Organic compounds have been the subject of intense theoretical and experimental studies due to their promising applications in different life science fields. The organic compounds that emit at different wavelength regions have been selected to study. The principles concerning the electromagnetic radiation interaction with organic matter atoms and molecules, and gamma ray interaction are covered at the beginning of this chapter. The main source of information about this interaction can be covered via study the photo-physical processes for these materials. In these processes, the radiative and nonradiative transitions represent the main route of energy relaxation of an excited state of organic molecule, dyes classification, intermolecular competing processes, gamma ray, and interaction of gamma ray, action of irradiation and interaction processes.