The effects of BaCl2 dopant on the optical properties of poly (vinyl alcohol) have been investigated. Pure and BaCl2 doped PVA films were prepared using solvent casting method. These films were characterized using UV/VIS technique in order to estimate the kind of transition which was found to be indirect transition. The value of the optical energy gap was decrease with increasing dopant concentration.
Refractive index, extinction coefficient and Urbach tail have been also investigated; it was found that all the above parameters affects by doping

Nadir Fadhil Habubi

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Iraqi Journal of Physics, 2012                                                                                             Vol. 10, No.17, PP. 18-22   18 Optical properties of  BaCl2  doped poly (vinyl alcohol) films Nadir Fadhil Habubi1, Bashar Hatem Abed2, Sami Salman Chiad1  1 Physics Department, College of Education, Al_Mustasiriyah University.  2 Chemistry Department, College of Science, Al_Mustasiriyah University. nadirfadhil@yahoo.com, bashar_hatem@yahoo.com, samichiad2003@yahoo.comAbstract Key words    The effects of BaCl2 dopant on the optical properties of poly (vinyl alcohol) have been investigated. Pure and BaCl2 doped PVA films were prepared using solvent casting method. These films were characterized using UV/VIS technique in order to estimate the kind of transition which was found to be indirect transition. The value of the optical energy gap was decrease with increasing dopant concentration.                                                                                        Refractive index, extinction coefficient and Urbach tail have been also investigated; it was found that all the above parameters affects by doping. PVA, Doping,  Optical properties  Article info Received: Oct. 2010 Accepted: May. 2011 Published: May. 2012     دراسة الخصائص البصرية الغشية بولي فينايل الكحول المشوبة بكلوريد الباريومنادر فاضل حبوبي1,بشار حاتم عبد2,سامي سلمان جياد1 1 المستنصرية ة, الجامعةالتربي ة, كليقسم الفيزياء 2 المستنصرية ة, الجامعالعلوم ة, كليقسم الكيمياء  الخالصةاوار ال صارية ولياية باولا ةينايا  الك اوغ ي  غار  اولياية ليار  ااة ة كلوريال ال ااريوم الاو ال تم دراسة تاثير اضااةة اوار  االغ اولياتام ا الميوبة والميوبة بكلوريل ال اريوم ل ولا ةيناي  الك وغ بطريقاة الصا ي ا غ تقنياة لت قا  ماخ  ية ماخ ار واة  قايم ةجاو   مطياف اواعة ةوق ال نفسجية / المرةية وذلك لغار ت ليال عاوال اوعتقااغ والاال  ونال باعال اعتقااغ ليار م اوونال بااة كاةاة  تم الت ق  مخ قيم  معام  اوعكسار , معام  الامود , ذيا  اورباا   الطاقة ال صرية  تق  بازدياد تركيز الياة ةي  الغ المعلما  قل تاثر  بالتيوي ي Introduction        Doping of polymers attracted the scientific and technological researchers, because of their wide applications. The dopant in polymer can changes the molecular structure and hence the microstructure as well as macroscopic properties of the polymer. poly(vinyl alcohol) has been studied extensively due it several interesting properties such as water   soluble, semicrystalline, low electrical, conductivity polymer, relatively low cost in manufacture [1, 2]. Moreover this polymer is considered as an excellent host material for composites. Various research groups studied the effect of doping on optical, thermal, structural, and mechanical properties [3- 12]. These studies shows that the properties like crystallinity, structural order, thermal stability, electrical and optical    Nadir Fadhil Habubi, et  al                            Iraqi Journal of Physics, 2012  19 behavior of the polymer are affected by doping which depends on the interaction between the dopant and the polymer.    This material has potential applications in waveguides [13], nanofibrous composite membrane [14], solid polymer electrolyte [15], fuel cells [16], and integrated       optics [17].    The purpose of the current investigation was to study the effect of BaCl2 doping upon the optical properties of PVA.  Experimental procedure        Poly (vinyl alcohol) with molecular weight 10000 g/mol were used as a host polymeric material in this work. supplied by (BDH chemicals) with high purity,  the aqueous solution of this polymer were prepared by dissolving PVA in a mixed  of deionized water and ethanol and thoroughly stirred  using a magnetic stirrer for about one hour until PVA was completely dissolved.    BaCl2 solution was prepared by dissolving the salt in redistilled water. Appropriate mixtures of PVA and BaCL2 solutions were mixed by a different concentration of salt (2%, 4%, 6%).  The solution was poured into flat glass plate dishes. Homogenous films were obtained after drying in an oven for 24 hours at 40    ْ C. the film thickness was measured with the help of thickness gauge (indicating micrometer) and was found to be in the range of 20 ± 1 m.    Absorptance and transmittance measurements were carried out using double bean UV/VIS spectrometer (shimadzu Japan) in the wavelength range              (190-900) nm.  