INFRARED ABSORPTION BY U CENTERS IN CSCL CSBR AND CSI

The infrared absorption by the localized vibrational modes of H- and D- centers in CsCl, CsBr, and CsI has been measured in the temperature range 20 to 300 °K. Above 100 °K, the temperature dependence of the half-widths of the local-mode absorption bands in CsBr and CsI follows a Tn dependence, where 2>n>1 (instead of n≅2, as is usually the case with the other alkali halides). Side-band structures are observed in CsCl and CsBr. These can be explained as arising from the coupling of the local-mode phonon with band phonons through anharmonic interactions. In the case of CsI, no such side-band structure is noted in the temperature range studied, except for a weak shoulder occurring very close to the main local-mode band. © 1969 The American Physical Society.