ABSTRACT
This chapter defines the luminescence of organic compounds. It should be emphasized that any kind of luminescence in organic compounds is due to well-defined electronically neutral singlet or triplet excited states in the organic molecules, even though luminescence can be produced by a variety of excitation methods photoluminescence, chemiluminescence, electrochemiluminescence, triboluminescence, thermoluminescence, and electroluminescence. Aromatic hydrocarbons such as anthracene and perylene, for example, show a characteristic broad, featureless excimer fluorescence. Anthracene crystals doped with a trace amount of tetracene, for example, never give characteristic anthracene emission, but yield the tetracene emission spectrum instead, although the absorption spectrum still looks the same as that of anthracene. Therefore, the effects of trace amounts of impurities incorporated in organic solids should be carefully considered. Aromatic hydrocarbons form important groups among fluorescent compounds, which emit light in the violet to blue regions, and their quantum yields are fairly high even in crystalline states as well as in solutions.