Results and discussion     The absorptance spectra of pure and Bacl2 doped PVA is shown in Fig. (1), it is clearly seen that the absorptance increase as the doping percentage of BaCl2 increased, the absorption in band at nearly 264 nm was assigned   to -* transition. the absorption edge around 230 nm in pure PVA, it seems that the absorption in band and band edge shift to word higher wavelength as the doping percentage increase these shifts in bands indicate the formation of inter /intra molecular hydrogen bonding mainly between Ba2+ ions with the adjacent OH groups AS the BaCl2 concentration increase inter/intra hydrogen bonding increases and hence absorption [18].             Fig. (1) Absorptance versus wavelength for the as deposited films.     The optical absorption coefficient of PVA and BaCl2 doped PVA is very important because it provides information on the electronic transition by using the following equation [19]: hEhBg2)(                       (1) where  is the absorption coefficient,  a constant, h is the photon energy, Eg is the energy gap.   Figures (2), (3), (4) show the relationship between (h)1/2 and photon energy , as can be seen from the figures that the value of the energy gap was decrease as the doping percentage increased show an indirect allowed transition, these values were (5, 4.7, 4.6, 4.5) eV respectively. The existence and variation of optical energy gap may be Iraqi Journal of Physics, 2012                                                                                             Vol. 10, No.17, PP. 18-22   20 explained by invoking the occurrence of local cross linking within the amorphous phase of the polymer, in such a way as to increase the degree of ordering in these parts as a result of Ba2+ ion of BaCl2 which interact with-OH group of PVA.               Fig. (2) (αhν)1/2 versus photon energy for pure PVA  films.              Fig. (3) (αhν)1/2  versus photon energy for BaCl2  doped PVA  films.     It is known that the absorption coefficient near the band edge shows an exponential dependence on photon energy [20]:  )Eh(expUo                               (2)   Where () is constant, (h) is the photon energy, and EU is the Urbach energy which corresponds to the width of the band tail and can be evaluated as the width of the localized state. Fig.(6) shows the dependence of ln () on photon energy Urbach energy were calculated from the reciprocal gradient of these linear portion and found to be increase as the doping percentage increased, their values was (477, 510, 539, 567) meV respectively. The EU value change inversely with the optical band gap, the decrease in Eg is attributed to the increase of disorder of the polymer occurred by doping.             Fig. (4) (αhν)1/2  versus photon energy for BaCl2  doped PVA  films.                   Fig. (5) (αhν)1/2  versus photon energy     for BaCl2  doped PVA  films.  The refractive index (n) was determined from the reflectance (R) data using the relation [21]:    Nadir Fadhil Habubi, et  al                            Iraqi Journal of Physics, 2012  21 22)1(4)1()1(kRRRRn          (3) where k is the extinction coefficient and absorption coefficient can be related by [21]:            Fig. (6)  ln   as a function of h.     4k                                         (4)    As shown from Fig. (7), the refractive index decreases as the wavelength increase until 400 nm and then become nearly constant with increasing wavelength, the value of refractive index within the constant range was varying from 1.5-1.65 as the doping percentage increase. These values are in good agreement with the values obtained by other workers concerning PVA films [22,23].                Fig. (7) Refractive index versus wavelength for the as deposited films.  Fig. (8) shows the dependence of the extinction coefficient on wavelength, it can bee seen that extinction coefficient decrease until in 260 nm and then became to increase showing a noticble peak around 285 nm and then decrease again until 360 nm then became nearly constant, we can deuce from the graph that k increase as the doping percentage increased.              Fig. (8) Extinction coefficient versus wavelength for the as deposited films. Conclusions    PVA and BaCl2 doped were prepared by casting technique. The constant transparency in the visible and near IR region revealed that this polymer can be used as an optical window within this spectral region. The optical energy gap Urbach tail assures that the crosslink is increased as the doping percentage increase. The optical energy gap was found to be indirect, and all the value of the optical parameters under consideration was increased by doping.  References  [1] A. Tawansi, M. D. Migahed and M. I. A. 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Optical properties of BaCl2 doped poly (vinyl alcohol) films

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Optical properties of BaCl2 doped poly (vinyl alcohol) films

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