ofs sintered at 1200 C was calculated to be 88 5 nmsity of pellets annealed at 1200 C was 50% of the-e cross-section SEM analysis of pellets heat treated

confirmed that porous nano-crystalline samples were

3.2. T

Theof thedeposidensel(Fig. 5to besingleY3Al5(Fig. 5nano-c

1m c40 nm

TheYAGcrystal(JCPDate phcrystaldiffraction patterns of YAG powders derived from precursornnealed at 600900 C.

27 5 nm.

3.3. Photo

The sam(5%), Y3Acharacterisfor excitatiThe main eto the intrasentative exmonochrom1530 nm arobserved a525 and 66excitationy diffraction patterns of Y3Al5O12:Er,Yb (2:1) (1%),,Yb (1:1) (1%), Y3Al5O12:Er,Yb (1:2) (1%), Y3Al5O12:Er

12:Er (10%) and Y3Al5O12:Er (20%) powder samples annealed

lms

face morphology and cross-section FE-SEM imagesposited YAG films are shown in Fig. 5. Thelms appear smooth and homogeneous and consist ofked nano-crystalline grain after annealing at 900 CThe thickness of the deposited films was determinede range of 200250 nm showing that thickness pered layer was 4050 nm. Cross-section image of theEr,Yb (1:1) (2%) film deposited from the modified soldemonstrates a homogeneous film of densely packedlline particles. The thickness of the deposited film is

rming that the thickness per single dipped layer was

gg reflections in the XRD pattern of the depositedannealed at 900 C were assigned to the poly-YAG phase which is consistent with literature

o. 3340) (data not presented). No other intermedi-luminescence properties

ples of Y3Al5O12:Er,Yb (1:2) (1%), Y3Al5O12:Erl5O12:Er (10%) and Y3Al5O12:Er (20%) showed

tic Er3+ luminescence between 1350 and 1600 nmon in the UV and visible region as shown in Fig. 6.mission peak occurs at 1530 nm and is attributed-4f 4I13/2 4I15/2 transition of the Er3+ ion. Repre-citation spectra obtained by scanning the excitationator while monitoring the Er3+ luminescence at

e presented in Fig. 7. The main excitation peaks aret 455 and 255 nm, with weaker features observed at0 nm. The absorption channels correspond to directof the transitions 4I15/2 4F5/2 (455 nm emission),


Fig. 5. Surface and cross-sectional FE-SEM images of YAG (one layer film annealed at 350 C (a); five layer films annealed at 600 C (b) and five layer filmsannealed at 900 C (c) and (d)) and Y3Al5O12:Er,Yb (1:1) 2 mol% doping (30-layer film annealed at 900 C (e)) films derived from 0.25 M dip-coating sols.

Fig. 6. Emisison spectra of Y3Al5O12:Er,Yb (1:2) (1%), Y3Al5O12:Er (5%),Y3Al5O12:Er (10%) and Y3Al5O12:Er (20%) pellets samples under 455 nmexcitation.

Fig. 7. Excitation spectra of Y3Al5O12:Er,Yb (1:2) (1%) and Y3Al5O12:Er (5%)pellets samples.


Fig. 8. TimeY3Al5O12:ErY3Al5O12:Er

4I15/2 2Demission) a

Time rethe relaxat4I13/2 4IFig. 6, fordepicted ina long decobserved fEr3+ increaa decay timfaster dropcross-relax

The samthe visibleY3Al5O12:lets subjeclatter has tdistinct pearesolved mCompared670 and 7constantsanalysis isthe appearferences inas the dectration asin the IR.

3.4. Up-co

It was asequentialtoring the980 nm. Em

Time decay curves at 670 nm under 295 nm excitation of12:Er,Yb (2:1) (1%), Y3Al5O12:Er,Yb (1:1) (1%) and Y3Al5O12:Er,Yb

) pellets samples. The continuous lines are fitting curves.

