4. Luminescent materials and their optical properties

Luminescent materials can be divided into two categories: those that emit a broad band and those that emit fine lines. Depending on the desired effect or application, we'll opt for one or the other. This difference in spectral behavior is due to the nature of the electronic orbitals involved in the optical transitions. The dopant ion interacts with its nearest neighbors in the host lattice and the latter's vibrational modes. This coupling is described in a very simplified way, within the framework of the configuration curve diagram, by the harmonic oscillator model. We consider the coupling between electronic states and network vibrations. For further simplification, we assume that the vibratory mode is totally symmetrical (respiratory mode), so that the energy levels can be represented by parabolas whose minimum corresponds to the equilibrium position of the system in the state under consideration....