EXAFS Investigation of the Ni²⁺ Environment in Heavy-Meta1 Fluoride Glasses

Abstract
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 ¹E band characteristic of Ni²⁺ coordinated by six fluorine atoms changes in shape and energy position with the Cl content.