. 10. The observed luminescence peaks in the visibleat 520570 and 640680 nm are due to the radiative

ionsemisY3AO12:trati

on intionscenscenhinas o

pingate odecay curves at 1530 nm under 455 nm excitation of,Yb (1:2) (1%), Y3Al5O12:Er (5%), Y3Al5O12:Er (10%) and(20%) pellets samples. The continuous lines are fitting curves.

7/2 (255 nm emission), 4I15/2 2H11/2 (525 nmnd 4I15/2 4F9/2 (660 nm emission).solved measurements gave further information ofion of the Er3+ levels. The decay times of the15/2 transition for the same samples as shown inexcitation at 455 nm and emission at 1530 nm, areFig. 8. For the low Er3+ concentration one observes

ay time of 10 ms, which is of similar magnitude asor Er3+ in Er,Yb:YAG.35,36 As the concentration ofses the luminescence gradually is quenched to reache of 2.2 ms for the sample with 20% of Er dopant. Theof the decays for higher Er3+ concentrations suggestation process to be involved.ples also exhibited weak luminescence emission in

. Emission spectra of Y3Al5O12:Er,Yb (2:1) (1%),Er,Yb (1:1) (1%), Y3Al5O12:Er,Yb (1:2) (1%) pel-ted to excitation pulses at 295 nm showed that thehe most intense emission in the visible region with

Fig. 9.Y3Al5O(1:2) (1%

in Figregiontransit(greentively.Y3Al5concen

emissicentraluminelumine(2%) tratio wlow dodominks at 670 and 770 nm (data not shown). The time-easurements resulted in the decays as shown in Fig. 9.to the emission in the IR, the emission decays at

70 nm were not mono-exponentials and two decayhad to be assumed to fit all cases. The detailed

summarized in Table 1. As can be judged fromance of the decay traces there are only minor dif-

the decay times for the emissions in the visibleay times are hardly changed with dopant concen-was observed for the 4I13/2 4I15/2 luminescence

nversion photoluminescence

lso investigated the possibility to stimulate furtherexcitation of the Er3+ doped samples by moni-up-conversion photoluminescence by excitation at

ission spectra of the bulk samples are presented

Fig. 10. PL uY3Al5O12:ErY3Al5O12:Er1200 C afterin the Er3+ ions from 2H11/2 and 4S3/2 to 4I15/2sion), and from 4F9/2 to 4I15/2 (red emission), respec-l5O12:Er,Yb (2:1) (1%), Y3Al5O12:Er,Yb (1:1) (1%),Er,Yb (1:2) (1%) bulk samples with low dopingons showed higher green emission intensity thantensity in the red spectra region. When the Er3+ con-increases from 5, 10 to 20%, the red up-convertedce intensity is enhanced. In up-conversion photo-ce emission spectrum of the Y3Al5O12:Er,Yb (1:1)film sample the same green/red emission intensitybserved (data not shown). For thin film samples with

concentration 2H11/2/4S3/2 4I15/2 was found tover 4F9/2 4I15/2 transition.p-conversion emission spectra of Y3Al5O12:Er,Yb (2:1) (1%),,Yb (1:1) (1%), Y3Al5O12:Er,Yb (1:2) (1%), Y3Al5O12:Er (5%),

(10%) and Y3Al5O12:Er (20%) pellets samples annealed atIR exitation at 980 nm (150 mW, 500 ms).


Table 1Decay times for emision at 670 and 770 nm for Y3Al5O12:Er,Yb (2:1) (1%), Y3Al5O12:Er,Yb (1:1) (1%) and Y3Al5O12:Er,Yb (1:2) (1%) pellets samples annealedat 1200 C, excited at 295 nm. The value in parenthesis behind the decay constants is the relative weight for each component of the fit.

Sample nm

Y3Al5O12:Er,

Y3Al5O12:Er,

Y3Al5O12:Er,

4. Discuss

The aqustrated toroute was anano-crystaAccordingappear crawere also sgrains in troute, mulcalcinationmulti-dippisimilar momethod.

