Efi

Aa

b

c

a

ARA

KOCXSP

1

tltvpeodomasaSsb

amp

0d

Optik 123 (2012) 1133– 1137

Contents lists available at ScienceDirect

Optik

jou rna l homepage: www.elsev ier .de / i j leo

ffect of NaF on optical and structural properties of CdxZn1−xS nano crystallinelms

yush Kharea,∗, R.B. Sahub, Suchinder K. Sharmac

Department of Physics, National Institute of Technology, Raipur 492 010, IndiaDepartment of Physics, Govt. College of Science, Raipur 492 010, IndiaLuminescence Laboratory, Geo Sciences Division, Physical Research Laboratory, Ahmedabad 09, India

r t i c l e i n f o

rticle history:eceived 16 February 2011ccepted 12 July 2011

eywords:

a b s t r a c t

This work investigates the effect of NaF on optical and structural properties of nano crystalline CdxZn1−xSfilms. The CdxZn1−xS films are prepared through chemical bath deposition (CBD) technique in aque-ous alkaline bath and their subsequent condensation on substrates. The as-obtained samples arecharacterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–VIS absorptionspectroscopy. Micro structural features, obtained from XRD analysis confirm the formation of cubic phase

ptical propertieshemical bath depositionRDEMhotoluminescence

of undoped as well as NaF doped CdxZn1−xS nano particles while SEM observations depict non-uniformdistribution of grains. These results show the average grain size of pure as well as NaF doped samples torange from 50 to 90 nm. Tauc’s plots, extracted from absorption spectra exhibit absorption to be domi-nating mainly in blue-green region of visible spectrum. The room-temperature photoluminescence (PL)spectra of CdxZn1−xS samples show a peak around 425 nm, which gets blue shifted for doped sampleindicating improvement in PL properties on its addition.

. Introduction

Nano structured materials [1–4] are of deep interest becausehey bridge the gap between the bulk and molecular levels andead to entirely new avenues for applications, especially in elec-ronics, opto-electronics and biology. A solid exhibiting a distinctariation in optical and electronic properties with a variation ofarticle size less than 100 nm, is called a nano structure and is cat-gorized as (i) two dimensional, e.g. thin films or quantum well, (ii)ne dimensional, e.g. quantum wires and (iii) zero-dimensional orots. These nano particles are capable of displaying novel electro-ptical, magnetic, chemical and structural properties, which findany important technological applications [5]. An extremely active

nd prolific field in nano-materials is finding ways to controlize and morphology of the nano particles as their propertiesnd applications are largely dependent on size and morphology.uch properties make semiconducting nano structures suitable foreveral kinds of applications from anti-reflecting coatings [6] toioelectronics [7] and light-emitting devices [8].

II–VI semiconductor nano crystals (quantum dots), whose radii

re smaller than bulk exiton constitute a section of materials inter-ediate between molecular and bulk forms of matter. The optical

roperties of these materials depend strongly on the size and

∗ Corresponding author. Tel.: +91 771 2254199; fax: +91 771 2254600.E-mail address: akhare.phy@nitrr.ac.in (A. Khare).

030-4026/$ – see front matter © 2011 Elsevier GmbH. All rights reserved.oi:10.1016/j.ijleo.2011.07.039

© 2011 Elsevier GmbH. All rights reserved.

surface quality, which are improved by passivating the bare surfacewith a suitable coating on shell material [9]. Quantum confine-ment of the electron-hole pair leads to an increase in the effectiveband-gap with decreasing crystallite size [10]. A similar relation-ship has been deduced for nano structures prepared from the directband-gap semiconductors, e.g. ZnS, CdS, PbS. These semiconductornano particles exhibit satisfactory PL and electroluminescent (EL)properties and offer promising applications in the field of opto-electronics.

