Antiresonance in the Optical Absorption Spectra of the Impurity in Solids

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Abstract
The optical absorption spectra of an impurity atom or molecule in the crystal is investigated by applying Fano formula to a simple model in which a discrete spectrum due to the excitation within the impurity atom or molecule overlaps with the continuum due to transition between the impurity ground state and the energy band of the host crystal. The change of the line shape caused by the interference between them is studied for various values of the parameters associated with the transfer energy and the dipole matrix element in order to clarify the condition for the antiresonance to occur. A favorable situation is that the intra-atomic transition of the impurity is forbidden or sufficiently weak but the excited state couples appreciably with that part of the continuum to which the transition is allowed.