The filmgood wettaadhesion stOther concwetting agehigher conca thick, inhother hand,decrease inwas regard

In the filfine pores wtemperaturdensificatiofilm surfacannealing thowever shdip-coatingYAG thin fiby this sim

The optby the presreported foroutes.14,23

in detail.The pos

characterisused system1.5m, buplete 4f ele

resul, a q+ ios thee lu

ystemesidmu

2Ys, thto Ertionauseb3+

em

echay traia t

2F4I

tonthescencon

ant ms Er3SA)iativIR

the mionre steve

e wol%Decay ms (rel. weight %) at 670Yb (2:1) (1%) 1 = 0.388 (24%)

2 = 1.28 (76%)Yb (1:1) (1%) 1 = 0.389 (13%)

2 = 1.11 (86%)Yb (1:2) (1%) 1 = 0.507 (23%)

2 = 1.39 (77%)

ion

eous chemical solution deposition route was demon-produce single phase YAG powders. The solgellso demonstrated to yield homogeneous, smooth andlline YAG films on silicon substrates by dip-coating.to the surface morphology (Fig. 5(ad)), the films

ck-free, smooth and homogeneous. The thin filmshown to consist of densely packed nano-crystallinehe range 27 5 nm. To simplify the preparation

ti-dipping deposition (five immersions before each) was also performed. The films produced by theng procedure and calcined at 900 C exhibited veryrphology as films deposited by the single dipping

s completely covered the substrate which indicatesbility of the solution on the substrates and significantrength between the substrate and the deposited layer.entrations of PVA solutions (1, 2, 5 and 10%) asnt were also tested in the dip-coating procedure. Theentrations of the PVA solution led to the formation ofomogeneous layer of deposited YAlO gel. On thethe low concentrations of PVA led to an undesirablethe wettability of the substrate, hence a 3% solution

ed as the optimum.ms annealed at 600 C, homogeneous distribution ofas observed (Fig. 5(b)). With increasing annealing

e up to 900 C, the porosity decreased leading to filmn. It should be noted that density gradients along the

e was observed. Hence, further optimization of e.g.,emperature is necessary to remove all porosity. It wasown, that with careful control of sol composition andconditions it is possible to produce nano-crystalline

lms without the presence of other intermediate phasesple aqueous route.

shellsticularthe Er3trationincreasEr3+ sture. Bexcitedof 2F5/reason

ferredinterac

Becand YStokestwo m(energative v2F5/2 4I11/2 by phoand toluminedopingdominprocestion, GnonradsecondFromrelaxatare mo

Howincreasto 20 mical properties of the (Er, Yb) doped YAG preparedent solgel synthesis were similar to the propertiesr similar materials prepared by another preparationIn the following the optical properties are discussed

ition of the luminescence bands in the spectrum istic for a specific lanthanide ion. The Er3+ is a widely

in fiber optics and photonics due to its emission att it also emit in the visible region. Er3+ ion has incom-ctronic shell which is shielded by closed 5s and 5p

energy tran4I1/2 24Fquently, themission frparison wit

5. Conclu

The preroute to YADecay ms (rel. weight %) at 770 nm1 = 2.72 (14%)2 = 10.4 (86%)1 = 3.20 (17%)2 = 10.1 (83%)1 = 3.54 (19%)2 = 11.5 (81%)

ting in rather sharp luminescence bands.37,38 In par-uantum efficiency of the 4I13/2 4I15/2 transition inn is very high.39 However, for low Er3+ ion concen-

absorption coefficients are very small. In order tominescence generally Yb3+ is used as co-dopant for

s which has a very simple ff energy level struc-es the 2F7/2 ground multiplet, there is only the 2F5/2ltiplet at around 1m in Yb3+ ion. Also, the energyb3+ state is very similar to 4I11/2Er3+ state. For thesee energy is mostly absorbed by Yb3+ ion and trans-3+ ion (2F5/2(Yb3+) 4I11/2(Er3+)) by dipole-dipole.35

of possible energy level transitions both Er3+ions are used extensively in up-conversion (anti-ission) process. In ErYb up-conversion process,nisms ESA (excited state absorption) and ETUnsfer up-conversion) are involved. ESA is oper-

he channel 4I15/2 4I11/2 4F7/2 and ETU from7/2:4I11/2 4F7/2 (of neighbouring Yb3+) and from15/2:4I11/2 4F7/2 (of neighbouring Er3+), followedrelaxation to the 2H11/2 or 4S3/2 for green emission4F9/2 for the red emission.3942 The up-conversionce is very weak in the samples with 1 mol% Er/Ybcentrations. At low doping concentrations the pre-echanism is excited state absorption (ESA). In this