In the family of II–VI semiconductors, ZnS (Eg = 3.7 eV) is theforemost and commercially important candidate because of itsfavourable electronic and optical properties for opto-electronicapplications especially in nano crystalline form [11–13]. On theother hand CdS (Eg = 2.42 eV), used as counterpart of ZnS formany years, is one of the first discovered semiconductors. CdSfinds promising applications in photochemical catalysis, gas sensordetectors for laser and infrared solar cells, nonlinear optical materi-als, various luminescence and opto-electronic devices [14–16]. It iswell established that CdxZn1−xS films possess properties betweenthose of CdS and ZnS [17,18]. Since their addition produces a com-mon lattice in which band structure has a larger band-gap thanCdS, it makes the material more attractive for fabricating variousdevices. Recently Khare [19–21] has reported various results on

electro-optical and characteristic properties of CdxZn1−xS films. Theluminescent emission and efficiency of semi conducting devicesare strongly dependent on the concentrations and characteristicsof the dopant material. These properties are identified as one of

1 ik 123 (2012) 1133– 1137

tsbsatb[epbSttcmp

ttpttoRbp

2

2

mbibaat3IotTaacfivtsiawbpfg[2mwa

134 A. Khare et al. / Opt

he most important techniques to reveal the energy structure andurface states of the particles [22]. Localized trap-states inside theand-gap were studied by Denzler [23] in detail to recognize theub band-gap energy levels. It was found that the defect levels playn important role in determining luminescence characteristics ofhe ZnS nano particles [24] and mass of the nanoparticles exhibitroad luminescence arising from the deep traps of the surface states25]. Hence to understand its mechanism, it becomes important toxtend investigations to find the role of dopant on electro-opticalroperties. Role of NaF in photo conducting CdS powders, preparedy firing at 500 ◦C for 1 h, is found to be two-fold by Bhushan andharma [26,27]: (i) it acts as a flux because impurities added cannoturn effective in its absence and (ii) it acts as dopant since at its par-icular concentration the highest photo response is noticed. Theseonclusions are based on the measurements made by Flame Photo-etric and Spands methods. NaF also acts as an agent in reducing

article size and compensating charge.Taking into consideration the improvement in photocurrent in

he presence of NaF, present paper reports the results of investiga-ion on effects of NaF concentration on the structural and opticalroperties of CdxZn1−xS nano sized films prepared through CBDechnique (chemical growth at low temperature) [28]. The CBDechnique is considered to be an inexpensive, simple and capablef depositing optically smooth, uniform, and homogeneous layers.ecently there is a new interest in the CBD, which is motivatedy its successful use in depositing buffer layers of CdS in thin-filmhotovoltaic cells based on CdTe and CuInSe2 [29].

. Experimental techniques

.1. Sample preparation

The films are grown through vertically dipping the commerciallyicroscopic glass slides of dimension 75 × 24 × 2 mm in a chemical

ath for 60 min. The substrates are cleaned thoroughly by ultrason-cation using a standard procedure before immersing in chemicalath. The solution is prepared using 1 M solutions of highly purend analytical reagent grade zinc acetate [Zn (CH3COO)2], cadmiumcetate [Cd (CH3COO)2] (zinc acetate + cadmium acetate = 7.00 ml),hiourea [SC(NH2)2], triethanolamine (HOCH2CH2)3N (TEA) and0% aqueous ammonium hydroxide (NH4OH) (mixture’s pH ≈ 11).

n addition, appropriate amount of 0.01 M solution of sodium flu-ride (NaF) is also added to the original mixture. Thiourea andriethanolamine are two commonly used sulphiding agents [30].riethanolamine is used as a complexing agent and pH balancerlso. The temperature of reaction mixture is maintained at thepproximate temperature of 60 ◦C. In the beginning, when pre-ipitation starts, the solution is stirred for few minutes and nourther stirring is done during the deposition. After that depositions made in the static condition by placing glass substrates inclinedertically to the walls of the beaker until solution reaches desiredemperature. The technique under these conditions relies on thelow release of S−2 ions to an alkaline solution in which the metalon is buffered at a low concentration. Thereafter, the substratesre removed from the beaker and treated with distilled water toash out the uneven overgrowth of grains at the surface and dried

y keeping in open atmosphere under sun light until it dries com-letely. This helps in achieving adequate operating life of PL cellabricated with such film. The dried films are quite adherent to thelass substrate surface and are irremovable. Bhushan and Chandra31] reported that films prepared through CBD last for more than

years. The thickness of the film is measured by interferometryethod and is found to lie between 1 and 2 �m. The dipping timeas taken as 1 h because it gave optimum PL intensity, uniformity

nd uniform thickness of deposited films.

