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Physica B 404 (2009) 3470–3474

Contents lists available at ScienceDirect

Physica B

0921-45

doi:10.1

� Corr

E-m

journal homepage: www.elsevier.com/locate/physb

Optical and FTIR properties of Se93�XZn2Te5InX chalcogenide glasses

Abhay Kumar Singh, Neearj Mehta, Kedar Singh �

Department of Physics, Banaras Hindu University, Varanasi-221005, India

a r t i c l e i n f o

Article history:

Received 6 February 2009

Received in revised form

9 May 2009

Accepted 22 May 2009

PACS:

71.23.Cq

91.60.Mk

Keywords:

Chalcogenide glasses

Optical properties

FTIR spectra

Average coordination /zS

26/$ - see front matter & 2009 Elsevier B.V. A

016/j.physb.2009.05.045

esponding author. Tel.: +91542 2307308; fax

ail address: kedar_abhay@rediffmail.com (K. S

a b s t r a c t

In this work, we report the optical properties of bulk Se93�XZn2Te5InX (X ¼ 0, 2, 4, 6 and 10)

chalcogenide glasses. Refractive index, extinction coefficient, real dielectric constant (e0), imaginary

dielectric constant (e00), absorption coefficient (a) and energy band gap were obtained from analysis of

common range (250–1100 nm) UV/Visible transmittance spectrum. Besides, transmission percentages

were obtained from FTIR spectra in wave number range 4000–400 cm�1.The concentration dependence

structural phenomena have been explained with help of average coordination /zS.

& 2009 Elsevier B.V. All rights reserved.

1. Introduction

Chalcogenide glasses have been extensively studied more thanfour decades, particularly in form of binary [1–6], ternary [7–12]and multi-components [13–18] alloys. Due to their wide rangeof commercial and technological applications, such as switchingmemory, thermal imagining, chemical, ultra-high-density phase-change storage and memory, integrated fibre optics, infraredphoto-detectors and photo-voltaics and biosensors [19–26].

It is well known that the binary and ternary chalcogenidesglasses have some significant drawbacks like low thermalstability, low crystallization temperature and aging effects. Inorder to resolve these shortcomings of binary and ternarychalcogenide glasses several investigators have reported workon quaternary (or multicomponent) alloys [13–18]. Recently,much attention is turned towards to multicomponent chalcogen-ide glasses, especially for their successful applications in ion-selective potentiometry [27,28], optical fibers [29] and opticalmemory applications [30].

Optical properties of multicomponent chalcogenide glasses arealso found great attention because of their high transmittance inIR spectral region [31] and variety of phenomena they show whenexposed to UV/Visible light or other radiation having photonenergy comparable to their optical band gap [32–34]. The variouskinds of photo-induced structural or physico-chemical changes

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ingh).

(such as photo-crystallization, photo-polymerization, photode-composition, photo-induced morphological changes, photo-vaporization, photo-dissolution) are observed in amorphouschalcogenides [35].

The IR transparency in chalcogenide glasses are usuallyreported in wave length range 1–14mm. High IR transparency ofchalcogenide glasses is useful for low material dispersion, lowlight scattering, long wavelength multi-phonon edge [36].Particularly MID-IR transparency region of chalcogenides isreceiving more attention of investigators due to useful applica-tions to detect the bimolecular changes in field of biology [37,38].

Recently, Zn and Te containing Se based multi-componentamorphous chalcogenides are identified as prospective composi-tion for investigation [27,39,40]. This also motivates us to studythe optical properties of some new quaternary chalcogenideglasses. In present research paper we have reported the opticalproperties of Se93�XZn2Te5InX chalcogenide glasses in terms ofoptical energy gap (Eg), refractive index (n), extinction coefficient(k), real dielectric constant (e0) imaginary dielectric constant (e00),absorption coefficient (a). Among these, the FTIR transmissionproperties of present glasses are also included in this study.

