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Spectrochimica Acta Part A 70 (2008) 99103

Investigation of thermal stability and speste

an Unly 20

Abstract

A series o 0, 3,of WO3 on ped ncontent incre (FWHthe measure 02188.9%, respe commay be a po 2007 Pub

Keywords: Te iency

1. Introdu

Rare-earth-doped optical glasses are important materials foroptical fibers, optical amplifiers, and waveguide lasers [1,2]. Dueto the increasing demand for information capacity of wavelengthdivision multiplexing (WDM) networks, Er3+-doped telluriteglasses andlated emissattracted siA high gainreported fo[5], whichsuch as higand corrosiits poor glnomenon m

Recentlniobic telluand presenEr3+:4I13/2a large num[8] reported

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study of the spectroscopic properties and thermal stability ofTeO2Nb2O5WO3 glasses. Thus, in this article, we focusedon the analysis of the effect of WO3 content on the spectro-scopic properties of Er3+/Yb3+ co-doped niobic tellurite glasses.

1386-1425/$doi:10.1016/jtellurite-based fiber amplifiers with large stimu-ion cross-section and broad fluorescence width havegnificant attention for broadband applications [3,4].

of 50 dB and a wide bandwidth of 76 nm have beenr an Er3+-doped tellurite fiber pumped at 1480 nmalso exhibited various excellent material propertiesh refractive index, high dielectric constants, strengthon resistance and rare-earth ion solubility. However,ass thermal stability and strong upconversion phe-ade it difficult to used in practice [4].

y, Lin et al. [6], and Dai et al. [7] reported Er3+-dopedrite glasses, which exhibited good thermal stabilityted broadband properties. However, the lifetime oflevel in niobic tellurite glass is relative lower due tober of Nb2O5 with high refractive indices. Xu et al.the Er3+-doped niobic tungsten tellurite glass shows

580 8180705; fax: +86 580 8180705.dress: wxm@zjou.net.cn.

Especially, the effect on the thermal stability, the FWHM, thestimulated emission cross-section, the lifetime of the 4I13/2 levelare analyzed and discussed.

2. Experimental

2.1. Sample preparations

The glasses were synthesized by a conventional melting andquenching method from reagent-grade powders of Nb2O5, WO3,and TeO2. Glass samples were prepared according to the fol-lowing compositions in mol%: 75TeO2(25 x)Nb2O5xWO3,where x = (0, 3, 6, 9, 12, and 15 mol%), and the sampleswere named as TNW1TNW5 for short. All glasses contained0.5 mol% Er2O3 as an active dopant and 2.5 mol% Yb2O3 as asensitizer, which were introduced as with 99.99% purity, respec-tively. About 15 g batches of starting materials were fully mixedand then melted in platinum crucibles at 850950 C in anelectronic furnace for 3040 min. For reducing OH content

see front matter 2007 Published by Elsevier B.V..saa.2007.07.013Er3+/Yb3+ co-doped niobic tungXuming Wang

College of Mathematics, Physics and Information, Zhejiang OceReceived 20 April 2007; received in revised form 7 Ju

f novel Er3+/Yb3+ co-doped 75TeO2(25 x)Nb2O5xWO3 (TNW: x =the thermal stability and spectroscopic properties of Er3+/Yb3+ co-doasing from 0 to 15 mol%, the fluorescence full width at half maximum

d lifetime (m), and quantum efficiency () change from 71 nm, 8.47 1ctively. The FWHM and peake of Er3+ ions in different glass hosts were

tentially useful candidate material host for broadband amplifiers.lished by Elsevier B.V.