Fig. 1. (a) X-ray diffractograms of (Cd0.7–Zn0.3)S film and (b) X-ray diffractogramsof (Cd0.7–Zn0.3)S: NaF film.

2.2. Measurement details

The optical absorption spectra are recorded with a Varian(UV-VIS) DMS-100 spectrophotometer in the wavelength range400–700 nm. The various X-ray analyses were done at RSIC, Nag-pur using a computerized Philips diffractometer with Cu/K-alpharadiations while SEM studies were performed at BSIP, Lucknowusing a LEO (430) scanning electron microscope. The PL excitationsource was a high pressure mercury source, from which 365 nmradiations were selected with Carl-Zeiss interference filter. The PLemissions were observed with the help of Thermo-Jarrel Ash grat-ing monochromator, an RCA-6217 photomultiplier tube (PMT) anda sensitive nano ammeter.

3. Results and discussions

3.1. Structural studies

3.1.1. XRD resultsX-ray diffractograms compared with standard JCPDS files are

analyzed and reported. The X-ray diffractograms of pure and NaFdoped (Cd0.7–Zn0.3)S films at RT are presented in Fig. 1. Thesediffractograms exhibit polycrystalline nature with an extraordinarybroadening in the peaks. This may be attributed either to the sizedistribution of the nanocrystallites deposited on the glass slide orinvolvement of certain kinds of lattice imperfections like stackingfault [32]. Prominent diffraction lines of CdS, seen in these patternsare indexed as (1 1 1)c and (2 2 0)c planes indicating the formation ofa cubic phase. In the NaF doped sample one new peak correspond-ing to CdS [(3 1 1)c] is seen. The traces of other phases are negligiblysmall. The inter planner spacing ‘d’ of the peaks calculated fromthe 2� values of the diffraction lines, are listed in Table 1. The mainpeak of XRD pattern for pure and NaF doped (Cd0.7–Zn0.3)S filmsis located around 2� = 26.5◦. Other two peaks are corresponding to2� = 43.5◦ and 52.5◦. These patterns of pure and NaF doped sam-ples are in good agreement with the reported data of CdS and ZnSfilms. The assignment of diffraction lines is made by comparingwith JCPDS files of ZnS and CdS (cubic, JCPDS 10-454) and the eval-uated and reported values of parameters like lattice interval, lattice

constant and Miller indices (Table 1). The XRD peaks are fairly broadsuggesting the nano structure of pure and NaF doped (Cd0.7–Zn0.3)Ssamples. This good agreement between the observed ‘d’ values andreported data suggests the suitability of the crystal structures and

A. Khare et al. / Optik 123 (2012) 1133– 1137 1135

Table 1Observed and reported XRD data of (Cd0.7–Zn0.3)S films. Preparation temperature: 60 ◦C, time of deposition: 1 h.

System d values (A) Miller indices h k l Intensity Lattice constant (A)

Obs. Rep. Obs. Rep. Obs. Rep.