2. Material preparation and characterization

Bulk multicomponent glassy materials were prepared by meltquenched technique. High purity (499.999 at%) elements Sele-nium, Zinc, Tellurium and Indium were used. The desired amounts

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Fig. 1. XRD patterns of Se93�XZn2Te5InX (X ¼ 0, 2, 4, 6 and 10) chalcogenide glasses.

Fig. 2. UV/Visible spectra of Se93�XZn2Te5InX (X ¼ 0, 2, 4, 6 and 10) chalcogenide

glasses.

A. Kumar Singh et al. / Physica B 404 (2009) 3470–3474 3471

of elements were weighed by electronic balance and put intoclean quartz ampoules (length of ampoules 8 cm and diameter14 mm). The ampoules were evacuated and sealed under at avacuum of 10�5 Torr to exclude reaction of glasses with oxygen athigh temperature. The bunch of sealed ampoules was heated inelectric furnace up to 1173 K at the rate of 5–6 K/min and kept atthat temperature for 10–11 h. During the melting process theampoules were frequently rocked to ensure the homogeneity ofmolten materials. After achieving desired melting time, theampoules with molten materials were rapidly quenched into icecooled water. Then ingots of glassy materials were removed fromthe ampoules. The amorphous nature of materials was confirmedby PHILIPS XRD, as shown in Fig. 1.

For optical characrization the glassy bulk materials wereprepared in form of thin pellets under the load of 5 ton. Propercare was taken to ensure the equal thickness of pellets. UV/Visibleabsorption spectra were recorded on thin pellets by usingSHIMADZU, UV-1700 model spectrometer, in spectral range250–1100 nm. Here we have preferred thin pellet samples ratherthan films specimen because our goal was to define the bulknature of glassy materials.

FTIR measurements were performed on KBr pellets whichcontain the powder of prepared glassy materials in appropriateratio (1:50). Particular care was taken to ensure the 1:50 ratio ineach pellet. Translucent property of the pellets was recorded inwave number range 4000–400 cm�1 by Perkin Elmer, SpectrumRX-1 type spectrometer. The spectra were collected at resolutionof 4 cm�1 and each spectrum was the average of ten scans.

3. Result and discussion

Recorded UV/Visible absorption spectra of Se93�XZn2Te5InX

(X ¼ 0, 2, 4, 6 and 10) glasses are shown in Fig. 2. It is evident fromFig. 2, a sharp absorption peak lies between �250 and 400 nmwave length range with increasing absorbance. Absorbancespectra of present systems are nearly constant above the wavelength 400 nm. However, past thin films studies of multi-component chalcogenide glasses demonstrated that such typeof absorbance peak lies in the wave length range 400–700 nm[41]. In our case, the absorbance peaks are shifted towardsto lower wave length side. This absorbance peak shifting may bearises due to presence of Zn in multicomponent glassy alloys.

The average refractive index of glassy systems has beenevaluated from Kramers–Kronig relation [42], with help ofobtained absorption peak data in wave length range270–300 nm (the common maximum and minimum absorbancespectrum peak wave length range of each glassy system). Toobtain the average values of n, the integration limits of appro-priate segments for Kramers–Kronig relation were fixed withinrange of used data to average of n. The refractive index is variedsignificantly with composition of glasses, as listed in Table 1. It isclear from Table 1 that the refractive index is maximum for 6 at%of In.

The average extinction coefficient of systems is evaluated fromSwanepoel [43] relation:

k ¼ al=ð4pÞ¼ l=ð4pdÞflnðwÞ � 100g

Here d is the thickness of the pellets, a is the absorptioncoefficient and w is absorbance of band tail. The average extinctioncoefficients of present glasses were obtained in above saidabsorbance peak observed in wave length range 270–300 nm bysum of total K values dividing by total number of used data pointsof each glassy alloy. The variation of average extinction coefficientwith indium atomic percentage is listed in Table 1. It is also foundmaximum at 6 at% of In.

