Emission and Absorption

Abstract

In this chapter we study transitions of the electrons between valence and conduction bands and the associated radiation processes in more detail. Stimulated emission processes turn out to be of special interest. Here radiation induces electron transitions from a high energy level to a lower level, the energy levels being separated by the energy of the emitted photon. The emitted photon is in phase with the exciting radiation and the wave may be amplified as a result. We consider the interchange between light and matter first of all on the basis of generation and recombination processes. This leads to important relationships between absorption and luminescence, as well as conditions for light amplification. A quantum mechanical analysis then allows prediction of the spectral form of the absorption or amplification. As well as bulk matter, quantum structures are also discussed.