Research ArticleOptical Properties of Erbium Zinc Tellurite Glass System

Sidek Hj. Abdul Aziz,1 R. El-Mallawany,2 Siti Shawaliza Badaron,1

Halimah Mohamed Kamari,1 and Khamirul Amin Matori1

1Glass, Ceramic and Composite Research Group, Department of Physics, Faculty of Science, Universiti Putra Malaysia,43400 Serdang, Selangor, Malaysia2Physics Department, Faculty of Science, Menofia University, Shibin Al Kawm, Egypt

Correspondence should be addressed to Sidek Hj. Abdul Aziz; sidek@upm.edu.my

Received 16 October 2014; Revised 8 December 2014; Accepted 9 December 2014

Academic Editor: Jun Liu

Copyright © 2015 Sidek Hj. Abdul Aziz et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.

Er3+-doped tellurite glasses with molar compositions of xEr2O3-20ZnO-(80 − 𝑥)TeO

2(𝑥 = 0, 1, 2, 3, and 4 mole%) (EZT) have

been successfully synthesized by the melt-quenching method. Density and molar volume have been measured. UV-VIS absorptionspectra in the wavelength range of 400–800 nm at room temperature has been measured. The band gap for every compositionhas been calculated. Photoluminescence spectroscopy in the wavelength range of 400–650 nm and at room temperature has beenevaluated.

1. Introduction

Recently, tellurite glass has been used for lasing materialsand amorphous silicon solar cells [1, 2]. The properties of thehost material are very important to study before being dopedwith any rare-earth elements. Some of the fundamentalaspects of tellurite glasses such as glass structure, physical,thermal, optical, and other spectroscopy properties havebeen extensively studied [3–16]. Most of the research thatis emphasized particularly on tellurite glass doped withrare-earth element has been carried out. Erbium dopedtellurite glasses considerable literature has recently emergedconcerning the structure, optical, mechanical, thermal, andelectrical properties. The optical properties of glasses havebeen an important topic of continuing interest. For instance,the excellent optical properties of Er3+-doped gallium tellu-rite glasses that promising laser and amplifier material wasstudied [17].

The aim of this study is to synthesis and characterizationof the Er

2O3-ZnO-TeO

2(EZT) glass system. Density, molar

volume of glass, X-ray diffraction (XRD), and the chemicalcomposition of the glass samples will be measured. Absorp-tion and emission spectra through UV-Vis-NIR and photolu-minescence spectroscopy, respectively, will be measured.

2. Experimental Work

Glass samples were prepared by using tellurium dioxide(purity ≥ 99%), zinc oxide, ZnO (purity > 97%), and erbium(III) oxide (purity 99.9%). The powder chemicals wereweighed using an electronic digital weighting machine withan error of ±0.01 g. Each batch was then melted at 700–900∘C in the melting furnace. The melt was held at thistemperature for 30 minutes until a bubble-free liquid wasformed.Themelt was stirred to achieve desirable homogene-ity.The homogeneousmelt was quenched by pouring it onto apreheated stainless steel mold to avoid excess thermal shocks.The glasses were annealed for 1 hour at 10∘C higher than theglass transition temperature to release themechanical strains.The glass samples with molar compositions of 𝑥Er

2O3-

20ZnO-(80 − 𝑥)Te (𝑥 = 0, 1, 2, 3, and 4 mole%) (known asEZT) were successfully synthesized by the melt-quenchingmethod.The samples were cut into pieces having appropriatedimensions for absorption and emission optical and densitymeasurement [18].

The amorphous nature of each glass sample was con-firmed by using X-ray diffraction (XRD) and the chemicalcomposition of the glass samples was analyzed by usingenergy dispersive X-ray fluorescence (EDXRF). The bulk

Hindawi Publishing CorporationAdvances in Materials Science and EngineeringVolume 2015, Article ID 628954, 5 pageshttp://dx.doi.org/10.1155/2015/628954

2 Advances in Materials Science and Engineering

Table 1: Composition (mol%), molar mass, molar volume, and density of 𝑥Er2O3-20ZnO-(80 − 𝑥)TeO2 glasses.

