Absorption and emission of light by systems with closely spaced energy levels

Abstract

A complete solution of the time-dependent Schrodinger equation for the overall absorption-emission process is presented for a particular model system possessing an excited state manifold of (nearly) uniformly spaced molecular eigenstates with a lorentzian distribution of transition moment. Results for both narrow and broad band excitation are derived, and it is shown that the fluorescence quantum yield is essentially the same for both broad band and narrow band excitations. It is argued that the lifetime of the incident photon state is important in determining the presence or absence of structure in the absorption spectrum and, consequently, that the absorption spectrum observed depends upon both the optical density of the sample and the intensity of the incident light.