Wavelength-selective bleaching (``burning holes'') in the optical spectra of trapped electrons in organic glasses

This paper presents experimental evidence confirming that the broad optical absorption spectra of trapped electrons in glassy 3-methylpentane and methyltetrahydrofuran (MTHF) are convolutions of spectra of electrons trapped with different energies. Laser light of wavelengths near or to the red of the et− optical absorption maximum selectively depopulates electrons which absorb at the bleaching wavelength, thus creating a hole in the et− spectrum. Some additional indications as to the spectral properties of the individual electrons are given by the observations that (1) illumination of et− produced in MTHF at 25°K with laser light to the blue of the absorption maximum results in nearly uniform bleaching throughout the spectrum; (2) et− produced in MTHF at 67°K and illuminated at 25°K with 1064 nm are bleached less efficiently then et− produced at 25°K and have a low probability of being shifted to traps typical of mobile electron trapping at 25°K; (3) the spectra of et− in MTHF are progressively red-shifted as the temperature at which they are produced is lowered from 97 to 10°K, and the resolution of the peaks observable in the spectrum produced at 72°K is lower for spectra of et− produced at higher (97°K) or lower (25 and 10°K) temperatures. Some implications of these observations are discussed.