Knowledge Bank

“Two types of information about electronic transitions may be obtained from photo-conductivity measurements: $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}$. The close resemblances between the absorption spectrum and the spectral dependence of the photocurrent, including the dependence upon the polarization of the incident light, enable conclusions to be drawn about the polarization of the transitions in the crystal. This will be illustrated for several substances including some for which polarization ratios have not yet been reported from absorption spectroscopy. $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$. Electronic levels in the crystal due to the removal of an electron from one molecule to another or to freedom within or without the crystal must occur to explain intrinsic photo effects such as are observed. The energies and probabilities of transitions to such “ionized” levels in e.g. anthracene and naphthalene have been calculated. The relation of the results to photoconductivity will be discussed.”