Phonon and Spectral Line

The lattice vibration has many effects on spectroscopic properties of active ions in solids, including inducing of electric-dipole transition and vibronic-electronic transition, broadening of spectral line, shifting of spectral line position, introducing of non-radiative transition, and transforming of excited energy between ions. Therefore, studying the interaction of electron with lattice vibration is one of the most important problems in the physics of solid-state laser material. During the discussion of this chapter, the conception of phonon by quantization of lattice vibration will be introduced; the effects of phonon emission and absorption on the spectral line shape, spectral linewidth, and spectral line shifting will be discussed. In these discussions, the concentration of active ions is very low and the interaction between different active ions can be neglected, and the interaction of electronic states of active ions with the electronic band of the crystals is neglected too. The non-radiative transition inside rare earth ions introduced by electron-phonon interaction will be discussed in Chap. 8, while the phonon-assisted energy transfer will be discussed in Chap. 9.