A study was made of the temperature-dependent absorption spectra of FH (CN-) defect pairs. Two distinct absorption peaks were observed at the lowest temperature. As the temperature was increased, the separation of the peaks decreased, the relative oscillator strengths changed, and the peaks broadened. These results were explained in terms of a simple model which assumed that the nearly degenerate 2s and 2pz electronic states of the F center were strongly mixed by the intrinsic and displacement dipole moments of the CN- molecule. Important parameters were deduced from the results, such as the coupling constants, the effective phonon-mode frequencies which participated in the absorption process, and a parameter which described the degree of 2s-2pz mixing. These were essential data for testing physical models which had been proposed for electronic to vibrational energy transfer in this defect system.

J.West, K.T.Tsen, S.H.Lin: Physical Review B, 1994, 50[14], 9759-66