+ by absorbing the IR photon (ground state absorp-is excited to the 4I9/2 level from where it relaxes

e to the 4I11/2 level. By subsequent absorption ofphoton, the 4I11/2 4F3/2 transition occurs (ESA).etastable 4F3/2 level, the nonradiative multiphoton

(NR) can occur to the 4S3/2 and 4F9/2 levels, whichable than 2F5/2, 4F7/2 or 2H11/2 levels.r, the absolute intensities in the bulk materialsith increasing Er3+ doping concentration from 5. At high doping concentrations the cooperativesfer (CET) process (4F7/2, 4I11/2 24F9/2 and 4S3/2,9/2) operate between two nearby Er3+ ions. Conse-

e 2H11/2 4I15/2 has very weak intensity and theom 4F9/2 to 4I15/2 becomes more dominant in com-h 2H11/2, 4S3/2 to 4I15/2 transitions.

sion

sent report demonstrate a successful aqueous solgelG powders and thin film using nitrate cation pre-


cursors, acetic acid as complexing agent and ethylene glycol aspolymerization agent. The gels were shown to decompose toan amorphgel was chpure YAGof the aqudemonstratStokes emreported. TStokes emiof the dopa

Reference

1. Hirata Gblue lum

2. Potdevinuum ultrJ Appl P

3. ZorenkoG, Mikhdoped YAJ Lumin

4. Uhlich Dzation ofEu3+. Op

5. RabinovnanometMater P

6. Pullar RCical propaluminiucursor. J

7. Karato Sgarnet si

8. BonnerMater 19

9. Van dercence in1981;38

10. Rotmancrystals:cerium-d

11. RotmanIII. Thedoped yt

12. Schuh Lof Ca- a1989;66

13. RobertsoFilms 19

14. Wang Wtions betsubmicro

15. Hsu CT,substrate

16. Mizogucand Y3FCeram S

17. ParukuttH, Pariseplasma s

18. Diaz-TorNieto J.depositio

19. Hay RS. Phase transformations and microstructure evolution in solgelderived yttriumaluminium garnet films. J Mater Res 1993;8(3):578604.

Y-C,ived Yma C,3. p.Y-C

ractedifferi GR,n film4;64PY, Lpertie

n filmsta VC3+

-do3+

. Chber M0;12mmof ru

ts ass

wa Mxes: e

ough

stbergB,

tinum6;39dgrenctronacety

uit P-ATwo-s in th9;21htel Wldinght-harstbergrphyri4;16ba R,n M,tinumnct Mker Dord Cweizde puY2SiOnker Biskev

nsferhi MOptied n5;27

lman7;82

zel F.em Renyonctronious oxide and the crystallisation of the amorphousaracterized. Fabrication of homogeneous, crack-freeand Er/Yb-doped YAG thin films by dip-coatingeous sol deposited on Si (1 1 1) substrates wereed. The photoluminescence up-conversion (anti-ission) properties of the Er,Yb:YAG materials arehe photoluminescence as well as up-conversion (anti-ssion) processes demonstrated significant influencent level.

s

A, Mckittarick J, Devlin D. Growth and analysis of red, green andinescent oxide thin films. Surf Rev Lett 1998;5(1):4137.A, Chadeyron G, Boyer D, Mahiou R. Optical properties upon vac-

aviolet excitation of solgel based Y3Al5O12:Tb3+, Ce3+ powders.hys 2007;102(7):07353673546.Yu, Gorbenco V, Konstankevych I, Voloshinovskii A, Stryganyukailin V, Kolobanov V, Spassky D. Single-crystalline films of Ce-G and LuAG phosphors: advantages over bulk crystals analogues.