O2Nb2O5WO3; Thermal stability; Spectroscopic properties; Quantum effic

ction good sto thectroscopic properties inn tellurite glasses

iversity, Zhejiang 316000, PR China07; accepted 11 July 2007

6, 9, 12, and 15 mol%) glasses have been prepared. Effectiobic tellurite glasses have been investigated. With WO3M), the peak of stimulated emission cross-section (peake ),

cm2, 2.86 ms, 84.1% to 76 nm, 7.22 1021 cm2, 3.14 ms,pared; the obtained data reveals that this new TNW4 glass

roscopic properties and thermal stability. However,knowledge of the authors, there has been no detailed

100 X. Wang / Spectrochimica Acta Part A 70 (2008) 99103

Table 1The compositions and physical properties of the TNW glasses

Codes 3 NEr/NYb (1020 ion/cm3) a (1021 cm2)TNW1 1.609/8.045 7.953TNW2 1.562/7.810 7.614TNW3 1.527/7.635 7.412TNW4 1.473/7.365 7.223TNW5 1.421/7.105 6.923TNW6 1.379/6.895 6.532

drying prohigh-purityliquids weto room teished carefthe require

2.2. Prope

The denprinciple. Rthermal stasis (DTA) mYb3+ concple densitierecorded otometer. ThspectrophoThe fluoreslight pulsesto obtain arecorded otial functiowere taken

3. Results

3.1. Therm

Table 1concentrati

Fig. 1 shsition tempand the difas a roughstability [9crystallizatloss of thedesirable foFig. 1, it caing WO3 mof WOTAnd the WO3, reacCompared

2 C, T = 128 C) glass, which was always reported asising candidate host for fiber devices because of goodl stability [4], the value of T of TNW4 glass are 36 Cthan TZN glass. The results demonstrate that these TNWs are very stable against devitrification and they are moree for fiber drawing.

bsorption spectra

. 2 shows absorption spectra of Er3+/Yb3+ co-doped, TNexcit thety owbroationtheb3+orpt

by [12.

log(s inthe g:4I1Composition (mol%) (g/cm ) n75TeO225Nb2O5 5.482 2.18175TeO222Nb2O53WO3 5.521 2.15275TeO219Nb2O56WO3 5.563 2.11375TeO216Nb2O59WO3 5. 617 2.07775TeO213Nb2O512WO3 5.645 2.04875TeO210Nb2O515WO3 5.684 2.013

cedures were applied. Glass melt was bubbled withoxygen. When the melting was completed, the glass

re poured into a stainless mold and then annealedmperature. The obtained glasses were cut and pol-ully to 10 mm 10 mm 1.2 mm in order to meetments for optical measurements.

rty measurements

sities were measured according to the Archimedesefractive indices were measured with SPA-4000. Thebility was determined by differential thermal analy-

ethod at a heating rate of 10 C/min. The Er3+ andentrations were calculated from the measured sam-s and initial compositions. Absorption spectrum was

n a PERKIN-ELMER 900UV/VIS/NIR spectropho-e emission spectra were measured with a TRIAX550tometer on excitation at 975 nm laser diode (LD).cence lifetime of Er3+:4I13/2 level was measured withof 975 nm LD. The pulse modulation was performedlight pulse with 5s width. The decay traces were

n a digital oscilloscope and fitted by single exponen-ns to obtain the decay rates. All the measurementsat room temperature.

and discussion

al stability of the glasses

shows some basic physical properties, Er3+/Yb3+ons of TNW glasses.ows the compositional dependence of the glass tran-erature (Tg), crystallization onset temperature (Tx),ferent T (T = Tx Tg), which is usually chosenmeasure of glass formation ability or glass thermal]. Since fiber drawing is a reheating process and any

Tx = 43a promthermalargerglassesuitabl

3.2. A

FigTNW1to theous thaintensimuchabsorpthat ofonly Y

Absgiven

a() =

wheresamplecm3 inof Er3+ion during the process will increase the scatteringfiber and then degrade the optical properties, it isr a glass host to have T as large as possible. Fromn be found that the Tg and Tx increase with increas-onotonically. It can be attributed to the formation

e linkages with the increase of WO3 content [10].T first increases and then decreases with increasinghes the maximum value 164 C at x = 9 mol% [11].with 75TeO220ZnO5Na2O (TZN: Tg = 304 C, Fig. 1. CW3, TNW5 glasses. Each assignment correspondsted level of Er3+ and Yb3+. From Fig. 2, it is obvi-absorption band around 980 nm has a strong opticaling to the absorption of Yb3+, because Yb3+ has a

der absorption band from 870 to 1060 nm, and thecross-section of Yb3+ is about 10 times larger thanEr3+ [12]. It is therefore reasonable to assume thatcontributes to this absorption line.ion cross-section of a ground state absorption, a, is3]:303 log(I0/I)

NL(1)

I0/I) is the absorbance, L the thickness of the glasscm, and N is the rare-earth (RE) concentration perlass. As seen in Table 1, the absorption cross-section

5/2 4I13/2 of TWB glasses decreases with increas-ompositional dependence of Tg, Tx, and T of TNW glasses.