The relative permittivity of incident light for optical materialsis key parameter to determine their real (e0) and imaginary (e00)dielectrics constants. These two optical parameters of glassysystems are evaluated with help of average refractive index n andaverage extinction coefficient k [44] by using the followingrelations:

�0 ¼ n2 � k2

and

�00 ¼ 2nk

The variation of real and imaginary optical dielectric constantswith Indium concentration is also shown in Table 1. The obtainvalues of e0 and e00 are also maximum at 6 at% of In.

The absorption coefficient a describes the extent to which theintensity of the optical beam of particular spectral range isreduced as it passes through a specific material. The absorptioncoefficient of glassy systems has been calculated from well knownrelation [45]:

a ¼ 4pk=l.

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Table 1Obtained average values of extinction coefficient (K), refractive index (n), real dielectric constant (e0), imaginary dielectric constant (e00), optical energy band gap E (eV) and

average coordination number /rS.

Samples Average (K) Refractive index

(n)

Real dielectric

constant (e0)Imaginary dielectric

constant (e00)Energy band gap E

(eV)

Average /rS

Se93Zn2Te5 2.89�10�3 3.10 9.609 1.789�10�2 3.65 2.05

Se91Zn2Te5In2 3.35�10�3 3.12 9.733 2.089�10�2 3.46 2.07

Se89Zn2Te5In4 3.99�10�3 3.33 11.087 2.658�10�2 3.1 2.09

Se87Zn2Te5In6 5.05�10�3 3.58 12.815 3.612�10�2 2.8 2.11

Se83Zn2Te5In10 3.74�10�3 3.20 10.239 2.39�10�2 3.23 2.15

Fig. 3. Plot of absorption coefficient vs energy.

Fig. 4. Plot of (ahn)1/2 vs energy.

A. Kumar Singh et al. / Physica B 404 (2009) 3470–34743472

Plots of absorption coefficient (a) as function of respective photonenergy are shown in Fig. 3. The composition dependenceof absorption coefficient also shows a reversal trend at 6 at% ofIn. The optical energy band gap of glassy systems is obtained withhelp of evaluated values of absorption coefficient (a) by usingTauc relation [46,47]:

ðahvÞ1=2¼ ðhv� EgÞ

Plots of (a hn)1/2 vs photon energy (hn) for Se93�XZn2Te5InX glassesare shown in Fig. 4. Value of indirect optical energy band gap isdetermined from the plots of (a hn)1/2 vs photon energy (hn).The variation of optical energy band gap (Eg) with correspondingindium concentration of the systems is shown in Table 1. FromTable 1, it is evident that the, optical energy band gap is minimumat 6 at% of In.

Many approaches have been proposed to explain the composi-tion dependence of physical properties of chalcogenide glasses[48–56]. One of these approaches is the so called chemicallyordered network model (CONM) [48–51], in which the formationof hetero-polar bonds is favored over the formation of homo-polar bonds. In this model, the glass structure is assumed to becomposed of cross-linked structural units of the stable chemicalcompounds (hetero-polar bonds) of the system and excess, if any,of the elements (homo-polar bonds). Due to chemical ordering,features (such as extremum, a change in slope or kink) occur forthe various properties at the so-called tie line or stoichiometriccompositions at which the glass structure is made up of cross-linked structural units consisting of hetero-polar bonds only.The tie line compositions, where the features seen have chemicalorigin are also referred as the chemical threshold of the system[57,58]. Other approaches are the so-called topological models,

which are based on the constraint theory [52–55] and on thestructural dimensionality considerations [56]. In these models,the properties can be discussed in terms of the averagecoordination number (/zS), which is indiscriminate of the speciesor valence bond. In the constraints model [52–55], by equatingthe number of operating constraints to the number of degrees offreedom, /zS of the most stable glass is shown to be �2.4. At thisvalue of /zS, the glass network changes from an elastically floppy(polymeric glass) type to a rigid (amorphous solid) type. Byextension of the topological model to the medium-range struc-tures, other features at /zS–2.67 have also been observed [48].However, the features observed at /zS–2.67 were attributed to achange from two-dimensional layered structure to a three-dimensional network arrangement due to cross-link.

