Anomalous thermal behaviour of induced phosphorescence in irradiated, doped polymeric glasses

Abstract

WE report here that the intensity of induced phosphorescence in pre-irradiated, doped polymethylmethacrylate (PMMA) glasses changes in an anomalous way with temperature. At room temperature the irradiated part of the sample shows intense phosphorescence after ultraviolet excitation with an inspection lamp1, whereas the part of the sample not previously irradiated shows no afterglow. When, however, the sample is cooled to the temperature of liquid nitrogen and the ultraviolet photoexcitation is repeated, the irradiated spot appears dark on the bright afterglow background of the rest of the sample (Fig. la and b). In Fig. 1a the central, ultraviolet irradiated, spot is seen as a bright circular region at room temperature after excitation with an ultraviolet inspection lamp; Fig. 1b shows the same irradiated spot, now relatively dark, after the sample has been cooled to 77 K and excited by the same inspection lamp.