Photoluminescence Quenching and Photo-Induced Charge Transfer Processes in Poly(3-octylthiophene) Polymer Based Hybrid Nano-composites by Ion Irradiation for Possible Optoelectronic Applications

Structural and spectroscopy studies have been carried out on conducting polymer poly(3-octylthiophene) (P3OT) and its copper-doped ZnO (Cu-ZnO/P3OT) hybrid nanocomposites (HNCs) under swift heavy ion (SHI) irradiation at different electronic energy depositions. The photoluminescence (PL) spectra of irradiated films exhibit a significant decrease in the intensity of emissions at higher ion fluences which is ascribed to the trapping of a photo-induced electron-hole by irradiation-induced free radicals and extrinsic non-radiative trap centers leading to the quenching effects. The generation of such free radicals and non-radiative recombination centers occurred through a chemical transformation of polymers in terms of polymer chain disordering, chain scission, chain aggregation, and bond breaking by ion irradiation depending upon the electronic energy depositions and ion fluences. The structural, vibrational, morphological, and optical properties of the irradiated P3OT and Cu-ZnO/P3OT HNCs films have been studied. Interestingly, the glancing-angle x-ray diffraction patterns of irradiated films reveal that the polymer and HNC films retain their chemical structures after high electronic deposition at lower ion fluences which leads to insignificant degradation of polymer and HNCs. However, a relative change in the intensity of characteristic peaks of polymer and ZnO was observed at higher ion fluences and is attributed to the disordering of polymer chains by high electronic depositions. Fourier transform infrared spectroscopy (FTIR) measurements also show similar observation, attributed to a decrease in the intensity of a few methyl and octyl functional groups of P3OT and HNCs. Further, optical study has shown a significant modification in the process of inter-chain and interfacial charge transfer. Finally, from these concurrent effects, PL quenching and photo-induced charge carrier transfer processes are understood by developing a schematic charge transfer diagram.