(Cd0.7–Zn0.3)S 3.34 3.36 (1 1 1)c 42 100 5.779 5.822.04 2.058 (2 2 0)c 12 80 5.794 5.82

58 100 5.739 5.8212 80 5.829 5.8215 60 5.875 5.82

ut[e[

d

wat(

ostpaabagsd

3

NFmaspsmNr

3.2.1. Absorption spectraThe study of optical absorption is important in understand-

ing the behavior of semiconductor nano crystals. A fundamental

0

0.5

1

1.5

2

2.5

3

3.5

4

700650600550500450400

Wavelength (nm)

a

Abs

orpt

ion

(Cd0.7–Zn0.3)S: 3.3135 3.36 (1 1 1)c

NaF 2.0560 2.058 (2 2 0)c

1.7670 1.753 (3 1 1)c

nit cell parameters. From the table, it is concluded that basic struc-ure of the compound remains unaltered in the presence of dopant33]. If there is no inhomogeneous strain, the crystallite size “d” isstimated from the peak width with the Debye–Scherrer’s formula34,35]:

= 0.9�

cos �(1)

here � is the wavelength of X-ray radiations, the full widtht half maxima (FWHM) of the peak and � is the angle of diffrac-ion. The estimated average particle size for pure and NaF dopedCd0.7–Zn0.3)S samples is found to lie in the 90 nm range.

The broadening of XRD lines is associated to small particle sizef coherently diffracting crystallites or strains present within theamples or both. Small crystallites have relatively low lattice planeshat contribute to the broadening of different lines. Broadening ofeaks results due to micro straining of the crystal structure also, thisrises from defects like dislocation and twinning [36]. These defectsre considered to be associated with the chemically deposited filmsecause they grow spontaneously during chemical reaction [37]. As

result the chemical legends get negligible time to reach an ener-etically favourable site. Information about the strain and particleize is obtained from the full width at half maxima (FWHM) of theifferent peaks.

.1.2. SEM studiesThe SEM micrographs of (Cd0.7–Zn0.3)S and (Cd0.7–Zn0.3)S,

aF films (at a magnification of 5k and 10k) are presented inigs. 2 and 3 respectively. These compositions correspond to opti-um PL response. The as-deposited film appears to be less occupied

nd composed of largely “U” shaped grains while in NaF dopedample (Fig. 3), addition of NaF leads to great reduction in thearticle size. In this micrograph nano wire type structures areeen with diameter ∼50 nm. The observed difference between the

icrostructures of Figs. 2 and 3 is attributed to the addition ofaF. On addition of NaF, vacant spaces existing earlier are occupied

esulting in more compact structure.

Fig. 2. SEM micrographs of (Cd0.7–Zn0.3)S film (magnification = 5k).

Fig. 3. SEM micrographs of (Cd0.7–Zn0.3)S: NaF film (magnification = 10k).

3.2. Optical and electronic characterization

b

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

700650600550500450400

Wavelength (nm)

Abs

orpt

ion

Fig. 4. (a) Absorption spectrum of (Cd0.7–Zn0.3)S film and (b) absorption spectrumof (Cd0.7–Zn0.3)S: NaF film.

1136 A. Khare et al. / Optik 123 (2012) 1133– 1137

0

20

40

60

80

100

120

3.22.82.421.6

hνν (eV)

a

b

hνν (eV)

(α. h

ν)2

(α. h

ν)2 (

Arb

. uni

t)

0

20

40

60

80

100

120

3.22.82.421.6

F(f

pbOal

saa

Table 2Band gap values of different films from absorption spectra. Preparation temperature:60 ◦C, time of deposition: 1 h.

System Band gap (eV)

CdS 2.44(Cd –Zn )S 2.57

ig. 5. (a) Plot for (˛h�)2 as a function of incident photon energy h� for pureCd0.7–Zn0.3)S film and (b) plot for (˛h�)2 as a function of incident photon energy h�or NaF doped (Cd0.7–Zn0.3)S film.

roperty of semiconductors is band-gap energy separationetween the filled valence band and the empty conduction band.ptical excitations of electrons across the band-gap are stronglyllowed, producing an abrupt increase in absorption at the wave-ength corresponding to the band-gap energy.

Optical (UV-VIS) absorption measurements for nano crystallineamples are illustrated in the wavelength range 400–700 nm. Thebsorption spectra of (Cd0.7–Zn0.3)S and (Cd0.7–Zn0.3)S: NaF filmsre presented in Fig. 4. For pure sample the curve is smooth whereas

0

20

40

60

80

100

120

600550500450400350300

Wavelength (nm)

PL In

tens

ity (A

rb. U

nit)

Fig. 6. PL spectra of (Cd0.7–Zn0.3)S (�) and (Cd0.7–Zn0.3)S: NaF (�) films.

