X-ray-induced thermally stimulated luminescence and electronic processes in a segmented poly(ester urethane)

Abstract

Thermally stimulated luminescence (TSL) glow curves of x-irradiated Estane® 5703 exhibit considerable variability as the sample thickness is reduced from 1.25 mm to 20 μm. The dependence is presumably associated with the diffusion of oxygen into the sample, which alters electronic trapping sites. Specimens of 1.25-mm thickness exhibit reproducible glow curves, are relatively impervious to oxygen exposure, and are characterized by glow peaks at 145, 405 and 440 K. Radiation-induced optical absorption bands occur at 320, 360, 566 and 375 nm, the latter identified with the diphenylmethyl radical. Temperature dependence of these bands, coupled with electron-spin-resonance data, show that TSL is not associated with destruction of the diphenylmethyl radical, but likely results from the onset of polymer molecular motion ( γ relaxation), which releases trapped charges that recombine with other radicals. Radiative emission characteristic of phenyl deexcitation, but in the absence of diphenylmethyl radical destruction, implies that recombination occurs at presently unidentified radical sites, and part of the electronic energy is transferred along the polymer chain to the phenyl group.