In the present case, the value of /zS varies between 2.05and 2.15, as listed in Table 1. The reversal in increasing ordecreasing trend of different optical parameters is observed at/zS ¼ 2.11, which is smaller than the first threshold values/zS ¼ 2.4. This may be due to the fact that the applicabilityof above topological models has been generally verified for binaryand ternary systems of chalcogenides. For quaternary alloys,the mechanical stabilized structure can therefore be observedat lower value of average coordination number. Recently someauthors reported the reversal in increasing or decreasingtrend of different physical properties of some binary alloys ofchalcogenide glasses at lower value of average coordinationnumber [59–61].

FTIR spectrum transmission percentage of Se93�XZn2Te5InX

(X ¼ 0, 2, 4, 6 and 10) chalcogenide glasses are shown in Fig. 5(a–e). The FTIR spectrum of glassy systems exhibits enhancedMID-IR property with increasing transmission percentage up to

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Fig. 5. (a–e) FTIR transmission spectra of Se93�XZn2Te5InX (X ¼ 0, 2, 4, 6 and 10) glasses.

A. Kumar Singh et al. / Physica B 404 (2009) 3470–3474 3473

threshold (6 at% of In) Indium concentration. Although FTIRspectra of Se89Zn2Te5In4 and Se87Zn2Te5In6 show someabsorption peaks in MID-IR region, but their relativetransmission percentage is much higher than the other glassysystems. These absorption peaks may be arise due to presence ofH2O and other impurity content in glassy samples. However, nosuch types of absorption peaks are observed in remaining threeglassy systems. Such broad MID-IR transmission spectrum inSe93�XZn2Te5InX chalcogenide systems arises due to collectivemulti-phonon excitation. It is also reported in past [62,63], themulti-phonon excitation of chalcogenide glasses also dependson defects of the system localized states. It may be accountedfor by greater MID-IR transmission percentage of Se89Zn2Te5In4

and Se87Zn2Te5In6 alloys as compared to other three glasses. The

optical and FTIR characterization of present glasses indicates thatSe87Zn2Te5In6 alloy is most suitable composition of this series.

4. Conclusion

UV/Visible and FTIR characterization of Se93�XZn2Te5InX (X ¼ 0,2, 4, 6 and 10) alloys leads to the following conclusions:

(a)

The optical parameters like optical refractive index (n),extinction coefficient (k), real dielectric constant (e0) imagin-ary dielectric constant (e00), absorption coefficient (a) havemaximum for Se87Zn2Te5In6 glass, while energy band gap hasminimum for this composition.

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A. Kumar Singh et al. / Physica B 404 (2009) 3470–34743474

(b)

The FTIR transmission percentage is also greater for Se87Zn2-

Te5In6, at the average coordination number /zS ¼ 2.11.

(c) The major conclusion is that the Se87Zn2Te5In6 is most

suitable glass of this series for prospective uses.

Acknowledgments

Authors are thankful to University Grants Commission (UGC),New Delhi for providing financial support to carry out researchwork (UGC Proj.33-40/2007 SR). We are also deeply thankful toProf. O.N. Srivastava who helped us in various ways in the courseof this study.

References

[1] A.A. El-Fadl, M.M. Hafiz, M.M. Wakaad, A.S. Ashour, Physica B 398 (2007) 118.[2] K. Singh, A.K. Singh, N.S. Saxena, Curr. Appl. Phys. 8 (2008) 159.[3] A.K. Singh, K. Singh, J. Optoelectron. Adv. Mater. 9 (2007) 3756.[4] A.S. Maan, D.R. Goyal, J. Ovonic.Res. 3 (2007) 45.[5] N. Mehta, A. Kumar, J. Therm. Anal. Calorimetry 87 (2007) 343.[6] A.K. Galwey, J. Therm. Anal. Calorimetry 82 (2005) 423.[7] S. Srivastava, N. Mehta, C.P. Singh, R.K. Sukla, A. Kumar, Physica B 403 (2008) 2910.[8] S. Gu, Z. Ma, H. Tao, C. Lin, H. Hu, X. Zhaoa, Y. Gong, J. Phys. Chem. Solids 69

(2008) 7.[9] S.M. El-Sayed, Appl. Surface Sci. 253 (2007) 7089.