0.7 0.3

(Cd0.7–Zn0.3)S: NaF 2.36

it is quite sharp for doped one. Absorption mostly takes place inblue-green part of visible spectrum. The plots between h� and(˛h�)2 for different films are shown in Fig. 5. For allowed direct tran-sition one can plot (˛h�)2 vs h� and extrapolate the linear portionof it to a = 0 value to obtain the corresponding band-gap value. Thelinear dependence of ˛2 on h� is an indicative of direct band-gapcharacteristics of the materials. The optical band-gap Eg is relatedto the absorption coefficient by Tauc’s relation [38]. Accordingto the Tauc’s relationship, the absorption coefficient (˛) for directband-gap materials is given by:

˛(h�) = (h� − Eg)1/2 (2)

where ‘h�’ is the photon energy, the absorption coefficient andEg the band-gap value. The derived values of band-gap are com-piled in Table 2. Quantum size effects on electronic energy bandsof semiconductors become prominent when the size of nano crys-tallites is less than bulk exciton Bohr radius. Coulomb interactionbetween hole and electron plays a crucial role in nano sized solids.The quantum confinement of charge carriers modifies valence andconduction bands of semiconductors.

3.2.2. Photoluminescence spectraThe PL spectrum of semiconductor material can yield important

information on the quality and composition. Such PL spectra of pureand NaF doped (Cd0.7–Zn0.3)S films, recorded at RT are presentedin Fig. 6. These spectra consist of a broad emission band centred at425 and 410 nm respectively. As the peak energies are less than theenergy gap (Eg), these bands can be definitely identical with transi-tions involving donors, acceptors, free electrons and holes [39]. It isalso noticed that PL spectrum of doped sample has slightly greaterintensity as compared to that of undoped one and the observedshift in peak position is probably due to the availability of very lessPL centres of Cd2+. Its reason is understood on the basis of SEMmicrographs of the corresponding samples. In doped sample thevacancies existing earlier are now occupied which results in moreelectronic transitions and lead to greater PL intensity. Xu et al. [40]studied the effect of fluxes on optical properties of phosphors andfound NaF to exhibit the strongest emission as compared to otheralkali fluorides. This blue shift of PL spectrum is probably due to thestructural effect [41].

4. Conclusions

NaF doped CdxZn1−xS films are prepared through CBD tech-nique, which is a simple and suitable method for obtaining smooth,uniform, high reflecting and strong adherent thin films. XRDpatterns of the complexes reveal the particles to possess polycrys-talline cubic structures along with different prominent diffractionlines corresponding to CdS. SEM micrographs exhibit more ordereddistribution of grains in doped sample having an appearance ofleafy type structure. From these studies the average crystallite size

is estimated to lie in the 50–90 nm range. Results of absorptionspectra show a little decrease in band-gap value upon addition ofNaF. PL spectra exhibit increase in peak intensity upon doping.

ik 123

A

LsFSc

R

[[

[

[

[

[

[[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

A. Khare et al. / Opt

cknowledgements

We gratefully acknowledge Dr. R.K. Kar (Ex. Dy. Director) of BSIP,ucknow for SEM studies and Mr. S.C. Rao of RSIC, Nagpur for XRDtudies. One of the authors (A.K.) expresses his gratitude towardsaculty Members of School of Studies in Physics, Pt. Ravishankarhukla University, Raipur for their valuable suggestions and timelyooperation.

eferences

[1] D. Bera, S.C. Kuiry, S. Seal, Using template-assisted electrodeposition to synthe-size nanostructured materials, JOM 56 (2004) 49–53.

[2] A. Henglein, Small-particle research: physicochemical properties of extremelysmall colloidal metal and semiconductor particles, Chem. Rev. 89 (8) (1989)1861–1873.

