Abstract
In recent years the rapid advances in the understanding of the nature of chemical bonds and in the application of quantum mechanics to chemical problems have imparted a great impetus to studies of luminescent materials, studies which have been primarily directed toward the elucidation of the electronic structures of the molecules. Great strides have been made in the understanding of organic materials employing the complementary studies of absorption, fluorescence, and phosphorescence, the latter a comparatively recent development.1