Gamma-Ray Induced Luminescence of Silica Gel II. Luminescence Occurring on Adsorption of Gases: Radiosorptionluminescence

Luminescence observed on adsorption of gases and vapours (RSL) on silica gel previously exposed to y-rays has been investigated. The dependence of RSL intensity on absorbed radiation dose and degassing temperature of the gel prior to irradiation parallels the dependence of radiothermoluminescence (RTL) intensity: A limiting value is reached around 1 Mrad and the intensity increases steeply on raising the degassing temperature. The RSL intensity is largest on adsorption of H2 and decreases in the order H2 ; 0 2 ; N 2 0 ; N2 ; He. The stronger the RSL effect, the more is the subsequent measured RTL reduced. The RSL emission spectrum has a maximum at 450 nm and is identical with the spectrum of RTL. In some cases bands at longer wavelengths have been observed. The RSL decays with hyperbolic kinetics which may be related to the logarithmic rate of adsorption as given by the Elovich equation. The results are discussed in terms of detrapping of charges, in this case stimulated by adsorption, and the recombination of carriers leading to excitation of luminescent centers as in RTL. The emission bands at longer wavelengths are thought to involve electron transfer from interacting molecules neutralizing holes trapped in the solid.