Effect of Gamma Radiation on Optical Energy Gap of Crystal Violet Doped Polystyrene Films

Transcription

1 Effect of Gamma Radiation on Optical Energy Gap of Crystal Violet Doped Polystyrene Films 1 Mahasin F. Hadi Al-Kadhemy, 2 Sanaa R. Salim, 3 Haider S. Hussain, 4 Wafaa A. Hameed 1,2,4 Al-Mustansiriya Univ.- College of Science- Physics Dept. 3 Baghdad Univ.- College of Science- Physics Dept. Baghdad / IRAQ ABSTRACT Optical energy gap was investigated for crystal violet doped polystyrene in different doping ratio of crystal violet solution ( 5, 10, 15, 25, and 40 ) ml from their optical absorption spectra in ( ) nm for both irradiated and un irradiated with Gamma radiation. The dose of Gamma radiation was 200 rad.. The optical energy gap for pure PS lay at 2.8 ev while it ranged from 1.68 to 1.9 ev for differently doped samples. It was found that the energy gap values shifted to low energies when irradiated with Gamma radiation. Key words:- Band Gap Energy, Gamma Radiation, Crystal Violet, Polystyrene, Dye Doped Polymer. 1. INTRODUCTION The optical properties of dye doped polymer films have attracted much attention in recent years, because of their large applications in optical devices with remarkable reflection, antireflection, interference and polarization properties as demonstrated by [1]-[4]. Exposure material with any form of electromagnetic radiation or high energy electrons is known as irradiation. Electromagnetic radiation is essential for modern life. It includes X rays, ultraviolet UV, visible light, infrared IR, and microwave radiation as explained by [5]. Optical absorption studied are provide information of electronic band structures, localized states and type of optical transitions, making these materials very attractive for chemical sensors and for display panels, reported by [6]-[8]. The absorbance is defined by, mentioned by [9] : (1) Where I o doped polymer films was taken from absorption spectrum using the following equation, demonstrated by [9],[10] : (2) where d is the thickness of the sample. The absorption edge coefficien [5],[11] : (3) where h is p g the optical energy band gap, B constant known as the disorder parameter independent of photon energy, r is power coefficient, the value of it is determined by the type of electronic transition ; r = 1\2,3\2,2, or 1\3 for direct allowed, direct forbidden, indirect allowed and indirect forbidden, respectively, [12], [13]. In this work, we aim to synthesis the optical energy band gap of PS- CV films, prepared by casting method before and after irradiated by Gamma radiation and show the effect of change the doping ratio of CV solution on it. 2. Experimental Work Crystal violet (CV) or called methyl violet (2B), has chemical formula C24H27N3HCl with molecular weight Mw=393.95gm/mol, [14]. We choose polystyrene polymer as host material for laser dye due to its excellent optical properties. The molecular formula of PS is-[-ch(c6h5)-ch2]-n, highly amorphous, melting temperature 270oC, and Volume 2, Issue 5, May 2013 Page 511

2 glass transition temperature 100oC[15]. It is an aromatic polymer made from the aromatic monomer styrene, a liquid hydrocarbon that is commercially manufactured from petroleum by the chemical industry. Polystyrene is a thermoplastic substance and one of the most widely used kinds of plastic. Casting method is used to prepare dye doped polymer films. Certain amounts of polymer PS granules(1gm)were dissolved in (10 ml) of solvent chloroform, that is suitable solvent for both dye and polymer. The dye solution with concentration mol/liter is prepared according to the method mentioned in ref. [16]. Then, different ratio of dye solution (5, 10, 15, 25, 35, and 40)ml were added to polymer solution and mixed very well. The mixture poured in glass petri dish with (10cm) diameter and left to dry for 24hr at room temperature about(25 C) to get homogeneous films. Crystal Violet doped PS films were irradiated to Gamma radiation using 60CO radiation facility at a constant dose rate at room temperature. The dose was taken 200 rad. The absorption spectra were measured by UV-Visible spectrophotometer type(cary 100 Conc., UV-Visible, Spectrophotometer Varian, El ) in the wavelength range ( ) nm. 3. Results and Discussions The UV-Visible absorption spectra of the CV-PS films were measured at different doping ratio of CV solution as shown in fig.(1). Figure 1 Absorption spectrum of Crystal Violet doped polystyrene films in different doping ratio of CV solution After irradiated all films with Gamma radiation with dose 200rad, the absorption spectra of these CV-PS films were illustrated in fig.(2). Figure 2 Absorption spectrum of Crystal Violet doped polystyrene films in different doping ratio of CV solution after irradiation by Gamma radiation Volume 2, Issue 5, May 2013 Page 512

3 The band gap energy represents the minimum energy difference between the top of the valence band and the bottom of conduction band. The energy gap for pure PS film is shown in fig. (3), and its value (2.8) that which is matched with the result obtained by [17]. Also, we compute this energy for all films before and after irradiated with 200 rad of Gamma radiation as shown in figs.(4-9), respectively. The determination of band gap energy (E g ) is often necessary to develop the electronic band structure of film material. The optical band gap is the value of optical energy 1/r b Figure 3 Energy gap for pure PS film (a) Figure 4 Energy gap for 5 ml CV - PS film (b) (a) (b) Figure 5 Energy gap for 10 ml CV - PS film Volume 2, Issue 5, May 2013 Page 513

