Optical spectra of thallous halides in 5d core exciton region

Reflection spectra of cubic TlCl, TlBr and orthorhombic TlI have been measured up to 30 eV by using synchrotron radiation at 16 K. In the 13-18 eV region, sharp peaks due to Tl+ 5d core exciton transitions were observed with several fine structures. The results are analyzed in terms of an atomic excitation picture. Main structures are assigned to the transitions from the ground state to the excited states with the total angular momentum J=1. Crystal-field effect on the core exciton spectra is discussed, and the fine structures are ascribed to the transitions to the J<notequal>1 states which are allowed with the aid of the crystal-field interaction.