2005;114(2):8594., Huppertz P, Wiechert DU, Jstel T. Preparation and characteri-nanoscale lutetium aluminium garnet (LuAG) powders doped byt Mater 2007;29(11):15059.

itch Y, Bogicevic C, Karolak F, Tetard D, Dammak H. Freeze-driedric neodymium-doped YAG powders for transparent ceramics. Jrocess Technol 2008;199(13):31420.

, Taylor MD, Bhattacharya AK. The sintering behaviour, mechan-erties and creep resistance of aligned polycrystalline yttriumm garnet (YAG) fibres produced from an aqueous solgel pre-Eur Ceram Soc 1999;19(9):174758., Wang Z, Fujino K. High-temperature creep of yttriumaluminumngle crystals. J Mater Sci 1994;29(24):645862.WA. Epitaxial growth of garnets for thin film lasers. J Electron74;3(1):193208.Weg WG, van Tol MW. Saturation effect of cathodolumines-rare-earth activated epitaxial Y3Al5O12 layers. Appl Phys Lett

(9):7057.SR, Tandon RP, Tuller HL. Defectproperty correlations in garnetThe electrical conductivity and defect structure of luminescentoped yttrium aluminium garnet. J Appl Phys 1985;57(6):19515.SR, Tuller HL. Defect-property correlations in garnet crystals.

electrical conductivity and defect structure of luminescent nickel-trium aluminium garnet. J Appl Phys 1987;62(4):130512., Metselaar R, de With G. Electrical transport and defect propertiesnd Mg-doped yttrium aluminium garnet ceramics. J Appl Phys(6):262732.n JM, van Tol MW. Cathodoluminescent garnet layers. Thin Solid84;114(12):22140.-N, Widiyastuti W, Ogi T, Lenggoro IW, Okuyama K. Correla-ween crystallite/particle size and photoluminescence properties ofmeter phosphors. Chem Mater 2007;19(7):172330.Yen SK. Electrochemical synthesis of thin film YAG on inconel. Electrochem Solid-State Lett 2006;9(4):D912.hi Y, Kagawa M, Syono Y, Hirai T. Film synthesis of Y3Al5O12e5O12 by the spray-inductively coupled plasma technique. J Amoc 2001;84(3):6513.yamma SD, Margolis J, Liu H, Grey CP, Sampath S, Herman

JB. Yttrium aluminum garnet (YAG) films through a precursorpraying technique. J Am Ceram Soc 2001;84(6):19068.res LA, De la Rosa E, Salas P, Angeles-Chavez C, Arenas LB,Nanoparticle thin films of nanocrystalline YAG by pulsed lasern. Opt Mater 2005;27(7):121720.

20. WuderAr200

21. Wuchaby

22. Bathi199

23. Jiaprothi

24. CoEuEu

25. We199

26. Glotiessal20.

27. Kaplethr96.

28. Veson

pla200

29. LinEle(II)

30. BoC.dye200

31. Dicbuilig

32. VePo200

33. ZiegreplaFu

34. ParCo

35. SchdioEr:

36. DePastra

37. NisK.dop200

38. Po199

39. AuCh

40. KeeleParola S, Mugnier J. Preparation and characterization of solgelAG optical planar waveguide. Advances in optical thin films. In:Kaiser N, Macleod HA, editors. Proceedings of SPIE, vol. 5250.5818., Parola S, Marty O, Villanueva-Ibanez M, Mugnier J. Structuralrizations and waveguiding properties of YAG thin films obtainedent solgel processes. Opt Mater 2005;27(9):14719.Chang HLM, Foster CM. Preparation of single-crystal Y3Al5O12

by metalorganic chemical vapour deposition. Appl Phys Lett(14):17779.in J, Han XM, Yu M. Pechini solgel deposition and luminescences of Y3Al5xGaxO12:Ln3+ (Ln3+ = Eu3+, Ce3+, Tb3+; 0 x 5)s. Thin Solid Films 2005;483(12):1229.

