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

Thermally stimulated luminescence (TSL) glow curves of x-irradiated Estane( R) 5703 exhibit considerable variability as the sample thickness is reduced from 1.25 mm to 20 mu m. 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 rela tively impervious to oxygen exposure, and are characterized by glow peaks a t 145, 405 and 440 K. Radiation-induced optical absorption bands occur at 3 20, 360, 566 and 375 nm, the latter identified with the diphenylmethyl radi cal. Temperature dependence of these bands, coupled with electron-spin-reso nance data, show that TSL is not associated with destruction of the dipheny lmethyl radical, but likely results from the onset of polymer molecular mot ion (gamma relaxation), which releases trapped charges that recombine with other radicals. Radiative emission characteristic of phenyl deexcitation, b ut in the absence of diphenylmethyl radical destruction, implies that recom bination occurs at presently unidentified radical sites, and part of the el ectronic energy is transferred along the polymer chain to the phenyl group. (C) 2000 Elsevier Science Ltd. All rights reserved.