Effect of lead fluoride incorporation on the structure and luminescence properties of tungsten sodium phosphate glasses

• PbF2​ contents as high as 60 mol% could be incorporated in tungsten phosphate glasses.
• A stong decrease of the glass network connectivity has been identified.
• The Eu3+ environment changes from oxide and hydroxyl to a fluoride vicinity.
• Radiative lifetimes and quantum efficiencies strongly enhanced with PbF2​ contents.

Tungsten phosphate glasses are known to be promising materials for several applications in optics such as non linear optical properties, lower phonon energy or photochromic effects related with tungsten oxide incorporation inside the phosphate network. In this study, lead fluoride has been incorporated in a 60NaPO3–40WO3 glass composition according to the ternary molar compositions (100 − x)[0.6NaPO3–0.4WO3]–xPbF2 with x varying from 0 to 60 mol%. The structural changes as a function of composition were investigated by thermal analysis, UV–visible absorption, Raman spectroscopy, X-ray diffraction of the crystallized samples, and Eu3+ emission in the visible. While DSC analyzes points out a strong decrease in the glass network connectivity and higher crystallization tendency with increasing PbF2 contents, Raman spectra clearly identify a progressive incorporation of PbF2 in the phosphate network with the formation of terminal PF and WF bonds. These results are also in agreement with the crystallization of β-PbF2 observed for the most lead fluoride concentrated samples. Investigation of Eu3+ emission data in the visible showed longer 5D0 excited state lifetime values and higher quantum efficiencies. These results are discussed in terms of the assumption of higher local symmetry around Eu3+ with increasing PbF2 contents.