, Lochhead MJ, Bray KL. Fluorescence line-narrowing study ofped solgel silica: effect of modifying cations on the clustering ofem Mater 1996;8(3):78390.J. Science and technology of laser glass. Non-Cryst Solids

3(13):20822.WR, Volden S, Sjblom J, Lindgren M. Photophysical proper-thenium(II) tris(2,2-bipyridine) and europium(III) hexahydrate

embled into solgel materials. Chem Mater 2005;17(22):5512

, Frechet JMJ. Self-assembled lanthanide-cored dendrimer com-nhancement of the luminescence properties of lanthanide ionssite-isolation and antenna effects. Chem Mater 1998;10(1):286

R, Westlund R, Eriksson A, Lopes C, Carlsson M, Elias-Glimsdal E, Lindgren M, Malmstrm E. Dendron decorated(II) acetylides from optical power limiting. Macromolecules

(6):223846.M, Minaev B, Glimsdal E, Vestberg R, Westlund R, Malmstrm E.

ic states and phosphorescence of dendron functionalized platinumlides. J Lumin 2007;124(2):30210., Kamada K, Feneyrou P, Berginc G, Toupet L, Maury O, Andraud

photon absorption-related properties of functionalized BODIPYe infrared range up to telecommunication wavelengths. AdvMater

(1011):11514.R, Hecht S, Frchet JMJ. Functionally layered dendrimers: A new

block and its application to the synthesis of multichromophoricvesting systems. Org Lett 2005;7(20):44514.

R, Nystrom A, Lindgren M, Malmstrom E, Hult A.n-cored 2,2-bis(methylol)propionic acid dendrimers. ChemMater(14):2794804.Desroches C, Chaput F, Carlsson M, Eliasson B, Lopes C, Lind-Parola S. Preparation of functional hybrid glass material from(II) complexes for broadband nonlineat absorption of light. Adv

ater 2009;19(2):23541.. Luminescent lanthanide sensors for pH, pO2 and selected anions.hem Rev 2000;205:10930.er T, Jensen T, Heumann E, Huber G. Spectroscopic properties andmped 1.6m laser performance in Yb-codoped Er:Y3Al5O12 and

5. Opt Commun 1995;118(56):55761., Galagan B, Osiko V, Sverchkov S, Balbashov AM, Hellstrm JE,

icius V, Laurell F. Yb3+, Er3+:YAG at high temperatures: Energyand spectroscopic properties. Opt Commun 2007;271(1):1427.

, Tanabe S, Inoue M, Takahashi M, Fujita K, Hiraocal-telecommunication-band fluorescence properties of Er3+-anocrystals synthesized by glycothermal method. Opt Mater(4):65562.A. Erbium implanted thin film photonic materials. Appl Phys Lett(1):139.Upconversion in anti-Stokes processes with f and d ions in solids.v 2004;104(1):13974.AJ. Recent developments in rare-earth doped materials for opto-cs. Prog Quantum Electron 2002;26(45):22584.


41. Strmpel C, McCann M, Beaucarne G, Arkhipov V, Slaoui A, Svrcek V,del Canizo C, Tobias I. Modifying the solar spectrum to enhance siliconsolar cell efficiencyan overview of available materials. Sol EnergyMaterSol Cells 2007;91(4):23849.

42. Qin G, Lu J, Bisson JF, Feng Y, Ueda K, Yagi H, Yanagitani T. Upconver-sion luminescence of Er3+ in highly transparent YAG ceramics. Solid StateCommun 2004;132(2):1036.

Luminescent properties of rare earth (Er, Yb) doped yttrium aluminium garnet thin films and bulk samples synthesised by an aqueous sol-gel techniqueIntroductionExperimentalSynthesis of the sols, gels and powdersThin films processing by dip-coatingMorphology and structure characterizationLuminescence measurements

ResultsCrystallisation and phase purity of bulk powdersThin filmsPhotoluminescence propertiesUp-conversion photoluminescence

DiscussionConclusionReferences

[6]

Documents