Post-Irradiation photoluminescence and thermoluminescence of the ethylene-tetrafluoroethylene copolymer

Abstract

The effect of γ-irradiation on the post-irradiation thermoluminescent and photoluminescent properties of an industrial ethylene-tetrafluoroethylene (ETFE) copolymer was investigated. The radiothermoluminescence (RTL) curve in the temperature range of 77 to 400 K exhibits three maxima: the most intense peak occurs at 116 K, while two additional maxima appear as shoulders at 168 K and 210 K. These maxima result from the formation and subsequent quenching of electronically excited states caused by the recombination of charge carriers accumulated during γ-irradiation of the copolymer at 77 K. Photoluminescence arises from the radiative recombination of excitons formed in the copolymer upon photoexcitation with a xenon lamp at 300 K. The photoluminescence maximum occurs at 340 nm, and its intensity decreases as the γ-irradiation dose increases. Structural defects and macromolecular cross-linking induced by γ-irradiation act as centers of nonradiative exciton recombination, thereby reducing the intensity of the post-irradiation luminescence of the copolymer. Electronic structure predictions of the degradation thermodynamics indicate that polymer backbone degradation through either loss of small unsaturated molecules or carbenes is unfavorable at room temperature but is possible under γ-irradiation conditions.