The decay of excited states

Abstract

This chapter investigates two modes of radiative decay in which radiation is emitted spontaneously by molecules in excited states: fluorescence and phosphorescence. It discusses the reduction in efficiency of emission through quenching, which is interpreted in terms of the rates of physical and chemical processes that compete for the energy stored in excited states of molecules. It also highlights the detection of photons that are emitted when excited electronic states decay radiatively back to the ground state. The chapter looks at how molecules in excited electronic states discard their excess energy by emission of electromagnetic radiation, transfer as heat to the surroundings, fragmentation, or reaction. It describes the excitation energy of a molecule that has absorbed a photon and is degraded into the disordered thermal motion of its surroundings by non-radiative decay.