Urbach Rule in the Red-Shifted Absorption Edge of PET Films Irradiated with Swift Heavy Ions
Tuleushev A.Z. Harrison F.E. Kozlovskiy A.L. Zdorovets M.V.
March-1 2022MDPI
Polymers
2022#14Issue 5
This paper presents a new analysis of the experimental transmission spectra of polyethylene terephthalate (PET) films before and after irradiation with swift heavy ions (SHI) films, as reported previously by the authors. It is shown that the absorption edge red shift for irradiated films contains two regions of exponential form, one of which is located in the UV region and the other at lower energy, mainly in the visible part of the spectrum. The behaviour of the transmission curves under different irradiating fluences demonstrates that these two regions reflect respectively the electron-enriched core of the latent track and its electron-depleted peripheral halo. The focal point method yields a bandgap energy of 4.1 eV for the electron-enriched core of the latent track, which is similar to n-doped semiconductors, and a bandgap of about 1.3–1.5 eV for the electron-depleted halo, similar to p-doped semiconductors. The boundary between the latent track cores and halos corresponds to a conventional semiconductor p-n junction. The values of the characteristic Urbach energy determined from experimental data correspond to the nonradiative transition energy between the excited singlet and triplet levels of benzene-carboxyl complexes in repeat units of the PET chain molecule. A parallel is drawn between the SHI-induced redistribution of electrons held in structural traps in the PET film and chemical redox reactions, which involve the redistribution of electrons in chemical bonds. It is suggested that alkali etching triggers the release of excess electrons in the latent track cores, which act as a catalyst for the fragmentation of PET chain molecules along the latent tracks of the SHI irradiation.
Bandgap energy , Latent track , Polyethylene terephthalate , SHI irradiation , Urbach energy
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Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna, 141980, Russian Federation
Engineering Profile Laboratory, L.N. Gumilyov Eurasian National University, Nur-Sultan, 010008, Kazakhstan
Laboratory of Solid-State Physics, The Institute of Nuclear Physics, Almaty, 050032, Kazakhstan
Department of Intelligent Information Technologies, Ural Federal University, Yekaterinburg, 620075, Russian Federation
Flerov Laboratory of Nuclear Reactions
Engineering Profile Laboratory
Laboratory of Solid-State Physics
Department of Intelligent Information Technologies
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