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Effect of Gamma Radiation on Optical Energy
Gap of Crystal Violet Doped Polystyrene Films
1
Mahasin F. Hadi Al-Kadhemy, 2Sanaa R. Salim , 3 Haider S. Hussain, 4Wafaa 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 (390 – 900) 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 Io
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
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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 0.5×10-4 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, El04113001) in the wavelength range
(300- 900) 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
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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 (Eg) 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)
a-
Figure 4 Energy gap for 5 ml CV - PS film
Non –radiated b- radiated with 200 rad. Gamma radiation
(a)
a-
(b)
(b)
Figure 5 Energy gap for 10 ml CV - PS film
Non –radiated b- radiated with 200 rad. Gamma radiation
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a-
a-
Figure 6 Energy gap for 15 ml CV - PS film
Non –radiated b- radiated with 200 rad. Gamma radiation
a-
Figure 7 Energy gap for 25 ml CV – PS film
Non –radiated b- radiated with 200 rad. Gamma radiation
Figure 8 Energy gap for 35 ml CV - PS film
Non –radiated b- radiated with 200 rad. Gamma radiation
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(a)
(b)
a-
Figure 9 Energy gap for 40 ml CV – PS film
Non –radiated b- radiated with 200 rad. Gamma radiation
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; Eg= 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.
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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)
2.8
1.8
1.88
1.8
1.78
1.81
1.9
2.8
1.79
1.79
1.76
1.74
1.85
1.68
Energy gap of CV-PS radiated
with 200 rad. of Gamma radiation
(eV)
4. 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.
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