4 Figure 6 Energy gap for 15 ml CV - PS film Figure 7 Energy gap for 25 ml CV PS film Figure 8 Energy gap for 35 ml CV - PS film Volume 2, Issue 5, May 2013 Page 514

5 (a) (b) Figure 9 Energy gap for 40 ml CV PS film The energy band gap for (CV) solution was (2.01) ev calculated from fig. (10). This value is agreement with the value obtained by Zahraa and Ismail [19]. Figure 10 Energy gap of CV with concentration 0.5x10-4 mol/liter Table (1) was given all values of energy gap; where the highest values at CV= 40ml; E g = 1.9eV, and decreased after irradiation to 1.68eV. whereas, the energy band gap for 35ml become greater after irradiation because the transitions for absorption spectrum that refer to peaks become more clear. From these results, we can deduce that energy gap represents the gap for dye entered as impurities that lead reducing the amount of energy gap. Volume 2, Issue 5, May 2013 Page 515

6 Table 1: Energy gap of CV-PS films for different doping ratio of CV solution before and after radiated by 200 rad. Gamma radiation Doping ratio of (CV) Pure PS 5ml 10ml 15ml 25ml 35ml 40ml Energy gap of CV- PS (ev) Energy gap of CV-PS radiated with 200 rad. of Gamma radiation (ev) Conclusions The energy gap for Polystyrene film was calculated from UV-Visible absorption. Energy gap for dye crystal violet doped polystyrene films decreased. The addition of crystal violet to polystyrene films produced instability against radiation, it is sensitive to dyes. References [1.] M. A. El- Shahawy and A. F. Mansour, Optical Properties of Some Luminescent Solar Concentrator, J. Mater. Sci. Mater. In elect., 7, pp. 171, [2.] N.A.Baker, A. F. Mansour and M.Hammam, Optical And Thermal Spectroscopic Studies of Luminescent Dye Doped Poly(Methyl Methacrylate) as Solar Concentrator, J. Appl. Polym. Sci., 74, pp. 3316, [3.] A. F. Mansour, M. G. El Shaarawy, S. M. El Bashir, M. K. El Mansy and M. Hammam, Optical Study of Perylene Dye Doped PMMA Used as Fluorescent Solar Collector, Polymer Int. 51, pp , [4.] H.M.Zidon, A. Tawansi, and M. Abu Elnader, Miscibility, Optical and Dielectric Properties, of UV Irradiated Poly(Vinylacelate ) \ Poly Methylmethacrylate, Physica B, 339, pp , [5.] B.A. Hasan, M. A.Saeed, and A. A.Hasan, Optical Properties of Poly Vinyl Chloride PVC Films Irradiated with Beta And Gamma - Rays, British. of Sci., 7 ( 1 ), pp , [6.] A. Arshak, and O. Korostynska,, Gamma Radiation Dosimetry using Tellurium Dioxide Thin Film Structures,Sensors, 2, pp , [7.] K. AL Ani, I. H. Al Hassany and Z. Al Dahan, The Optical Properties and A.C. Conductivity of Magnesium Phosphate Glasses, J. Mater.Sci., 30, pp , [8.] N.F.Habubi, H. G.Rashid, S. M. Ahmad, Effect of Thickness Variation on The Optical Properties of CUO Thin Films, Atti Della " Fondazione Giorgio Ronchi", 5, pp , [9.] J.Touc, Optical Properties of Amorphous Semiconductor, plenum press, London, pp. 159, [10.] N.F Mott, and E. A. Davis, Electronic Processes in Non Crystalline Materials, Claredon press,oxpord, ( 1979 ). [11.] J.L.Pankov, optical process in Semiconductors, London, [12.] L. K. Chopra, and I. Kaur, " Thin film Devices Applications " Plenum Press, New York, [13.] M.Ohring, Materials science of thin films 2nded, Academic press, [14.] The free encyclopedia crystal violet. [15.] K. Myer, (Handbook of Materials science ), John Wiley& sons, (2002). [16.] M.F. Hadi Al Kadhemy, and W. H.Abaas, Absorption spectrum of crystal violet in chloroform solution and doped PMMA thin films, Atti Della " Fondazione Giorgio Ronchi", 3, pp , [17.] M. R. Fraih Study of Thermal Aging Effect on Optical Properties of Some Polymer Blends MSC thesis University of Technology Department of Applied Sciences, [18.] Raja, A.K. Sarma, V.V. Narasimharao Optical properties of pure and doped PMMA-CO- P4VPNO polymer films, Materials letters, 37, pp , [19.] Zahraa Z. Yousif, and Ismail K. Abbas, The Effect of the Acid HCl Concentration on the Optical Properties of P-Crystal Violet, Rafidain journal of science, 21 ( 1A), pp , Volume 2, Issue 5, May 2013 Page 516