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  • Print publication year: 2018
  • Online publication date: June 2018

11 - Atomic Physics Applied to the Solid State

from Part II - Applications of Atomic Physics


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:

  • (i) Semiconductors: Semiconductors lie at the heart of modern technology. The silicon chip underpins the electronics industry, while the optoelectronics industry exploits the optical properties of compound semiconductors such as GaAs. Our task here will be to apply simple principles of atomic physics to understand the electronic states of impurities in semiconductors, and the mechanisms of light emission and detection.
  • (ii) Ions doped into optical hosts: Here we consider materials such as ruby, where chromium is lightly doped into Al2O3, with the Cr3+ ions substituting for the Al3+ ions in the crystal. Pure Al2O3 is a colorless, transparent crystal, and the characteristic red color of ruby arises from transitions associated with the Cr3+ ions. Our task will be to understand how the transitions of the Cr3+ ions in the crystal relate to the atomic states of Cr3+ ions in isolation.
  • 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).

    Solid-State Spectroscopy

    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.

    Selection Rules

    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.

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