Characterizing the Dosimetric Properties of MEH-PPV Using Thermoluminescence (TL)
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Characterizing the Dosimetric Properties of MEH-PPV Using Thermoluminescence (TL) Alejandro Ortiz-Morales1,3, Ramón Gómez-Aguilar1, Jaime Ortiz-Lopez2, Epifanio Cruz-Zaragoza3 1
Unidad Profesional Interdisciplinaria de Ingeniería y Tecnologías Avanzadas, IPN, Av. Instituto Politécnico Nacional 2580, Col. La Laguna Ticomán, 07340 México DF., México 2 Escuela Superior de Física y Matemáticas, IPN, Av. Instituto Politécnico Nacional s/n, Col. San Pedro Zacatenco, 07738 México DF., México 3 Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, AP. 70543, 04510 México DF., México ABSTRACT The thermoluminiscent properties of MEH-PPV and MDMO-PPV conjugated polymers were studied in order to verify if they are suitable for use as TL dosimeter. The dose response that was analyzed cover the wide dose range 0.34-5.44 kGy. The measured glow curves show complex structures which were evaluated with kinetic parameters based on the MO (Mix Order) model together with the CGCD (Computerized Glow Curve Deconvolution) homemade program which is useful to understand the mechanisms responsible for TL emission. INTRODUCTION The polymer poly(p-phenylene vinylene), abbreviated as PPV, consists of a chain of phenylene rings intercalated by vinylene bridges. MEH-PPV and MDMO-PPV are modified forms of the parent PPV polymer with additional methyl-based side groups attached to the polymer backbone. These polymers show optical absorption and photoand electro-luminescence bands in the visible region which make them important candidates for many electronic applications. In the past twenty years, flexible electrooptical devices such as organic light emitting diodes (OLEDs), organic field effect transistors (OFETs) and organic photovoltaic cells (OPVCs) have been developed with the use of thin films of semiconducting conjugated polymers like MEH-PPV and MDMO-PPV [1-3]. Thermoluminescence(TL) technique has been widely used to know if some crystalline solids doped with different metallic ions[4][5] and rare earths[6] are candidates for Thermoluminiscent Dosimeters (TLD), such as: LiF:Mg:Ti(TLD-100)[7], CaSO4:Dy(TLD-700)[8]. Recent studies of MEH-PPV have showed that this polymer could be used as a radiation sensor [9]. For this reason, interest has grown for the analysis of MEH-PPV and MDMO-PPV with TL. The aim of this work, is to report if the MEH-PPV and MDMO-PPV polymers have suitable TL properties for their use in dosimetry.
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EXPERIMENTAL DETAILS Samples A and B used in this work were MEH-PPV and MDMO-PPV, respectively, obtained commercially from Sigma Aldrich. Details of the samples are given in Table 1, and the values of the atomic weight (Wt). Table 1. Conditions of sample preparation. Preparation
Sample
Mass [mg]
Molecular Weight (Mw) [mol]
A B
MEH-PPV MDMO-PPV
4 4
150,000-250,000 23,000
Samples (A, B) were deposited on aluminum disk in proper amounts and were exposed to gamma photons from 60Co of irradiator GammaBeam 650PT of the ICNUNAM with dose rate of 0.170 kGy/min. After irradiating at room temperature (
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