[3] S. Kuchibhatla, A.S. Karakoti, D. Bera, S.S. Seal, One dimensional nanostructuredmaterials, Prog. Mater. Sci. 52 (2007) 699–913.

[4] T. Trindade, P. O’Brien, N.L. Pickett, Nanocrystalline semiconductors: synthesis,properties, and perspectives, Chem. Mater. 13 (2001) 3843–3858.

[5] J.M. Bruchez, M. Moronne, S. Weiss, A.P. Alivisatos, Semiconductor nanocrystalsas fluorescent biological labels, Science 281 (1998) 2013–2016.

[6] M.A. García, E. Borsella, S.E. Paje, J. Llopis, M.A. Villegas, R. Polloni, Lumines-cence time decay from Cu+ ions in sol–gel silica coatings, J. Lumin. 93 (2001)253–259.

[7] I. Willner, R. Baron, B. Willner, Integrated nanoparticle biomolecule systemsfor bio sensing and bio electronics, Biosensors Bioelectron. 22 (9–10) (2007)1841–1852.

[8] E.M. Drobyshevski, In searches of daemons, Phys. Atom. Nuclei 63 (6) (2000)1037–1041.

[9] J. Wang, Y. Long, Y. Zhang, X. Zhong, L. Zhu, Preparation of highly lumines-cent CdTe/CdS core/shell quantum dots, Chem. Phys. Chem. 10 (4) (2009)680–685.

10] J. Martin, F. Cichos, C. Von Borczyskowski, J. Lumin. 108 (1–4) (2004) 47.11] K. Autumn, Adhesive force of a single gecko foot-hair, Nature 405 (6787) (2000)

681–685.12] T. Matsunaga, Y. Okamura, T. Tanaka, Biotechnological applications of nano-

scale engineered bacterial magnetic particles, J. Mater. Chem. 14 (2004) 2099.13] Z.W. Pan, Z. Dai, Z.L. Wang, Nanobelts of semiconducting oxides, Science 291

(5510) (2001) 1947–1949.14] R. Agrawal, C. Barrelet, C.M. Lieber, Lasing in single cadmium sulfide nanowire

optical cavities, Nano Lett. 5 (5) (2005) 917–920.15] J.S. Jie, w.J. Zhang, Y. Jiang, X.M. Merag, Y.Q. Li, S.T. Lee, Photoconductive char-

acteristics of single-crystal CdS nanoribbons, Nano Lett. 6 (2006) 1887–1892.16] R. Ma, L. Dai, G. Qin, Nano Lett. 7 (2007) 868.

17] A. Banerjee, P. Nath, V.D. Vankar, K.L. Chopra, Properties of ZnxCd1−xS films

prepared by solution spray technique, Phy. Stat. Sol. A 46 (2) (2006) 723–728.18] R. Xie, U. Kolb, J. Li, T. Basche, A. Mews, Synthesis and characterization of

highly luminescent CdSe−core CdS/Zn0.5Cd0.5S/ZnS multishell nanocrystals, J.Am. Chem. Soc. 127 (20) (2005) 7480–7488.

[

[

(2012) 1133– 1137 1137

19] A. Khare, Characterization of chemically deposited (Zn-Cd)S: Cu nano crys-talline films, J. Optoelec. Adv. Mater. 11 (11) (2009) 1805–1809.

20] A. Khare, Effects of the zn concentration on electro-optical properties ofZnxCd1−xS films, Chal. Lett. 6 (12) (2009) 661–671.

21] A. Khare, Effects of Cu concentration on electro-optical and structural proper-ties of chemically deposited nano sized (Zn–Cd)S: Cu films, J. Lumin. 130 (7)(2010) 1268–1274.

22] W. Chen, Z. Wang, Z. Lin, L. Lin, Absorption and luminescence of the surfacestates in ZnS nanoparticles, J. Appl. Phys. 82 (1997) 3111–3115.