𝑥𝐸r2O3(mol%)

ZnO(mol%)

(80 − 𝑥)TeO2(mol%)

Molar mass(g/mole)

Molar volume(cm3/mole)

Density(g/cm3)

Optical band gap𝐸opt (eV)

0 20 80 139.62 33.08 4.22 3.041 20 79 141.68 33.05 4.28 3.102 20 78 143.36 32.86 4.36 3.123 20 77 144.28 32.75 4.44 3.134 20 76 146.26 32.66 4.47 3.14

x: 0 x: 1 x: 2 x: 3 x: 4

Figure 1:The erbium doped 𝑥Er2O3-20ZnO-(80−𝑥)TeO

2(𝑥 = 0, 1,

2, 3, and 4mol%) (EZT) glass samples.

density of glass samples was measured using the Archimedesprinciple at room temperature and the molar volumes wereestimated quantitatively. All the glass samples were measuredusing XRD measurement system in the powder form. TheEDX analysis was performed by using the fluorescence X-rayspectrometer EDX-720/800HS/900HS/. UV-Vis spectropho-tometer (Lambda 35, Perkin Elmer) system has been usedwith sample thickness 1.88 to 2.04mm have been used.

3. Results and Discussion

Five of EZT glasses have been successfully prepared whereall glass samples are transparent, bubble-free, and homoge-neous. The glass color changes to be more growing pink withincreasing of erbium content as shown in Figure 1. Figure 2represents the XRD measurement EZT glass. Figure 2 showsa broad halo characteristic, which confirms the amorphousstructure.

Figure 3 shows that the density of EZT glass is increasedwith the addition of Er

2O3content. The increasing in density

of the glasses is due to the heavier erbium atomic mass ascompared to the other element in the glass samples. Theatomic mass of erbium is 167.259 which is heavier comparedto tellurium (127.60) and zinc (65.409). The molar volume(𝑉𝑚) of the glass samples has been calculated according to

𝑉𝑚=

𝑀glass

𝜌glass(cm3) (1)

𝑀glass ={(80 − 𝑥)𝑀TeO

2

+ 20𝑀ZnO + (𝑥)𝑀Er2O3

}

(100), (2)

where𝑀glass and 𝜌glass are the mass and density of the glasssample, respectively. Molar volume of tellurite glass sampleshas been plotted in Figure 3. As the Er

2O3content in the

EZT glasses increased, the density is also increased, hence

Inte

nsity

(a.u

.)

4mol%3mol%2mol%

1mol%0mol%

12 22 32 42 52 62 72 82 92

2𝜃 (deg)

Figure 2: The XRD pattern of the EZT glasses.

4.2

4.25

4.3

4.35

4.4

4.45

4.5

32.5

32.75

33

33.25

33.5

0 1 2 3 4 5

y = −0.0029x2 − 0.1026x + 33.102R2 = 0.9664

y = −0.0043x2 + 0.0831x + 4.2134R2 = 0.9887

Mol

ar v

olum

e (cm

3/m

)

Den

sity

(g cm

−3)

Er2O3 content (mol%)

Figure 3: The variation of density and molar volume of EZT glasssystem.

resulting in the decrease of 𝑉𝑚. Based on the result obtained,

the density and the molar volume of the EZT show anopposite trend. The increasing in density of the glasses is dueto the heavier Er

2O3molecular mass compared to the other

element in the glass system as shown in Table 1.The UV-Vis-NIR absorption spectra for glass system

ranging from 400 to 800 nm of wavelength are shown inFigure 4. It is found that optical absorption edge is not sharplydefined in the present glasses, which clearly indicates their

Advances in Materials Science and Engineering 3

(𝛼ℏ𝜔

)1/2

(cm

−1

eV)−

1

0mol% of Er2O344

42

40

38

36

34

32

30

28

26

3.00 3.05 3.10 3.15 3.20 3.25 3.30

(ℏ𝜔)

(a)(𝛼ℏ𝜔

)1/2

(cm

−1

eV)−

1

1mol% of Er2O3

3.00 3.05 3.10 3.15 3.20 3.25 3.30

55

50

45

40

35

30

(ℏ𝜔)

(b)

2mol% of Er2O3

3.00 3.05 3.10 3.15 3.20 3.25 3.30

80

70

60

50

40

30

(𝛼ℏ𝜔

)1/2

(cm

−1

eV)−

1

(ℏ𝜔)(c)

(𝛼ℏ𝜔

)1/2

(cm

−1

eV)−

13mol% of Er2O3

3.00 3.05 3.10 3.15 3.20 3.25 3.30

80

70

60

50

40

90

(ℏ𝜔)(d)

(𝛼ℏ𝜔

)1/2

(cm

−1

eV)−

1

4mol% of Er2O3

3.00 3.05 3.10 3.15 3.20 3.25 3.30

80

70

60

50

40

90

(ℏ𝜔)

(e)

Figure 4: Graph of quantity (𝛼ℏ𝜔)1/2 against photon energy (ℏ𝜔) for (80 − 𝑥)TeO2-20ZnO-𝑥 Er

2O3glasses.

