X-ray absorption spectroscopy study of the local environment around tungsten and molybdenum ions in tungsten-phosphate and molybdenum-phosphate glasses

X-ray absorption spectroscopy (XAS) was used to study the local environment around tungsten and molybdenum ions in BaO-P₂O₅-WO ₃ and CaO-P₂O₅-MoO₃ glasses having different composition of WO₃ and MoO₃ oxides. The W L _1,3 and Mo K edges x-ray absorption spectra were measured in transmission mode at room temperature using the synchrotron radiation emitted by the ADONE and LURE DCI storage rings, respectively. The analysis of x-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) in glasses was performed in comparison with the results for a number of crystalline WO₃, CaWO₄, Na_0.66WO ₃ alpha- MoO₃, beta-MoO₃ and amorphous a-WO₃, a-MoO₃ compounds. The results of the EXAFS modeling by two different methods [(1) multi-shell best-fit procedure within harmonic approximation and (2) model-independent radial distribution function approach] allowed us to extract detailed structural information on the first coordination shell of metal (W or Mo) ions. Using the obtained data together with the information given by XRD, EPR and optical spectroscopies, we propose the model of incorporation of W and Mo ions within the glass network.