Abstract
Abstract High resolution FTIR absorption spectroscopy in the 600–3500 cm−1 wavenumber and 9–300 K temperature ranges was applied to study multi-phonon transitions of the tetrahedral unit modes in BSO, BGO, BTO and mixed BSO-BGO sillenite crystals. Up to four-phonon (overtones of the F mode and combination of F and A modes) transitions were detected in BGO, BSO, and BTO and up to three- in the mixed crystals. The F mode anharmonicity, evaluated in the framework of the Morse oscillator model, was in the range 0.0024–0.0056. Fine structures due to Si-isotopes were observed in BSO. The two- and three-phonon transitions in the mixed crystals were well described by a two-mode behaviour.
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