4 Advances in Materials Science and Engineering

3.02

3.04

3.06

3.08

3.1

3.12

3.14

3.16

0 1 2 3 4 5Er2O3 content (mol%)

R2 = 0.9738

Opt

ical

ban

d ga

p,E

opt

(eV

)

y = −0.0079x2 + 0.0544x + 3.0443

Figure 5: The nonlinear energy gap 𝐸opt variation in various Er2O3content.

glassy nature. The optical band gap 𝐸opt values of the glassescan be calculated using the relation (proposed by Davis andMott) between the absorption coefficient 𝛼(𝜔) and photonenergy ℏ𝜔 of the incident radiation and are given below[19, 20]:

𝛼 (𝜔) =

𝐴 (ℏ𝜔 − 𝐸opt)𝑛

(ℏ𝜔), (3)

where 𝐸opt is the optical band gap energy in eV, 𝐴 is a con-stant, and the exponent 𝑛 takes different values dependingon themechanism of interband transitions [19].The variationof the optical energy band gap (𝐸opt) versus mol% of Er2O3is shown in Figure 5 where the optical band gap is graduallyincreased from 3.04 to 3.14 eV as the Er

2O3content is added

into the ZnO-TeO2glass system.

It should be noted however that the 𝐸opt is found to behigher than in a system with single doped Er

2O3(2.43–

2.71 eV) [5] and lower than the pure TeO2(3.97 eV). The

observed increase of the optical band gap 𝐸opt is attributedto the substitution of TeO

2by Er2O3. The addition of small

amount of rare-earth is capable of disturbing the disorderand consequently increases the optical band gap energy asshown in Table 1. Also, Figure 4 shows that several significantabsorption peaks are observed which are contributed by theexcited state of Er3+ ions.

The upconversion luminescence spectra in the rangeof 400 nm–650 nm at the excitation of 520 nm have beenobserved as shown in Figure 6. Some emission peak can beobserved where the emission band center is around 555 nmto 557 nm. It was clear that the higher mol% of erbium dopedinto the glass gives the decrease of intensity. Usually, whenthe concentration is high, the nonradiative decay processwill increase, while radiation relaxing decreases the intensityof luminescence decrease [21]. It was found that the highermole% of erbiumdoped into the glass resulted in the decreaseof the intensity due to the concentration of Er3+ that affected

4mol% Er2O3

3mol% Er2O3

2mol% Er2O3

1mol% Er2O3

0mol% Er2O3

PL in

tens

ity (a

.u.)

450

400

350

300

250

200

150

100

50

0

400 450 500 550 600 650

Wavelength (n·m)

Figure 6: A luminescence spectrum of EZT glasses.

the intensity of upconversion luminescence [22].The presentdata will be gathered with previous data on tellurite glass inorder to study the structure of these glasses [23, 24].

4. Conclusion

New tellurite glasses in the form 𝑥Er2O3-20ZnO-(80 −

𝑥)TeO2(𝑥 = 0, 1, 2, 3, and 4 mole%) (EZT) have been syn-

thesized. The glasses have the following feature due to theincrease of Er

2O3mol%:

(1) density increased from 4.22 to 4.47 g/cm3,(2) molar volume decreased from 33.08 to 32.66 cm3,(3) optical energy gap increased from 3.04 to 3.14 eV,(4) upconversion luminescence spectra showed peaks at

555 to 557 nm.

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper.

Acknowledgments

Part of this paper has been presented at the FundamentalScienceCongress 2014, August 19-20, 2014, at Universiti PutraMalaysia, Serdang. The financial support from Ministry ofScience, Technology and Innovation, Malaysia, and Univer-siti Putra Malaysia (UPM), each under the FundamentalResearch Grant Scheme (vote no. 5524288) and ResearchUniversity Grant Scheme (vote no. 9340800) is gratefullyacknowledged.

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