Indirect electronic transitions in alkali halate crystals-II (sodium bromate and iodate) crystals

In the case of NaClO₃ and KClO₃ crystals, analysis of the long wavelength tail of their fundamental absorption revealed the active participation of the internal vibrations of the chlorate ion (Part I). In order to test the validity of the above interpretation the absorption spectra of two more halates with different anions namely sodium bromate and sodium iodate are analysed in a manner similar to that given in Part I. It is found that the principle internal vibrations of bromate and iodate ions are involved in the indirect transitions. The variation of indirect band gap with temperature is found to be ?2·5 × 10^?4 eV/K and ?2·9 × 10^?4 eV/K for sodium bromate and sodium iodate respectively.