Specialty Optical Fibers Handbook

The absorption of UV or visible radiation corresponds to the excitation of

outer electrons. The absorption in organic molecules is restricted to certain

functional groups (chromophores) that contain valence electrons of low excita-

tion energy. The spectrum of a molecule containing these chromophores is

complex. This is because the superposition of rotational and vibrational transi-

tions on the electronic transitions gives a combination of overlapping lines. This

appears as a continuous absorption band. Many inorganic species (such as

semiconductors) show charge–transfer absorption and are called charge–transfer

complexes. For a complex to demonstrate charge–transfer behavior, one of its

components must have electron-donating properties and another ...