X. Wang / Spectrochimica Acta Part A 70 (2008) 99103 101

Fig. 2. Absorption spectra of Er3+/Yb3+ co-doped TNW glasses.

ing WO3 content. The reason can be attributed to the decreaseof Nb2O5 content [7].

3.3. Emisscross-sectio

Fig. 3 shTNW5 glaamplitudeFWHM onFig. 3, it cdecreases wwhen WO3are sub-com1503.5, 1526.2, and 5also can beat 1503.5 abroadening

Fig. 3. The em

Fig. 4. The abin TNW4 glas

Accordision cross-ions can be

are r

a

h ise netateulated inemi

mberseen

f Erle 2ross-

ost.es welecion spectra and stimulated emissionn

ows the emission spectra of Er3+ in TNW1, TNW3,sses; the dotted lines are the deconvolved Gaussianpeaks fitted and the insert shows the dependence of

WO3 content of TNW glasses. From the inset ofan be seen that the FWHM first increases and thenith increasing WO3, reaches the maximum is 76 nmis 9 mol% [14,15]. The curves with broken linesponent peaks, A, B, C, and D, which correspond to

30, 1553, and 1586 nm, and the width are 37.2, 18,2.2 nm of TNW5 glass, respectively. From Fig. 3, itfound that the emission of sub-components peakednd 1586 nm may have the main contribution to theof Er3+:4I13/2 4I15/2 transition [16].

which

e() =

where is th4I15/2 sbe calcprovidulatedMcCucan be

peake o

Tabsion cglass hincreasto theission spectra of Er3+:4I13/2 4I15/2 transition in TNW glasses.

the refractiFrom Tabllarger refraemission cFWHM andeficial to thFWHM the bandwiamplifier. Thosts indicas a host m

3.4. Lifetim

The lifeEr3+:4I13/2sorption cross-section (a), stimulated emission cross-section (e)s.

ng to the McCumber theory [17], the stimulated emis-section e() of the 4I13/2 4I15/2 transition of Er3+calculated from the absorption cross-section a(),

elated by

() exp[ h

kT

](2)

the Plancks constant, k the Boltzmann constant, andt free energy required to excite one Er3+ from theto 4I13/2 state at temperature T. The a() and caned from the absorption spectra and using the method

Ref. [18]. The absorption cross-section (a), stim-ssion cross-section (e) of Er3+ ions calculated bytheory of TNW4 glass is shown in Fig. 4. Cleary, itthat the peak of stimulated emission cross-section

3+ ions in TNW4 glass reaches 7.98 1021 cm2.lists the refractive index n, and the peak of emis-section peake and FWHM of Er3+ ions in differentPrevious studies [4] have shown the e value can beith increasing refractive index of a glass host due

tric dipole transition of rare-earth ions increases as

ve index of the glass host [e (n2 + 2)2/n] increase.e 2, it can be seen that the TNW4 glass has muchctive index, therefore it provides larger stimulatedross-section at 1.5m bands. Because the broaderthe larger stimulated emission cross-section are ben-

e amplificatory performance of EDFA, the value of

peake is often used as a semiquantitative indication of

dth. The larger the product, the better the properties ofhe comparison of FWHM peake in different glass

ates that the TNW4 glass is better than other glassesaterial for Er3+-doped for a broadband amplifier [23].

es and quantum efficiency

time of 4I13/2 level and quantum efficiency of 4I15/2 transition are directly related to the effect

102 X. Wang / Spectrochimica Acta Part A 70 (2008) 99103

Table 2The refractive index n, the peak of emission cross-section peake and FWHM in different glass hosts

