SINGLE-CRYSTAL INFRARED CHARACTERIZATION OF TERNARY SULFIDES

Infrared spectra in the 2.0-23.5 mu m region have been obtained for si ngle crystals of KInS2, CaY2S4, and SrY2S4. Diamond, ZnS, GaP, and CdS crystals served as reference samples. The observed frequencies of the first overtone (or two-phonon) bands were used to evaluate the practi cal optical cut-offs arising from the second overtone (or three-phonon ) absorption bands that occur in the long-wavelength (8-12 mu m) regio n. The resulting transparency limits of bulk ceramics of KInS2, CaY2S4 , and SrY2S4 are predicted to occur near 9.7, 11.7, and 11.4 mu m, res pectively, and are discussed in relation to the observed crystal struc tures.