Solids are made up of atoms bound together in crystals, and the understanding of their quantized states is a subject in its own right, namely solid-state physics. In this chapter, we briefly look to see how the general principles developed in atomic physics can be applied to solid-state systems. This will enable us to obtain a basic understanding of light emission in solids. The focus of the chapter will be restricted to two main examples of optically active solid-state materials:
In both cases, it will not be possible to give a comprehensive treatment; the aim of the chapter is to explain a few basic principles that can lay the foundations for further study. This author has written another book in which these topics are explained in much greater depth. See Fox (2010).
Chapter 3 developed the basic principles governing optical transitions in atoms. In this section, we shall see how these principles carry over to solid-state systems.
The electric-dipole (E1) interaction is the strongest term in the light-matter Hamiltonian, as discussed in Section 3.3. The selection rules that follow from analysis of the E1 perturbation and the wave functions of atomic states were derived in Section 3.4, and are summarized in Table 3.1. These selection rules carry over directly to optical transitions in solid-state systems.