Kinetic investigations of the radiophotoluminescence of frozen organic compounds. Tunneling mechanism of light emission

Abstract

The main kinetic patterns of the radiophotoluminescence (RPL) of organic substances at 77 K have been studied. It was established that the kinetics of the long-lived RPL component is determined by the sum of two processes: monomolecular, corresponding to the spontaneous deactivation of the charges of the triplet molecules formed on recombination of charges, and quasi-monomolecular the kinetics of which is determined by the recombination of electroncation pairs. For a number of aliphatic substances at radiation doses of more than 1 Mrad it was possible to find quenching of RPL manifest in an appreciable change in the luminescent characteristics. From the experimental findings it may be concluded that the quenching observed is due to the free radicals formed in the course of radiolysis and which are effective electron acceptors. A theoretical model of RPL is proposed based on the concepts of the tunnelling mechanism of charge migration in the irradiated frozen organic substances. In examining the processes of paired recombination of spatially separated charges consideration was given to the role of the processes competing with them for capture of one of the components of the pair (electron) by free radicals. The model satisfactorily explains the experimentally observed hyperbolic character of the decay of the long-lived RPL component, the shortening of the duration of luminescence with a rise in the radiation dose and an absence of the effect of temperature on the kinetics of RPL.