[10] K.A. Varshneya, J.M. Daniel, J. Non-Cryst. Solids 353 (2007) 1291.[11] K.N. Michael, M. Maria, J. Non-Cryst. Solids 352 (2006) 567.[12] E.R. Shaaban, Physica B 373 (2006) 211.[13] H. Guo, Y. Zhai, T. Haizheng, G. Yueqiu, X. Zhao, Mater. Res. Bull. 42 (2007)

1111.[14] S. Boycheva, V. Vassilev, J. Optoelectron. Adv. Mater. 4 (2002) 33.[15] Z.G. Ivanova, E. Cernoskova, V.S. Vassilev, S.V. Boycheva, Mater. Lett. 57 (2003)

1025.[16] V.S. Vassilev, S.H. Hadjinikolova, S.V. Boycheva, Sensors Actuators B 106

(2005) 401.[17] Y. Xu, Q. Zhang, W. Wang, H. Zeng, L. Xu, G. Chen, Chem. Phys. Lett. 462 (2008) 69.[18] J. Troles, Y. Niu, D.C. Arfuso, F. Smektala, L. Brilland, V. Nazabal, V. Moizan,

F. Desevedavy, P. Houizot, Mater. Res. Bull. 43 (2008) 976.[19] H.F. Hamann, O.M. Boyle, Y.C. Martin, M. Rooks, H.K. Wickramasinghe, Nat.

Mater. 5 (2006) 83.[20] M. Bayindir, O. Shapira, D.S. Hinczewski, J. Viens, A.F. Abouraddy,

J.D. Joannopoulos, Y. Fink, Nat. Mater. 4 (2005) 820.[21] S.A. Mcdonald, G. Konstantatos, S. Zhang, P.W. Cyr, E.J.D. Klem, L. Levina,

W.H. Sargent, Nat. Mater. 4 (2005) 138.[22] H. Fritzsche, J. Phys. Chem. Solids 68 (2007) 878.[23] V. Balitska, O. Shpotyuk, H. Altenburg, J. Non-Cryst. Solids 352 (2006) 4809.[24] A. Ganjoo, H. Jain, C. Yu, R. Song, J.V. Ryan, J. Irudayaraj, Y.J. Ding, C.G. Pantano,

J. Non-Cryst. Solids 352 (2006) 584.[25] G. Boudebs, S. Cherukulappurath, M. Guignard, J. Troles, F. Smektala,

F. Sanchez, Opt. Commun. 230 (2004) 331.

[26] P. Pattanayak, S. Asokan, Europhys. Lett. 75 (2006) 778.[27] E. Pungor, J. Anal. Chem. 357 (1997) 184.[28] P. Demarco, B. Pejcic, Anal. Chem. 72 (1999) 669.[29] J. Kobelke, J. Kirshhof, S. Scheffer, A. Schuwuchow, J. Non-Cryst. Solids

256–257 (1999) 226.[30] G. Zhang, D. Gu, X. Jiang, Q. Chen, F. Gan, Appl. Phys. A Mater. Sci. Process. 80

