Inhomogeneous bleaching of trapped electron absorption bands in aqueous glasses during laser excitation

Abstract

Samples of trapped electrons in aqueous glasses at 77 K were subjected to intense pulses of laser light at 694 nm, which is on the red side of their optical obsorption band maxima. Absorbances were measured at 694, 633, 442 and 1152 nm during and after the excitation pulse so that “transient” and “permanent” bleaching effects could be distinguished. The transient bleaching was very much greater at the photolysing wavelength than at any of the other wavelengths and, furthermore, after the pulse some absorbance returned at 694 nm while it decreased elsewhere across the band. Evidently the band was inhomogeneously bleached and it is, therefore, an inhomogeneously broadened absorption band. An absolute upper limit of 2 × 10–9 s was calculated for the excited state lifetime from the measured transient bleaching efficiency. Several types of process are involved in contributing to the post-pulse development of permanent bleaching, which occur to different extents in aqueous media made with different glass-forming solutes. Results are also presented on the generation of infrared obsorptions, on the effect of added electron scavengers, and on partial bleaching prior to laser excitation.