The ‘wet dog’ effect in polymers as seen by thermoluminescence

It is shown that maxima of the thermoluminescence (TL) glow curve obtained from irradiated polymer containing molecularly dispersed chromophore coincide with the sub-Tg molecular relaxations, what can be related to the so called ‘wet dog’ effect. Good correlation has been found between the positions of the TL maxima and the molecular β- and γ-relaxations in different poly(alkyl methacrylate)s (alkyl=methyl, ethyl, n-butyl), and polystyrene doped with various chromophores: pyrene, carbazole and perylene. Additionally δ-relaxation has been detected at very low temperatures. The positions of the maxima in the TL spectra are independent of the used chromophore. In spite of the observed coincidence, the activation energies of the detrapping processes determined from the TL experiments are lower than the activation energies of the corresponding molecular relaxations determined from the dielectric spectroscopy. Spectral analyses of the light emitted at temperatures close to the TL maxima show that the ratio between excimeric and monomeric emissions is higher at higher temperatures, reflecting higher ability of the chromophore molecules to form excimers.