(2005) 1039.[31] A.V. Kolobov, J. Tominaya, J. Optoelectron. Adv. Mater. 4 (2002) 679.[32] S.R. Elliott, Physics of Amorphous Materials, Longman, New York, 1990.[33] M. Lain, A.B. Seddon, J. Non-Cryst. Solids 184 (1995) 30.[34] A.B. Seddon, J. Non-Cryst. Solids 184 (1995) 44.[35] P.J.S. Ewen, A.E. Owen, High-Performance Glasses, Blackie, London, 1992.[36] S.M. El-Sayed, Semicond. Sci. Technol. 18 (2003) 337.[37] J. Keirsse, C.B. Pledel, O. Loreal, O. Sire, B. Bureau, P. Leroyer, B. Turlin, J. Lucas,

Vibr. Spectrosc. 32 (2003) 23.[38] T.S. Kavetskii, V.D. Pamukchieva, O.I. Shpotyuk, J. Appl. Spectrosc. 67 (2000)

687.[39] S.V. Boycheva, V.S. Vassilev, Z.G. Ivanova, J. Appl. Electrochem. 32 (2002) 281.[40] V.S. Vassilev, S.H. Hadjinikolova, S.V. Boycheva, Sensors Actuators B 106

(2005) 401.[41] A.K. Singh, K. Singh, J. Mod. Opt. 56 (2009) 471.[42] A. Anedda, C.M. Carbonaro, A. Serpi, N. Chiodini, A. Paleari, R. Scott,

G. Brambilla, V. Pruneri, J. Non-Cryst. Solids 280 (2001) 287.[43] R. Swanepoel, J. Phys. E Sci. Instrum. 17 (1984) 896.[44] V. Pandey, S.K. Tripathi, A. Kumar, Physica B 388 (2007) 200.[45] S. Srivastava, V. Pandey, S.K. Tripathia, R.K. Shukla, A. Kumar, J. Ovonic Res. 4

(2008) 83.[46] J. Tauc, in: J. Tauc (Ed.), Amorphous and Liquid Semiconductors, Plenum Press,

New York, 1979, p. 159.[47] F. Urbach, Phys. Rev. 92 (1953) 1324.[48] G. Lucovsky, F.L. Galeener, R.H. Geils, R.C. Keezer, in: P.H. Gaskell (Ed.),

The Structure of Non-Crystalline Materials, Taylor and Francis, London, 1977,p. 127.

[49] G. Lucovsky, R.J. Nemanich, F.L. Galeener, in: W. Spear (Ed.), Proceedings ofSeventh International Conference on Amorphous Liquid Semiconductors,Center for Industrial Consultancy and Liaison, University of Edinburgh,Edinburgh, 1977, p. 130.

[50] F. Betts, A. Bienesock, S.R. Ovshinsky, J. Non-Cryst. Solids 4 (1970) 554.[51] G. Lucovsky, F.L. Galeener, R.C. Keezer, R.H. Geils, H.A. Six, Phys. Rev. B 10

(1974) 5134.[52] J.C. Phillips, J. Non-Cryst. Solids 34 (1979) 153.[53] J.C. Phillips, J. Non-Cryst. Solids 57 (1983) 355.[54] J.C. Phillips, M.F. Thorpe, Solid State Commun. 53 (1985) 699.[55] K. Tanaka, Phys. Rev. B 39 (1989) 1270.[56] C.H. Hurst, E.A. Davis, in: W. Brenig (Ed.), Proceedings of Fifth International

Conference on Amorphous and Liquid Semiconductors, Taylor and Francis,London, 1974, p. 349.

[57] P. Boolchand, Key Eng. Mater. 13–15 (1987) 131.[58] S. Mahadevan, A. Giridhar, J. Non-Cryst. Solids 110 (1989) 118.[59] S.U. Nemilov, Sov. J. Phys. Chem. 37 (1964) 1026.[60] A. Feltz, Amorphous Inorganic Materials and Glasses, VCH, Weinheim, 1993.[61] Z.U. Borisova, Glassy Semiconductors, Plenum, New York, 1981.[62] S.M. El-Sayed, Semicond. Sci. Technol. 18 (2003) 337.[63] T.S. Kavetskii, V.D. Pamukchieva, O.I. Shpotyuk, J. Appl. Spectrosc. 67 (2000)

687.