Unraveling the luminescence signatures of chemical defects in polyethylene

TL;DR

This study combines advanced computational methods to accurately identify and assign luminescence peaks to specific chemical defects in polyethylene, improving understanding of defect-related electrical property degradation.

Contribution

It introduces a comprehensive computational approach beyond traditional methods to determine defect levels and assign luminescence signatures in polyethylene.

Findings

Calculated defect transition levels match observed luminescence spectra

Clarified the origins of specific luminescence peaks in PE

Proposed a computationally efficient method for defect analysis in polymers

Abstract

Chemical defects in polyethylene (PE) can deleteriously downgrade its electrical properties and performance. Although these defects usually leave spectroscopic signatures in terms of characteristic luminescence peaks, it is nontrivial to make unambiguous assignments of the peaks to specific defect types. In this work, we go beyond traditional density functional theory calculations to determine defect-derived emission and absorption energies in PE. In particular, we characterize PE defect levels in terms of thermodynamic and adiabatic charge transition levels that involve total energy calculations of neutral and charged defects. Calculations are performed at several levels of theory including those involving (semi)local and hybrid electron exchange-correlation functionals, and many-body perturbation theory. With these critical elements, the calculated defect transition levels are in excellent correspondence to observed luminescence spectra of PE, thus clarifying and confirming the origins of the observed peaks. Based on this work, a prescription with a reasonable computational expense is proposed to accurately predict and assign spectroscopic signatures of defects in other organic polymers as well.