EXAFS investigation of the Ni2+ environment in heavy-metal fluoride glasses

The nickel local structure of Ni doped heavy metal fluoride glasses of the type ZrF4-BaF2-LaF3-NaF-(BaCl2) as a function of the chlorine content has been determined by means of x-ray absorption spectroscopy. Nickel ion is surrounded by six halides in octahedral configuration in all the samples studied. At low chlorine content nickel is coordinated only by fluorine, at intermediate concentrations Ni coordinate three fluorine and three chlorine presumably in trigonal symmetry and at high Cl concentrations by only six chlorine. Our results correlates with the optical absorption spectra of Ni2+ which shows that the E-1 band characteristic of Ni2+ coordinated by six fluorine atoms changes in shape and energy position with the Cl content.