Knowledge Bank

Trapped electrons produced in ethanol glass by $\gamma$-irradiation have two distinct peaks, one in the visible (deep trap) and the other in the infrared (shallow trap). These two peaks are apparently attributable to electrons in two different sites of the solid matrix, a phenomenon known in solid-state spectroscopy as the Shpolskii effect. The nature of the sites and the excited states is not well-understood. Theoretically, the situation is similar to the discrete-state-embedded-in-a-continum language used in the theory of radiationless transitions. Three continua, however, are involved: namely, the conduction band continuum and the radiative and non-radiative continua. The coupling between the discrete states and the conduction band leads to photoconductivity and trap-to-trap migration. The couplings between the discrete state and the radiative and non-radiative continua lead to luminescence and radiationless transitions, respectively. An attempt has been made to understand the lifetime and the different modes of decay of the excited state, and hence the line shape function of the trapped electron absorption. Photobleaching, using an approximately 10 nanosecond pulse of 3372 \AA emission from a megawatt nitrogen laser, and simultaneous monitoring of the absorption peaks in the visible and in indicate that the uv tail-end of the deep trap absorption is predominantly dissociative. A fast ( sec) disappearance of the visible band and concurrent appearance of the ir band were observed. A further experiment with dye laser emission in the visible region is being carried out to see if molecular-type radiationless transitions are a predominant mode of decay in the lower frequency region of the absorption (and thus possibly indication a bond state).