INFRARED-ABSORPTION BY 2 LORENTZ OSCILLATORS IN THE SMALL-PARTICLE GEOMETRY - STUDIES ON ANTIRESONANCE

Optical properties of small particles which have two infrared active lattice vibrations are studied. The Maxwell-Garnett theory is used to obtain an analytic solutio for the effective dielectric function of the small particle composite. This solution predicts two resonant absorption peaks whose frequencies are higher than the bulk transverse optic phonon frequencies. When a sharp lattice vibration mode is located in the frequency region of a broad absorption background due to another lattice mode, the absorption coefficient decreases drastically near the sharp mode. This antiresonance phenomenon occurring in the small particle geometry is found to be useful for getting information on optical constants. A possible experimental investigation for the small particle antiresonance is suggested.