Luminescence Phenomena in Gamma-Irradiated Pure Alkane Glasses: Relaxation Mechanisms

It has been shown previously that gamma-irradiated pure 3-methylpentane glass at 77°K emits a characteristic luminescence according to a law which can be expressed as the sum of three first-order decays. In this new work on both 2-methylpentane and 3-methylpentane, it is shown: (1) that the two pentanes emit at 77°K, as nearly as can be established, in precisely the same fashion; (2) that the intensity of luminescence is decreased and the decay curve is flattened by permitting the glassy sample to relax at 77°K between vitrification and gamma irradiation; (3) that the decay law at both 77°K and 90°K is the sum of three first-order decay laws; (4) that the activation energies, as established by fixed-temperature measurements at those two temperatures, are all near 0.04 (±0.01) eV, but that the characteristic frequencies of the three laws vary by a factor of ∼102; (5) that, in addition to light which appears isothermally at 77°K and which is stimulated also by infrared irradiation, there is a glow portion which begins to appear only at temperatures near 100°K; (6) that while the long-wavelength portion of the luminescence spectrum is unaffected by the treatment to which the sample is subjected, there are significant changes in the shorter wavelength region on prolonged irradiation; (7) that at least two different kinds of electron traps are involved; (8) that chemical products are involved in the luminescence; and (9) that in gamma-sensitized luminescence as well as in radiation chemistry, radiolytic products play an important role in determination of the elementary processes responsible for the effects observed.