23] D. Denzler, M. Olschewski, K. Sattler, Luminescence studies localized gap statesin colloidal ZnS nano crystals, J. Appl. Phys. 84 (5) (1998) 2841–2845.

24] J.P. Borah, J. Barman, K.C. Sharma, Structural and optical properties of ZnSnanoparticles, Chal. Lett. 5 (9) (2008) 201–208.

25] H. Tang, G. Xu, L. Weng, L. Pan, L. Wang, Luminescence and photophysicalproperties of colloidal ZnS nanoparticles, Acta Mater. 52 (6) (2004) 1489–1494.

26] S. Bhushan, S.K. Sharma, Sensitization effect in photoconductivity of CdS, J.Mater. Sci. (Mater. Electron.) 1 (1990) 165–168.

27] S. Bhushan, S.K. Sharma, Sensitization effect in photoconductivity of CdS: Y, J.Phys.: Cond. Matt. 2 (7) (1990) 1827.

28] L. Zhou, Y. Xue, J. Li, Study on ZnS thin films prepared by chemical bath depo-sition, J. Environ. Sci. 21 (2009) S76–S79.

29] P. Nemec, M. Simurda, I. Nemec, P. Formanek, Y. Nemcova, D. Sprinzl, F. Tro-jánek, P. Maly, Chemical bath deposition of CdSe and CdS nanocrystalline films:tailoring of morphology, optical properties and carrier dynamics, Phys. Stat. Sol.205 (2008) 2324.

30] K.U. Isah, N. Hariharan, A. Oberafo, Optimization of process parameters ofchemical bath deposition of Cd1−xZnx films, Leonardo J. Sci. 7 (12) (2008)111–120.

31] S. Bhushan, T. Chandra, Stability effect in photoconducting studies of somechemically deposited films, Turk. J. Phys. 32 (2008) 21–29.

32] H.P. Klug, L.E. Alaxander, X-ray Diffraction Procedures, 2nd ed., Wiley-Intersciences, New York, 1974.

33] A.K. Manna, S.K. Pati, Doping single-walled carbon nanotubes through molec-ular charge-transfer: a theoretical study, Nanoscale 2 (2010) 1190–1195.

34] A.V. Feitosa, M.A.R. Miranda, J.M. Sasaki, M.A. Arujo-Silva, A new route forpreparing CdS thin films by chemical bath deposition using EDTA as ligand,Braz. J. Phys. 34 (2B) (2004) 656–658.

35] U. Ubale, V.S. Sangawar, D.K. Kulkarni, Size dependent optical characteristicsof chemically deposited nanostructured ZnS thin films, Bull. Mater. Sci. 30 (2)(2007) 147–151.

36] J. Manam, V. Chatterjee, S. Das, A. Choubey, S.K. Sharma, Preparation, charac-terization and study of optical properties of ZnS nanophosphor, J. Lumin. 130(2) (2010) 292–297.

37] A.A. Rempel, N.S. Kozhevnikova, A.J.G. Leenaers, S. Van Den Berghe, Towardsparticle size regulation of chemically deposited lead sulfide (PbS), J. Cryst.Growth 280 (1–2) (2005) 300–308.

38] V. Kumar, S.K. Sharma, T.P. Sharma, V. Singh, Band gap measurement in thickfilms from reflectance measurement, Opt. Mater. 12 (1) (1999) 115–119.

39] N. Gaewdang, T. Gaewdang, Investigations on chemically deposited Cd1−xZnxS

thin films with low Zn content, Mater. Lett. 59 (28) (2005) 3577–3584.

40] S. Xu, L. Sun, Y. Zhang, H. Ju, S. Zhao, D. Deng, H. Wang, B. Wang, Effect of fluxeson structure and luminescence properties of Y3Al5O12:Ce3+ phosphors, J. RareEarth 27 (2) (2009) 327–329.

41] G.R. Li, Q. Bu, F.L. Zheng, C.Y. Su, Y.X. Tong, Cryst. Growth Des. 9 (3) (2009) 1538.