Energy Transfer in Organic Phosphors

A quantitative theory is developed of the photofluorescence and scintillation properties of organic materials. On this theory the intermolecular energy transfer occurs by photon emission and absorption; the molecular emission spectrum extends continuously from the ionization energy $E_I$ down to the strong fluorescence band normally observed; the emission of primary photons $\sim E_I$ is excited by ionizing radiations; and the subsequent scintillation process consists of a photon cascade, through the emission spectrum. The theory is in agreement with the experimental data on the photofluorescence and scintillations from pure and mixed crystals, and on the scintillations from solutions. It is shown that, because of self-absorption, many of the existing data refer only to the technical fluorescence properties, and a preliminary assessment is made of the molecular properties of the more important organic phosphors.