Glass hosts n FWHM (nm) peake (1021 cm2) FWHM peake (1021 cm2 nm)Germanate [19] 1.625 53 5.70 302.1Silicate [20] 1.585 40 5.50 220.0Phosphate [21] 1.569 37 6.40Tellurite [22] 2.000 65 7.95TNW4 (this work) 2.077 76 7.98

Fig. 5. Fluorglass.

of laser pertroscopic acurve for 1by single esured lifeticompositiotum efficiein Fig. 6.increases w

Fig. 6. The cefficiency of E

Accordingstate is giv

1m = 1radwhere WMPtransfer rattrations inof Er3+ErTherefore,of measure

nt efrate.radi

s hav

2J2J escence decay cure for Er3+:4I13/2 4I15/2 emission of TNW1

the joidecay

Theglasse[25]:

rad =

formance and treated as key parameters in the spec-nalysis [23]. Fig. 5 shows the fluorescence decay.5m of Er3+ ions in TNW1 glasses, which is fittedxponential functions thus determining that the mea-me m of the 4I13/2 level is 2.86 ms, respectively. Thenal dependence of lifetime of 4I13/2 level and quan-ncy of Er3+:4I13/2 4I15/2 transition is also shownObviously, the lifetime and quantum efficiency allith an increasing of WO3 content monotonically.

ompositional dependence of lifetime of 4I13/2 level and quantumr3+:4I13/2 4I15/2 transition in TNW glasses.

where J anlevels, c ththe integrat is the methat the radcross-sectioincrementvalue of

be concludglass host hEr3+:4I13/2be neglecte

Since thlower thantution of Wlifetime bymultiphonostudied, the

= mrad

And the qusented in Fboth the radthe quantuto the decre236.8516.8606.4

to Ref. [9], the measured lifetime m of Er3+ exciteden by

+ WMP + WET + (3)

is the multiphonon decay rate and WET is the energye between Er3+ ions. Since the Er3+-doping concen-all of the samples are close, the energy transfer rate3+ ions should also be close for all of the samples.it can be deduced that the compositional dependenced lifetime of TNW glasses is mainly determined byfect of the radiative decay rate and the multiphonon

ative lifetimes of the 4I13/2 level of Er3+ ions in TNWe been calculated according to the follow relationship

+ 1+ 1

4

8cn2

abs() d(4)

d J are the total momentum for the upper and lowere speed of light, n the refractive index,

abs() d

ed absorption cross-section of the 1.5m band, andan wavelength of the absorption band. Eq. (4) revealsis inversely proportional to the integrated absorptionn

abs() d and the refractive index n. With theof theWO3 content, the value of n decrease, and theabs() d increase (see Table 1). From Fig. 6, it caned that for TNW glasses, the refractive indices ofas a dominant influence on the measured lifetime oflevel, and the effect of the value of

abs() d can

d.e phonon energy of tungsten tellurite glasses [7] isthat of niobic tellurite glasses [24], with the substi-O3 for Nb2O5 will lead to increase in the measureddecreasing the phonon energy of the glasses and then decay rate in the glass host. According to previousquantum efficiency () can be evaluated by(5)

antum efficiency for all glasses samples is also pre-ig. 6. Clearly, with an increasing of WO3 content,iative and the measured lifetime increase. Therefore

m efficiency increases from 84.1% to 88.9% owingase the multiphonon decay rate in the glass host.

X. Wang / Spectrochimica Acta Part A 70 (2008) 99103 103

4. Conclusion

The thermal stability and spectroscopic properties ofEr3+/Yb3+ co-doped TeO2Nb2O5WO3 glasses were investi-gated. It is found that the TNW4 glass shows broad emissionspectra at 1.55m band with a large stimulated emission cross-section, while keeps the lifetime and intensity relative high.Effect of WO3 content on 1.5m band emission were also ana-lyzed and discussed. The results indicate that in tungsten telluriteglasses, proper amount of WO3 can be used as a modifier toimprove broadband properties.

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Investigation of thermal stability and spectroscopic properties inpenalty -@M Er3+/Yb3+ co-doped niobic tungsten tellurite glassesIntroductionExperimentalSample preparationsProperty measurements

Results and discussionThermal stability of the glassesAbsorption spectraEmission spectra and stimulated emission cross-sectionLifetimes and quantum efficiency

ConclusionReferences