Unified quantum field theory of light absorption by defect centers

Trapped electrons in crystals are responsible for many important effects on crystals: lattice relaxation, electron-ion correlation, lattice-frequency shift, and so on. These electron-phonon interaction effects cause peak shif ts and give rise to various multiphonon structures in the absorption and em ission spectra of trapped electrons. The present treatment for interactions of trapped electrons with a crystal does not include the standard second-q uantized field theory, which neglects the quantum many-body effects of crys tals. Therefore, up to now no universal light-absorption theory includes va rious effects of trapped electrons on crystals. For this reason, a unified, second-quantized field theory of optical absorption, which contains both l inear and quadratic electron-phonon interactions is established. In this fi eld theory we derive a universal, analytical spectral function of the absor ption coefficient, which describes the whole absorption spectrum of an arbi trary color center. [S0163-1829(99)02547-3].